Within an hour of the Sun having ushered to a close yet another scorching summer’s day, even the least imaginative among us can easily discern the outlines of a giant scorpion crawling up the sky above the southern horizon. Scorpius, the eighth and most southerly constellation of the zodiac, guards two deep sky gems near its deadly stinger. Bright enough to be seen with the unaided eye under a good, rural dark sky, these two celestial beauties are best admired with a simple pair of binoculars that you may already have lying around the house.

SCORPIUS AND ITS MYTHOLOGY

Orion, whose magnificent constellation graces our winter sky, was a mighty hunter according to Greek mythology. He was also said to be a hot hunk of manliness. Well, he said so anyways. So taken with himself, he once boasted that he could kill any living creature upon the Earth. This greatly offended the sensibilities of the Earth Mother goddess, Gaia and, in a classic “hold my beer” moment, she causes a giant scorpion to rise from out of the Earth, to attack Orion. The mighty hunter and the fearsome arachnid engage in a death duel and each opponent succeeds in killing the other. The gods were so impressed with the fight that they decided to honor the combatants by placing them both in the sky. However, so as not to disrupt the celestial harmony, one was placed in the winter sky while the other could only appear in the summer sky. By placing them in the sky at different seasons, the two were less likely to start an unseemly brawl in the heavens.

To find Scorpius, just step outside this month about an hour after sunset and face south. Look for a bright, reddish-orange star, it’s the brightest star in this part of the sky right now and you may even see it within the half hour before the Sun has even set. This star is called Antares and it represents the heart of the Scorpion. The name means “rival of Mars” because its red color sometimes makes people think that they are viewing the Red Planet. Antares is red because it is a Red Supergiant. Red Supergiants are humongous stars (in this case, some 700 times the diameter of the Sun) that have run out of hydrogen, their primary fuel source in their cores, and are currently burning and fusing progressively heavier elements before they meet their ultimate demise in a supernova explosion. As they go through their final stages, their outer layers bloat outwards and turn the star to a red-orange color.

Antares is at the center of a fishhook-shaped pattern of stars. The fishhook pattern of stars is the body of the Scorpion. To find this month’s featured objects, trace out the outline of the Scorpion’s body until you come to the tail. Use the accompanying graphic to locate the two stars that denote the tail tip and stinger of Scorpius: Shaula (pronounced “SHOWL-a”) and Lesath (pronounced “LAY-soth”). The objects we are looking for are both “open star clusters” located near Shaula and Lesath: Messier 7 (also known as Ptolemy’s Cluster) and Messier 6 (also known as the Butterfly Cluster).

LOCATING MESSIER 7 AND MESSIER 6

To find these two star clusters, grab a pair of binoculars (any pair will do but I prefer a pair of 7×50 or 10x50s, preferably the latter type, which will make the members of these star clusters really pop out) and head outside about an hour after sunset. Locate Scorpius with your unaided eye and then locate Shaula and Lesath. Use the accompanying graphic. Locate Shaula and Lesath with your binoculars and then start to scan the region to the left (east) of Shaula. It is here that you will likely find Messier 7 (M7) first, as it is the biggest and brightest of the two star clusters. Once you have M7, look towards the upper part of your FOV and you will likely find M6 in the same view. NOTE: I suggest observing from the darkest, rural sky you can find. I have found both clusters with binoculars under urban light polluted skies, but the best views will be obtained with reduced light pollution. Visit the Arkansas Natural Sky website to find a list of dark sky observing spots around the state: https://darkskyarkansas.org

Why binoculars and not a telescope? Binoculars offer a more generous FOV which brings out the grandeur of open star clusters than does the generally narrower FOV offered by most telescopes. Under a good dark sky (and with good eyesight), these clusters can both be picked out with just the unaided eye.

As I’ve said, any pair of binoculars will do but my personal preference is going to be 10×50’s or larger. I suggest purchasing an L-bracket that will allow you to mount the binoculars onto a tripod. Alternatively, you can use a reclining lawn chair and brace the binoculars on your knees.

WHAT YOU ARE SEEING

Star clusters are groups of stars that share a common origin, having formed from out of the collapse of gigantic clouds of cold, molecular hydrogen gas and dust. They are also all, to some extent, mutually bound together by gravity for some period of time. Because they all share a common origin, star clusters are particularly useful to astronomers who wish to study and model the evolution and aging process of stars over time.

Generally speaking, star clusters come in two basic forms: globular and open star clusters. Globular star clusters are giant, tightly packed, spherical masses of stars that are very old and contain hundreds of thousands of individual stars. Most globular star clusters are to be found within the halo of our galaxy and are best seen in telescopes rather than binoculars. Nearby to M7, and next to the star G Scorpii, is globular star cluster NGC 6441. To the west of Antares is another globular star cluster, Messier 4.

The other type of star cluster, and the type to which M7 and M6 belong, is what is known as an open star cluster. The members of open star clusters all share the same common origin, are all pretty much recently formed (cosmically speaking), but usually number in the dozens or a few hundred individual stars. They are much more loosely bound together than are the stars in globular clusters and will, over time, disperse themselves throughout the galaxy.

M7 has been known since ancient times. The famous Greco-Egyptian mathematician and astronomer Claudius Ptolemy lists it in his masterwork of astronomy, “The Almagest” as far back as 130 AD. He describes it as “a nebula following the sting of Scorpius”. To this day, it is also known among both professional and amateur astronomers as “Ptolemy’s Cluster”. During the 1700’s, French comet hunter Charles Messier cataloged it along with 110 other “comet impostors”, little did he know that he was compiling a catalog of the deep sky’s top choice objects to see in modern day binoculars or a small telescope. To him, they were just objects that he and his comet hunting buddies might mistake for dirty snowballs within our own solar system.

M7 contains about 80 stars that range in magnitude between 6 and 10. Astronomers use a numerical brightness, or magnitude, scale for stars and other celestial objects where the brightest objects are assigned lower numbers and dimmer objects with higher numbers. The theoretical cutoff point for naked eye visibility is around magnitude 6.

On the sky, M7 spans some 80 arc seconds, that’s 3X that of a full moon, which is why you need binoculars or a wide field telescope to appreciate its beauty. It is located nearly a thousand light years away and is estimated to be some 200 million years old. At the time these stars were being born, some of the earliest dinosaurs were evolving and beginning their ascendancy of the Earth.

M6, discovered in 1654 by Italian astronomer Giovanni Hodierna (although it was likely known long before that) is also made up of around 80 stars and spans some 20 light years across. It is located a bit further out than M7 at an estimated 2,000 light years and is also considerably younger at around 50 to 100 million years of age. Being so young it is more compact than M7 and when you look at it through a pair of 10×50 binoculars or a small telescope (say, around 4” of aperture) you can see that the stars are arranged in an X-pattern, lending some people to think that it resembles a butterfly with its wings outspread. Many of the stars comprising M6 are very large, very hot spectral type O and A stars. These massive kinds of stars live fast and die young and a few of the cluster’s largest stars have already begun to show signs of aging by having evolved into yellow, orange, and red giants.

Since you have your binoculars and are already outside looking about, take some time to use the binoculars to scan the length of the summer Milky Way, which sweeps through the tail of the Scorpion and then arches high overhead, through Cygnus the Swan and on to the NE. Even if you cannot readily see the Milky Way with your unaided eye, you will still be rewarded with much starry splendor as you peer inwards to our Galaxy with this edge-on view. It’s a stunning sight and it’s bound to fill you with much awe and wonder.

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WHAT IS A LUNAR ECLIPSE

A lunar eclipse is what happens when the Earth can cast its shadow onto the moon’s surface.  For the Earth to do this it must be in between the moon and the Sun and the only time this kind of alignment can occur is during a full moon.  Likewise, the only time we can see a total solar eclipse is when the moon is in between the Earth and the Sun, and this kind of alignment can only occur during a new moon phase.  Okay, you might be asking: if we have both a new and full moon roughly once a month, why do we not see an eclipse of some sort every month?  The answer is the alignment between all three objects must be very precise and that level of precision obviously does not happen every month.  Why pray tell is that?  Well, it’s all because the moon’s orbit around the Earth is set on an incline of about 5 degrees with respect to our planet’s orbital plane around the Sun.  The upshot of all of that is that, during a new moon, the moon is either below or above our line of sight to the Sun and, so it does not block our view to create a total solar eclipse. During a full moon, the moon is usually positioned somewhere outside of the Earth’s shadow and, so, we do not see a total lunar eclipse every full moon.  An orbital incline of 5 degrees might not sound like a lot but it is just enough to keep all three of the major celestial players in these eclipse games from being in perfect alignment to create an eclipse on any regular basis.  And that might not be such a bad thing because if it were, I’m sure we humans would soon become blasĂŠ about monthly eclipses as well.

THROWING SHADE

Before we go into the details for the timing of this month’s eclipse, it would be best if we understood a bit about the Earth’s shadow and just how the spectacular effects of a lunar eclipse are created.

Lunar eclipses occur whenever the moon passes through the Earth’s shadow and, just like your own shadow, the Earth’s has two parts: the “penumbra” and the “umbra”. The darkest part of any shadow is the umbra (think, “umbrella”) while the outer, dimmer region of a shadow, is called the penumbra (think, “almost but not quite full shade”). Because the Earth is a sphere and because the light source, the Sun, is in the apparent form of a large, bright disc in the sky, the shape of Earth’s shadow is a cone. The long, tapering cone-shaped umbra of Earth’s shadow extends for about a million miles out into space.  The moon is, on average, about 239,000 miles away, so we have a lot of shade to potentially cast onto the moon provided that alignment conditions are just right. Depending on just how far the moon penetrates into the Earth’s shadow, you can end up with three different kinds of lunar eclipse.  If the moon just skirts the outer, dimmer shadow, you get a “penumbral eclipse”.  Not much happens in a penumbral eclipse and, to be honest, you can’t really tell that anything of significance is occurring.  But once the moon slides into the umbra, things become much more noticeable. Once inside the umbra, it looks as though a dark stain is slowly creeping across the lunar surface. If the dark stain created by the umbra encompasses the entire illuminated side of the moon facing the Earth, you then have a total lunar eclipse.

Perhaps you have either seen or heard about “blood moons”, where the lunar surface becomes either a copper or deep red color.  What’s up with that? Well to answer that, let’s say that you were on the moon, looking towards the Earth, during a total lunar eclipse.  Consider this, as you stand upon the lunar surface you would see the Earth go through a series of phases over time, just like we see the moon go through phases from our vantage point back here at home.  Except, you would see the exact opposite Earth phase from the moon phase that we are seeing here on our home world.  For example, during a total lunar eclipse, here on Earth, we see the moon at full phase because the alignment in the sky is like this: moon->Earth->Sun. But from your POV on the moon, you would see Earth along your line of sight to the Sun and, to you, the Earth would be at new phase.  As the bulk of the Earth covers up the Sun, you would then see a bright red-orange ring of light encircling the Earth. This is all the sunrises and sunsets that are happening on Earth at this moment in time.  It is the Sun’s light passing through and then becoming refracted as it passes through the Earth’s atmosphere.   This refracting and filtering of sunlight through the Earth’s atmosphere scatters out the short wavelength blue portions of the light, allowing the longer wavelength redder portions to pass on through, creating the reddish tinged light that is now illuminating the lunar surface.  It’s the same process that creates the red sunrises and sunsets here on Earth and because the Earth’s atmosphere is a very fluid and dynamic medium, the exact tint of red can vary greatly from one lunar eclipse to another.   On very rare occasions, if there are a lot of volcanic particulates in the upper layers of the Earth’s atmosphere, the moon may turn black in color, or disappear altogether.

WHEN AND WHERE TO LOOK

On the evening of Sunday, May 15th, the full moon will rise in the SE.  Here is a breakdown on the timing of events that I’ve lifted from the Time and Date website, a great resource for the timing of celestial events such as eclipses and meteor showers.

A few other things to think about as you view the eclipse…

Each month’s full moon has a name associated with it, often derived from Native American culture.  The names are intended to reflect some aspect of nature that is taking place within each month.  For the month of May, the full moon’s name is “the full flower moon” because it is the time of year when many plants are opening their blossoms.

Earlier, I mentioned that the moon is, on average, about 239,000 miles away from the Earth.  The reason that there is an average is that the shape of the moon’s orbit around the Earth is not a perfect circle with the Earth in the exact center.  Instead, it’s orbit is in the shape of a somewhat squashed circle, an ellipse.  As a consequence, the moon’s distance from the Earth always varies.  When it the moon is at its most distant point in its orbit, we say that it has reached “apogee” and when it is closest to us (and thus appears a bit bigger) it is at “perigee”.  This full moon will occur right around perigee, so the moon will be about as large as it ever gets.

The moon will be at its darkest, and most red, during totality.

You do not need any special equipment to view the eclipse, but you will find that binoculars or a small telescope (which you can obtain from many local public libraries in the central and NW AR areas thanks to funding from the Arkansas Space Grant Consortium) will enhance the view.  I am not a skilled photographer and imaging the moon can always be a tricky proposition, even for the skilled photographer.  The easiest way that I have found to image a lunar eclipse is by using the method of afocal photography.  This simply involves holding the eyepiece of my cell phone camera up to that of a telescope aimed at the moon.  Try it if you have access to a scope.

While the eclipse can be viewed under just about any level of local light pollution, be aware that the Central Arkansas Astronomical Society will be offering a viewing party from their River Ridge Observatory near Wye Mountain.  For details, visit their website at www.caasastro.org. Also, should the event be clouded out locally, be aware that websites such as NASA and Time and Date will provide livestreaming of the eclipse as well.  The main thing I want to get across is that you just get outside, have fun, and to look up in both awe and wonder.

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As the planets of our solar system move around the Sun in their various orbits, and at their own individual speeds, from our vantage point here on Earth (which is also moving around the Sun) we see them appear to wander against the starry background. On not so rare occasions, we will see two or more of them meet up with one another for what appears to be a close grouping. These close pairings or groupings are called “conjunctions” and they can make for interesting naked eye observing. As I said, conjunctions are generally not so rare, there are often one or more each month. But some alignments are rarer than others. For example, close pairings between Jupiter and Saturn, such as the one we saw in December of 2020, only happen once every 20 years or so.

In contrast to conjunctions are parades of the 5 naked eye planets upon a small region of the morning or evening sky. These events are a bit rarer and generally happen every few years. To the best of my knowledge, there is no official designation for such alignments and I just refer to them as “planet parades”. This month we will get to see 4 of the five naked eye planets form a parade across the predawn sky and, when we throw in a waning crescent moon you’ve got yourself a lovely cosmic spectacle.

WHEN AND WHERE TO LOOK

Before we get to the prime dates around mid-month, I urge you to get outside an hour or two before sunrise on April 4th. Face southeast and you will see Mars and Saturn in a very tight conjunction. Make sure that your view is unobstructed towards the horizon. The planets will appear as two bright points with Mars being the one that is redder in terms of color. Bright Venus is off to the left. I want you to pay close attention to where the planets are located and their apparent closeness to one another. This will change as the Earth, and the other planets continue to go about their orbits around the Sun. Notice how different this arrangement will be in the weeks ahead.
You may have noticed that we are missing our 4th bright planet in that April 4th conjunction. Who’s missing? Why it’s Jupiter, King of the Planets. By around the 17th, Jupiter can be seen inching its way up above the eastern horizon and it’s on the 23rd that the planet parade really gets going. On the morning of the 23rd, about an hour or two before sunrise, go outside and face east. Provided that your view to the horizon is unobstructed and the sky is cloud free, you should see Jupiter and Venus shining brightly just above the horizon. Let your eye trace out an arc heading towards the west, and you will see Mars and Saturn as well. Just to the west of Saturn, you will find the waning crescent moon. Wow, what a beautiful sight! As an added bonus, but a challenge object to see, will be the planet Neptune, just to the right of Jupiter. You will need binoculars or a telescope to see it. Conspicuous in its absence is fleet footed Mercury, whose presence is only to be found in the evening sky later this month.

After the 23rd, watch closely as, each morning, the moon appears to pair up with different planets as it heads lower and lower in the sky over the following mornings. It appears to move more quickly compared to the more distant planets because it is closer to Earth and orbiting at a faster rate (it completes one orbit around the Earth once every 27.3 days). The path across the sky in which the planets, moon, and Sun all appear to traverse is known as the “ecliptic”. It’s largely an imaginary line but it does represent the orbital plane of the Earth around the Sun, and the moon and other planets also all orbit in roughly this same plane as well.
But what if you miss this particular alignment? Don’t fret, the moon will continue to glide amongst the planets up until month’s end while the planets themselves will remain around in their alignment for several weeks in May, albeit with a bit of a switcheroo. On the morning of May 1st, Venus and Jupiter will be so close together upon the sky, you may need binoculars to separate them. Over the coming days thereafter, it will appear as though Jupiter has overtaken Venus and left it behind as it continues to rise higher and higher in the early morning sky. Later in the month, on May 21st, the moon again appears among the morning planet parade. But the parade becomes even more spectacular in June. On the 24th of that month you will see the five naked eye planets spread out across the sky: Mercury, Venus, Mars, Jupiter, and Saturn. Adding even more grandeur to all this eye candy will be the crescent moon on this date. Holy planetpalooza, Batman! The downside is that they are all spread out across such a large area of sky that you will not be able to get them all in a single photo like you can with the four planets and moon this month.

WHAT YOU ARE SEEING

As you gaze upon spectacles like this you are doing so in two dimensions and it’s easy to forget that the reality before you is actually taking place in three dimensional space. What you are seeing is not like the image depicted in the graphic below.

Ever since grade school, we’ve all seen graphics like this that show the planets all lined up in a row. This is poetic license on the part of the artist and is done merely for the sake of convenience. The odds of you living long enough to see anything even remotely like this illustration are, well, astronomically low. Yes, all the planets orbit more or less within the same plane around the Sun. But there is a very important factor that undermines the idea you might come away with after looking at an image like this. Namely, because of the way the orbits are oriented and tilted the eight major planets of our solar system can never come together in such a perfect alignment. During one close approximation of such a configuration, during the 1970’s when the outer planets were in a once-every-175-year alignment, NASA decided to take advantage of it when sending the twin Voyager probes out to explore Jupiter, Saturn, Uranus, and Neptune. This so-called “Grand Tour” allowed the spacecraft to use the gravity of each planet as an assist to send them on to their next destination. Kind of like a gravitational stepping stone assist in order to hop to the next planet without the need to use fuel to propel them on.

In the case we now have before us, keep in mind that the planets are not aligned like they are in the graphic, they are all staggered out at different distances and in different positions relative to one another and to the Earth. Bottom line: you are just seeing a line of sight perspective that gives the illusion that the planets are all arranged in some kind of unique, straight line configuration. The main thing I want to impart to you is to just get outside and enjoy this snapshot in time as the planets and moon go through their minuet around the Sun. I’m sure that just the pure aesthetics of such a sight are enough to leave you in both awe and wonder.

The post April 2022 Feature – A PARADE OF PLANETS appeared first on University Television - Comcast 61/1095 & UVerse 99.

Today, all we need to do in order to know when winter officially ends and spring begins is to consult a calendar or the internet.  But what did folks in ancient times use before the invention of things like calendars, smart devices, or the internet?  Sure, your average Joe or Jane prior to 1500 BC (about the time the first sundials were invented in Egypt) probably didn’t need precision time keeping devices in order to regiment their lives, but when it came to inventing agriculture and building the civilizations that would ultimately thrive from such endeavors, it did become practical, if not vital, for them to be able measure time beyond the day and night cycle.

At some point, our distant ancestors realized that it was possible to measure the progression of time by visualizing it as having a cyclical, as well as a linear quantity.  In other words, from the perspective of birth to the grave, time seems linear, but, if you are an observer of Nature, there is also a definite circular aspect to time as well.  The motion of the stars across the night sky, the series of lunar phases, the rising and setting of the Sun, and the progression of the four seasons are all obvious examples of Nature’s repeated cycles.  By carefully and constantly observing what was happening in their world, our ancestors were able to devise various types of calendars that would allow them to reckon both past and future time.   In doing so, they could establish dates to record their history, commemorate important events, celebrate religious festivals, to know when rains or droughts may come, and to know when to plant and harvest crops.  The arrival of Spring, especially after the long deprivations of winter, must surely have been an important time for our ancestors across much of the Northern Hemisphere.

If you ask most people why we even have seasons, you will usually get some kind of vague answer about it being related to the Earth-Sun distance. If it’s the dog days of sultry summer, they might say that the heat is a result of the Earth being at its closest point in its orbit to the Sun. If it’s the bleak midwinter, then the freezing temperatures are often thought to be the result of the Earth being far away from the Sun. This is all incorrect.  While it is true that the Earth’s orbit around the Sun is shaped like an ellipse, resulting in an ever-varying distance from the Sun, it has nothing to do with the seasons.  For example, in January, the Earth is actually at its closest point to the Sun, while in July, it is at its most distant.  The real reason for the seasons has to do with the fact that the Earth is tilted upon its axis by 23.5 degrees.   But before I get into how that brings about the seasons, let’s find out why the Earth is tilted in the first place.

To answer that question, we must journey back in time to around 5 billion years ago to a time when there was no Earth, no Sun, no solar system.  Somewhere out in space, there was a huge, amorphous cloud of cold hydrogen gas and dust.  In some areas of this vast cloud, the gas and dust tended to bunch up into dense knots. These knots would attain more mass than surrounding sections of the cloud and before long, gravity began to work its magic.  For one particular knot, gravity began to pull more and more material together, making it even more dense.  As material fell towards the center of the knot, the temperature and pressure at the core became so extreme that the natural tendency for hydrogen atoms to repel one another was overcome and they began to fuse together, creating the heavier element helium and also liberating a great deal of energy in the form of heat and light.  At this point, our Sun was born.

Surrounding the infant Sun was a giant disc of leftover gas and dust.  From out of this material would condense the planets, dwarf planets, moons, asteroids, and comets that make up our solar system family.   But the Sun’s powerful gravitational influence created instability in the disc and this turmoil allowed for the shifting orbits of planets and the collisions of young planetismals and protoplanets (objects that were theoretically on their way to becoming full fledged planets).  This was a violent time in our solar system’s history and around 4.5 billion years ago, a Mars-sized object that astronomers have named Theia, collided with the infant Earth. This collision resulted in Theia and the Earth melding together, with the exception of some material that got flung out into space and which would eventually come together to form our moon.  As a result of this collision, the Earth got knocked off its perpendicular rotational axis by about 23.5 degrees.  The stabilizing effect of the moon’s gravity has held it mostly that way ever since.

In a roughly 24-hour span of time, the Earth spins once upon its tilted axis.  It spins from west to east but the visual illusion this creates is that the Sun, stars, moon, and planets appear to rise in the east and set in the west.  As the Sun traces its daily path across the sky we see it increase its altitude from sunrise before reaching its highest point at local noon, and then decreasing in altitude as it heads into afternoon and evening.  But there is also an apparent seasonal change in the Sun’s altitude over the course of the year as well, with the Sun appearing higher up in the sky during summer and then becoming lower in the sky during winter.  This change in altitude is all due to the Earth’s tilted axis and its ever-changing orientation to the Sun as we make our annual trek around it.  The seasonal change in altitude also means that, for most of the year, the Sun does not rise due east or set due west. More on that in just a minute.  It is this varying altitude of the Sun and its rise and set points along the horizon in relation to the cardinal points on the compass, that people in the ancient world paid so much attention to in order to create calendars and forecast the seasons.

To visualize all this, consult the graphic I’ve included that shows the Earth at four different points in its orbit around the Sun over the course of a year.  Over the course of one complete lap around the Sun, you will note in the graphic, that the angle of axial tilt does not change, it’s always at 23.5 degrees.  The north and south axis, extended outwards from the poles, always point in the same direction in space (NOTE: over spans of geologic time, the tilt does vary but that’s another story altogether).  At this point in time in our planet’s history, the north axis points pretty close to the star Polaris, the “North Star” (this does, has, and will change over time).  What does change over the course of a year is the orientations of the globe’s hemisphere’s with respect to the Sun.   Take a look at the Earth depicted in the graphic for the month of June.  Note how the Northern Hemisphere is pointing towards the Sun while the Southern Hemisphere is pointing away from it.  It is at this time that the Sun is highest in our sky here in the Northern Hemisphere and lowest in the Southern.  Here in the north, we receive more of the energy that the Sun is radiating out into space from all of that nuclear fusion taking place within its core, and we experience summer.  Down south, they are tilted away from the Sun, receiving less solar energy and, so, they experience their winter.

Look back at the graphic again to the dates in March and September.  Notice how on these two dates that neither hemisphere is either angled towards or away from the Sun and its rays are now shining down upon the equator, giving both hemispheres roughly equal amounts of both day and night.  Here in the Northern Hemisphere, our temperatures tend to become milder compared to the extremes of winter and summer.

Now, let’s go back and pull some of this information together.  If you were to ask most folks in which direction the Sun rises and sets, they will tell you that it’s east and west (dummy!).  But they would be wrong. Sorta.  Yes, the Sun rises in an easterly direction and sets westwards, but there are actually only two days out of the year where the Sun actually rises due east and sets due west.  For other times of the year, the Sun rises and sets south of east/west or north of east/west.  Once again, let’s go back to the graphic that shows the Earth at four different points in its orbit around the Sun.  On December 21st, if you were outside observing (and you really should if you’ve never done this before) you will notice the Sun rising the furthest south of east and then, later, setting furthest south of west.  This is the shortest day of the year and it marks the beginning of winter.   December 21st is called the winter solstice (“solstice” is a combination of two Latin words: “sol” = “Sun” and “sistere”, meaning, “stand still”).  The Sun remains low in the sky throughout the winter months but it appears to alter its migration southwards on December 21st and slowly begins to head northwards.   Six months later, the Sun reaches its most northern point along the eastern horizon at sunrise and then again when it sets north of west later that day.  This is the longest day of the year and we call it the summer solstice, the first day of summer.  On this day, it appears to stop in its north bound track, turn around, and slowly head southwards until it once again does an about face on December 21st.  Throughout the summer months, the Sun rises north of east and then sets north of west.

Now, look at the Earth for March and September.  Remember, neither of Earth’s hemispheres is now angled towards or away from the Sun, its rays fall directly onto the Earth’s equator and we have roughly equal lengths of both day and night. We call these two days of the year equinoxes (from the Latin meaning “equal night”).  The one in March occurs roughly on March 21st, although this year it falls on March 20th.  The March equinox is also called the “vernal equinox” (from a Latin word referring to “spring”).  The other equinox occurs around September 23rd and it marks the first day of fall.  It is sometimes called the “autumnal equinox”.  On, or around March 21st, the Sun crosses over the celestial equator (an imaginary line in the sky which is simply the projection of Earth’s equator out into space) as it goes through its apparent migration from its wintertime sojourn in the southern sky towards its northern occupation of the summer sky (for those of us here in the northern hemisphere).  It again crosses over the celestial equator in September but headed in the opposite direction.  The thing to know here is that as the Sun appears to cross over the celestial equator on these two days of the year, it will appear to rise and set due east and west.  Once again, I encourage you to get outside and check this all out for yourself and then track the Sun’s altitude and rise and set points over the course of the year.   It’s a rewarding experience, especially if you combine it with regular observations of things such as lunar phases and the nightly motions of the stars across the sky (learn a few star names and constellations each month as well).  By doing so, you will gain not only a practical sense of the motion of the sky but how to navigate it as well (a useful thing if you ever decide to own a telescope).  Another benefit from such sky watching activities is that, with practice and repetition, you will begin to gain a certain mindfulness, or awareness of both you and the universe around you.  In other words, you can regain a connection with Nature on the grandest of scales, something our ancestors were far more in tune with than we are today.

Consider this when you are observing the sky over the course of the four seasons (or if you are just out and enjoying a nice walk on a temperate spring day): while every planet in our solar system experiences some kind of seasonal change, there are several for which that change is negligible.  I mentioned earlier that the Earth’s varying distance from the Sun does not play a role in determining our seasons and that’s true enough but it’s not necessarily true for the other planets in our solar system.   The size of a planet’s orbit, the size of the planet itself, its atmosphere (if it has one), and its degree of axial tilt are all contributing factors to a planet’s seasons.  Take for instance Venus.  Venus, with its runaway greenhouse effect, 900-degree Fahrenheit surface temperature, and sulfuric acid laced clouds is not a very pleasant place to visit.  Venus tilts upon its axis by only about 3 degrees and while it has seasons, there is little to distinguish them apart from one another.  Neptune, the 8th and outermost planet in the solar system, tilts upon its axis by 28.5 degrees, not too different from our own.  The gas giant planet does have distinct seasons but there are some notable factors that influence them.  For one, Neptune is placed so far away from the Sun that any energy it receives from is going to be rather paltry.  However, Neptune’s core generates a lot of heat and it is this that drives most of the planet’s weather.  Since it takes Neptune almost 165 of our years to complete just one trip around the Sun, each season lasts for about 41 Earth years.  Life on Earth has evolved on a world with a 23.5-degree tilt, which is held fairly constant by the gravitational interaction with its only natural satellite (itself the product of a chance collision with the infant Earth 4.5 billion years ago), at a Goldilocks distance from its parent star where temperatures are just right to contain liquid water and moderate temperatures.  Who can say how, or if, life might have evolved if conditions were otherwise.  Food for thought as you gaze up into the skies of blue-green planet Earth in both awe and wonder.

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Cupid is up to his usual shenanigans on the 14th but I’m going to share with you some of my love for observing the moon and the planets with several dates in February. Don’t fret about needing a telescope to enjoy most of these sights, but a pair of regular old binoculars that you have lying about the house may be a useful supplement to your bare-naked eyeballs.

DATES TO REMEMBER

FEB 2 – A young crescent moon meets Jupiter in the early evening

Feb 7 – The crescent moon hangs out with the ice giant, Uranus

Feb 9 – Venus is at its brightest

Feb 25 & 26 – Bright Venus is near the waning crescent moon. BONUS: the moon also appears near the deep sky star forming factory, Messier 8 on the morning of the 25th.

Feb 27 – The thin waning crescent moon forms a lovely conjunction with Venus and Mars

WHAT YOU ARE SEEING

Jupiter, the largest planet in the solar system, has been a familiar presence in our evening sky since August of 2021 but by the month’s end it leaves the scene, becomes a morning object, and reappears to the evening sky in September of this year. On February 2nd, step outside around 30 minutes after sunset and face westwards to see it very low in the sky. With a pair of binoculars or a small telescope, see how many of the planet’s four largest moons (Jupiter has a total of 79 known moons) are visible: Io, Europa, Ganymede, and Callisto (I’ve listed them in their order of distance from the planet, innermost to outermost). Sky & Telescope offers an app called, appropriately enough, “Jupiters Moons” that will show you where they are within their orbit around the planet at any given time, but there are some generalized stargazing apps that have that feature as well.

If you do use binoculars this evening, be sure and scan the sky to Jupiter’s lower left at this time as you may see a 2-day old moon, around 5% illuminated. This can be a challenge to pull out of the murk when looking so low in the sky. If you are a member of an astronomy club, chances are that they are affiliated with the Astronomical League, an umbrella organization for amateur astronomy clubs that helps promote the hobby and hone observing skills by having participants complete various observing programs. One of these programs involves lunar observing with binoculars and seeing the 2-day old waxing crescent moon is on the checklist of observing challenges. If you are affiliated with the League, then upon successful completion of any of their observing programs, you get a certificate, a lovely pin, and the satisfaction of knowing that you have sharpened your observing skills as an astronomer. You can still complete any of their programs, but you cannot submit your observing logs and collect either pin or certificate unless you are affiliated with the League via membership within a participating astronomy club. Visit the League’s website here: https://www.astroleague.org Alternatively, check with your local astronomy club to see if they are affiliated with the League.

On the evening of the 7th, go outside and find the crescent moon while facing the SW. With a pair of binoculars or a small telescope, look just to the moon’s lower right to see a blue-green point. This is the planet Uranus. Uranus is the third largest planet in the solar system, with a diameter four times that of Earth’s. But it’s also some 1.8 billion miles away and, so, most people have not seen it. This pairing of the moon and Uranus will help you locate the ice giant world. Being so far away from the Sun, Uranus and Neptune are very much colder than the other planets and their atmospheres are laden with water ice and other icy compounds such as frozen ammonia. Therefore, we call them “ice giants”. Why are they so blue? Well, the ammonia in their atmospheres is very good at absorbing the redder portions of the Sun’s light while reflecting back the bluer portions and, so, Uranus and Neptune appear blue-green to our eyes.

Venus, named for the Roman goddess of love and beauty, second planet from the Sun and our closest planetary neighbor (coming as close as 27 million miles to Earth but is, on average, about 31 million miles away) dropped out of our evening sky early last month and has now become our “Morning Star”. It will remain a morning planet until December of this year, when it will once again shine bright in the evening sky. On February 12th, Venus reaches its greatest illuminated extent, meaning that, seen through a telescope, the apparent size of its disc is at its largest. But here’s the kicker, Venus will only appear as a crescent. Whaaa? First off, yes, Venus goes through phases, just like the moon does. Mercury, the innermost planet, does to. Why? Well, as these two planets orbit inside Earth’s orbit, we see that their orbital positions, relative to the Sun and Earth, are constantly changing and, so, we see different areas of their surface becoming illuminated and then passing into shadow as they complete their laps around the Sun. If you have access to a small telescope (the NASA Arkansas Space Grant Consortium, based at ĚÇĐÄVlog´ŤĂ˝ Little Rock, has funded a number of libraries across the state, including the Central Arkansas Library System, with telescopes that patrons can check out just like a book), then be sure and train it on Venus in order to see its phase.

But, if it’s just a crescent, why is it so darn bright? There are a couple of reasons for this. You would think that it would be brightest at full phase, right? But that full phase (or, near full) only occurs when Venus is on the far side of the Sun, placing it very far away from Earth. At such a great distance, it doesn’t appear very bright. But, during a crescent phase, it is getting much closer to Earth and that makes the brightness factor really crank up. The other thing to remember about Venus’s brightness is the fact that the planet is entirely blanketed in clouds that are laced with liquid droplets and tiny crystals of sulfuric acid. The sulfuric acid droplets and crystals are very efficient when it comes to reflecting sunlight and that’s what makes Venus so dang bright. On the morning of the 9th, step outside and face east to see Venus shining at a magnitude of -4.6, it will not be this bright again in our sky until July of 2023. As a side note, when Venus is this bright, it is often reported as a UFO sighting.

About an hour before sunrise on the mornings of February 25th and 26th, look towards the SE to see Venus, low in the sky, with a beautiful waning crescent moon off to the lower right. Once again, a pair of binoculars may prove useful for this particular observing opportunity. On the morning of the 25th, look to the left of the moon, using binoculars or a small telescope (and as dark a sky as you can find) and you just might see place where stars are being born. Known as Messier 8, or the Lagoon Nebula, this stellar nursery is located over 5,000 light-years away in the constellation of Sagittarius. In binoculars, you can see the nebula as a faintly glowing, fuzzy cloud; with a small telescope, you can begin to appreciate more of its intricate structure. The glow is created by the newborn stars energizing the gas in the cloud. The ultraviolet radiation the young stars emit gives an energy kick to the atoms of hydrogen that makes up the gas cloud. As the atoms return to their normal energy state, they emit a faint glow and that is what you are seeing in your binoculars or telescope. Our morning sky is a sneak preview of what we are going to see in our evening sky a few months hence. In summer, Sagittarius and Messier 8 are prominent in the evening sky and, on moonless nights, you can just barely see the nebula as a faint, glowing patch upon the sky (provided you are observing from a dark sky locale).

Finally, on the morning of February 27th, check out a beautiful waning crescent moon just to the lower right of bright Venus. Mars, the fourth rock from the Sun, is fainter but can be found in between the two. Many of the newer smartphone models are equipped with cameras sensitive to image many of the things we’ve talked about here, including this one. If you own one, try it out, it can only help enhance your awe and wonder with the universe in which you live.

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As we enter the upcoming holiday season, many folks will have likely requested stargazing kit of one sort or another as part of their gift receiving wish list.  I know this to be true because binocular and telescope sales continue to be at an all-time high while memberships in amateur astronomy clubs all around the world are on the rise.  Such tidings do my heart good and I am “over the moon” (sorry, couldn’t let that one go by) in knowing that more and more people have taken up the art/hobby/science of stargazing.  Whether you are wanting to learn astrophotography or just the names of a few of the stars and constellations, amateur astronomy has a little something to offer a wide range of tastes and interests.  The main thing is that you become active and just spend a little time outside at night looking up every now and again.  Seeing as how many of us will be on break over the holidays, now is the perfect opportunity to set aside some time to do just that.  For this month’s blog, I offer you three opportunities to get outside and take in the celestial sights.

COMET C/2021 A1 (LEONARD)

Everyone likes to see a nice, bright comet and Comet Leonard may well be as good as it gets for the year.  First spotted back at the beginning of the year by astronomer Greg Leonard at the Mount Lemmon Observatory in Arizona, Comet Leonard has shown promise right from the start.  Upon its discovery, there were clear indications of a tail forming, even though it was still located out near the vicinity of Jupiter (most comets don’t begin to spout a tail until they are somewhere near the orbit of Mars).  It has only continued to brighten as it makes its way through the inner solar system.   Right now, the comet is not visible to the unaided eye but can be seen during the morning hours with either binoculars or a small telescope under dark sky conditions.  During the early days of December, look for it in the predawn skies near the bright star Arcturus.   By mid-month, Comet Leonard will have transitioned to an early evening object and can be seen near Venus between December 14-16, just after sunset in the SW.  The caveat here is that it will be very low in the sky and could be difficult to pick out unless you have a clear, unobstructed view down to the horizon.  The good news is that its proximity to Venus will be a helpful guide in locating it.   Comet Leonard is a long period comet, and its orbit takes it from the outer regions of the solar system in a shell-like reservoir of icy bodies known as the Oort Cloud, into the inner solar system every 80,000 years or so.  But, before you start making plans to see it on its next pass, be aware that Leonard is now on a hyperbolic orbit, meaning that it now exceeds the escape velocity of the solar system and, once it has its close encounter with the Sun in January, it’s vaya con dios, as it exits the solar system and ventures out into interstellar space, never to return.  As to how well Comet Leonard will perform, just remember, comets are notoriously unpredictable in how they behave.  So, take any predictions about how bright the comet will become with a hefty dose of salt.  Go to websites such as EarthSky or Sky & Telescope to get the latest news and charts that will help you locate it easier.

GEMINID METEOR SHOWER

Quick: what’s the best meteor shower of the year?  If you answered, “the Perseids”, then I’m sorry, that is incorrect.  If you want to observe the most productive meteor shower of the year, then you need to check out December’s Geminids, not August’s Perseids.  The Perseids are always listed as everyone’s favorite but that probably has more to do with the fact that the weather is nice and warm for observing, while the Geminids requires that you bundle up and drink lots of hot beverages.  The Geminids are often touted as producing up to 120 to 150 meteors per hour.  While this is, on average true, it assumes that you are observing under optimal conditions, something that is very rare.  On top of that, on the peak night of December 13th and into the predawn hours of December 14th, the moon will be 78% full and up practically the entire night.  Bummer.  But, it’s not exactly a lost cause.  If you seriously dial back your expectations and plan accordingly, you can still see meteors.  How many?  I have no idea.  But if you don’t get out and look, you won’t see any at all.

Here’s what you need to know.  The Geminids are active from November 19th to around December 24th (remember, the peak is the night of the 13th and into the morning hours of the 14th), so you can see some Geminids just about any night over this time period.  The parent body of the Geminids is not a comet, as is the case with most meteor showers.  Instead, the parent body is an asteroid named 3200 Phaethon.  The rocky rubble left in its wake creates some very bright and distinctly colored meteor streaks in our December night skies, so it is possible for a few of them to overpower some of the glare from the moon (still, the show would admittedly be better without the moon).   On top of that, you can start looking for Geminids before midnight as the radiant, which is in the constellation of Gemini, is well above the horizon during the evening (the radiant is just the apparent direction on the sky from which most of the meteors seem to radiate from).  Still, the best times for observing will be after midnight, say around 1:00 AM or 2:00 AM.  On the peak nights, I would suggest looking during the predawn hours when the moon is either low in the sky or below the horizon.  The key things to remember here are: get away from the city, bundle up, stay warm with hot beverages, get comfortable in a sleeping bag or lawn chair, and look up.  Also, bring along some good friends and good tunes.  Holiday memories are made when you share these kinds of things, even if you don’t see many meteors.  If you want to find a good observing site, please visit the Arkansas Natural Sky website for a list of possibilities:

MERCURY AND VENUS CONJUNCTION

Last year, we had an impressive pairing of Jupiter and Saturn on December 21st.  These kinds of line-of-sight effects are called “conjunctions” and we have another nice pairing this year with Mercury and Venus, albeit not quite as impressive as last year’s meetup with the two largest planets in our solar system.   On December 28th, if the sky is clear, get out just after sunset and face the southwestern sky to see Mercury and Venus in the same binocular field of view (Mercury, the innermost planet, can be seen with the unaided eye but stands out nicely from the twilight with a little help from an inexpensive pair of binoculars).   Jupiter and Saturn can be seen just above and to the left of the pair, with Jupiter shining more brightly than the more distant Saturn.  Watch closely over the next 10 days as Mercury climbs higher in the sky while Venus drops lower.  Venus is at its brightest this month on December 3rd but it will disappear from our evening sky on January 9, 2022.  At that time, Venus will be passing in between the Earth and the Sun, something that astronomers call “inferior conjunction”.  It will disappear for a while from the evening sky but will later reappear as a morning object.

These are just a few of the things you can see in our December sky for 2021.  I hope that the year has been kind to you and I wish you all the best during this holiday season and for the upcoming new year.  May you all have clear skies for 2022!

The post December 2021 Feature – HARK, YE MERRY STARGAZERS! appeared first on University Television - Comcast 61/1095 & UVerse 99.

The people of ancient times viewed the night sky with a mixture of awe, wonderment, reverence, and, on occasion, with a certain amount of fear.  The latter emotion often arose whenever something unpredictable or out of the ordinary appeared in the sky.  The sudden appearance of a bright comet, the Sun slowly disappearing as if a giant, invisible snake was swallowing it, or the moon becoming a blood red color were all regarded as bad omens.  And who could blame them for looking up in fear?  Without knowing why these things were happening, any one of us would surely feel a sense of dread or terror upon witnessing such an event.  We’ve learned a lot over the intervening centuries about these kinds of phenomena and, for most of us, fear is no longer a part of the equation anymore.  Nevertheless, at the mention of the word “eclipse”, be it a solar or lunar eclipse, people tend to get excited about the prospect of seeing one firsthand.  Thanks to the celestial mechanics of our solar system, on Friday, November 19, 2021, we will be treated to the magic of a partial lunar eclipse.

WHAT ARE ECLIPSES?

In simple terms, an eclipse is what happens when the light from one celestial object is temporarily dimmed or blocked due to it crossing into the shadow of another celestial object, or because the other object passes in between the first object and the line of sight of an observer.   For example, a solar eclipse is what happens when the moon blocks our view of the Sun and a lunar eclipse is what happens when the Earth gets in between the moon and the Sun, with the Earth casting a shadow onto the lunar surface.

But let’s put aside solar eclipses and focus on the lunar variety. Remember, a lunar eclipse is what happens whenever the Earth is throwing shade onto the moon.  In order for that to happen, we must have an alignment like this: moon->Earth->Sun.  The only time we have an alignment like this is at full moon and that’s why lunar eclipses can only be seen during this phase (likewise, a solar eclipse can only occur when the moon is in between the Earth and the Sun, and that only happens during new moon).

If you are paying attention, you might be wondering why, if we have a full (and new) moon each month, do we not see eclipses all the time.  The answer is that the alignments between the moon, Earth, and the Sun has to be, as Goldilocks so succinctly put it, juuuuust right.  There are two things that prevent these just right alignments from happening more often.  First off, the moon’s orbit around the Earth does not align with the Earth’s orbital plane around the Sun; the moon’s orbital plane, relative to our own, is inclined by about 5 degrees. The only way we can see an eclipse is when the moon happens to be crossing through our orbital plane during the time of a full or new moon.   The second complication is that the moon does not orbit theEarth in a perfect circle, it does so in a kind of egg-shaped pattern called an “ellipse”.   If it orbited in a perfect circle, with Earth in the exact center, it would always be the same distance away from us but, with an ellipse, its distance is constantly varying.  Sometimes the moon is as close as 221,500 miles or it can be as far away as 252,700 miles.  It all depends on where it is in its orbit but it is, on average, about 239,000 miles away.  So, you see why these “just right alignments” are not an every-month occurrence.

Okay, since shadows are such an important part of a lunar eclipse, let’s talk briefly about them.  Let’s say that it’s a full moon and you are standing in your front yard looking at it.  Where is the Sun in relation to you?  Why, it’s directly behind you but below the horizon.  Yes, just because you are standing there in the dark does not mean that the Sun has turned in for the night.  It’s still out there in space, blazing away.  In fact, it’s the Sun’s light that is shining onto the lunar surface, making it bright (the moon does not generate any visible light of its own).  You just happen to be standing on the night side of the Earth and behind you is a ginormous lamp, shining out in all directions in space.  When the light strikes the Earth, our planet is going to be casting a very long shadow out into space in the opposite direction from the Sun, just like you would cast a shadow when standing in front of a bright light source.  But the Earth is round, and the shadow it casts is going to be in the shape of a large cone.  This cone-shaped shadow has two parts.  The first is a dark central shadow that also forms a cone and is called the “umbra”.  The umbra is broadest near the Earth but tapers and gets smaller the further away from Earth it gets.  The second shadow is called the “penumbra”.  The penumbra is fainter and it becomes broader the further away it gets from the Earth.  Check out the accompanying diagram to get an idea of what I’m talking about.

KINDS OF LUNAR ECLIPSES

Lunar eclipses come in three different flavors, all depending on what kind of alignment celestial mechanics has given us for the night in question.  The kind of alignment we have also determines which part of the Earth’s shadow the moon will be moving through.  In a penumbral lunar eclipse, the moon passes through the outer of Earth’s two shadows.  These are not very interesting to observe, in fact, it can be very hard to tell that anything out of the ordinary is happening at all.  With a partial lunar eclipse, the kind that we will see on November 19th, part of the moon passes through the Earth’s umbra, the darkest shadow, and that can lead to some very obvious changes in the moon’s appearance.  Finally, a total lunar eclipse results when the moon is lined up just right, and close enough, the be completely inside the Earth’s umbra.  Due to the effects of sunlight filtering through the Earth’s atmosphere, we often see the moon turn a deep red color.  Total lunar eclipses are, without doubt, the tastiest of the three flavors.  But, as we shall see, partial lunar eclipses can be quite nice too.

WHAT YOU ARE SEEING AND WHEN TO SEE IT

In order to see this spectacle, you will either need to stay up into the wee predawn hours of November 19th or, go to bed early on the 18th and set your alarm.  Here’s are breakdown of the timing (CST):

• 12:02 AM: The moon enters the Earth’s penumbra.  Stay in bed, this part is not only not interesting, it’s invisible to boot.

• 1:18 AM:  Okay, things are now just beginning to get interesting as the moon begins to enter into the umbra, the darkest part of the Earth’s shadow.

• 3:02 AM: Get your camera ready, the moon is now as deep into the umbra as it will get, with only 2.6 % of the moon’s visible diameter left illuminated.

• 4:47 AM: Go back to bed, the moon leaves the umbra

• 6:03 AM:  I hope you are getting some sleep because the moon is now leaving the penumbra and there is nothing to see here.

This eclipse, all told, is a rather lengthy event (normally it would only take about an hour for the moon to drift completely into the Earth’s shadow).  Why is this one so long?  It’s because on this night, the moon is around 252,600 miles away and that means that it is moving more slowly in its orbit compared to when it’s closer to Earth.  Will the moon turn red?  No.  That happens when the moon is completely within Earth’s shadow and the light from the Sun that is being bent through our atmosphere has most of the bluer components scattered out of it, only allowing the redder portions to reach the lunar surface,  making it look red.  But take heart, the moon’s color will definitely change because it is deep enough into the umbra to see some of the filtering effects from our atmosphere.   This time, rather than a deep red, you will likely see the moon become a coppery color.  This will be a great photo opportunity so get your camera ready beforehand.

Let’s hope that we have clear skies during this time so that we can all get outside and look up together in both awe and wonder!

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What marvelous things our eyes are.  Of all the five senses, vision is perhaps the most important, with 80% of the information we obtain regarding the world around us coming entirely through eyesight.  Our eyes collect information about the size, shape, color, and texture of objects.  They permit us to have depth perception, judge distances to objects, as well as inform us whether an object is stationary or moving.  If the object is moving, our eyes let us know its direction and its relative speed of motion.  Our eyes also allow us to perceive the beauty of a sunset and pick up on non-verbal communication signals such as facial expressions or hand gestures.  Our eyes function in daylight as well as in darkness and, on clear, dark nights, we can stand rapt in awe as we gaze upon thousands of stars spread across the dome of the sky.

While our eyes function as light sensors, it is our brains that make sense of the information being fed to it.  As the light impinges upon the sheet of photosensitive tissue known as the retina, and located at the very back of our eyeballs, the light gets transformed into electrical signals, which are then sent along our optic nerve to the brain for processing.  In a very real sense, our eyes are the brain’s windows not only upon our immediate surroundings but to the Universe at large.  Your eyes are the most basic set of astronomy gear that you possess and for this month’s blog, I want to do something a little different by paying tribute to the eye.

WHERE’D YOU GET THOSE PEEPERS?

Most animals have functioning eyes (although there are some species that have secondarily lost or reduced their eyes over the course of evolution), and we know from the fossil record that eyes go as far back as 540 million years when, for reasons we still do not quite understand, complex multicellular organisms suddenly appear in a wide diversity of body plans and lifestyles.  Among this dazzling array of ocean dwelling critters were trilobites.  Resembling the modern-day terrestrial arthropods many of us know as roly-polys, pill bugs, or wood lice, trilobites possessed remarkably complex compound eyes.  Each individual component of their eyes had its own lens made of calcite that gathered information and passed it on to the brain which then formed a mosaic-like image of the trilobite’s immediate environment.

But eyes must surely have a longer history than this.  Unfortunately, the fossil record doesn’t reveal much information in this regard.  To fill in the gaps of the story, we must look to modern day organisms to provide us clues.  The simplest light detectors are to be found in single-celled organisms such as Euglena.  There are many kinds of Euglena but the one many of us are familiar with are the ones often found in ponds.  They have a whiplike structure called the flagellum, used to propel this unicellular critter through the water, and they possess both animal and plant characteristics.  For example, when behaving like an animal, Euglena will engulf food particles in a process known as phagocytosis and when they behave like plants, they can manufacture their own food via photosynthesis.  At the base of the flagellum is a light sensitive patches known as  a “stigma” or“eyespot”, which is incapable of forming any kind of image but is very useful in steering Euglena either away from or towards light.  Eyespots of one sort or another can also be found in more complex multicellular creatures such as jellyfish and flatworms.

Over time, a depression around the eyespots evolved, making the organism’s vision a little better by improving the ability to not only detect the direction of a light source but movement as well, an important advantage in the deadly game of predator versus prey.  Eventually there arose an organism that had the depression around their eyespots closed to a point, effectively becoming a pinhole camera of sorts.  Eyes became increasingly more sophisticated until, finally, there appeared the complex eyes of trilobites and many other arthropods (animals with chitinous exoskeletons, segmented bodies, and jointed appendages such as crabs, spiders, and insects).  But according to the fossil record, the evolutionary leap from these simple kinds of eyes to more complex ones like ours (i.e. with a sclera, pupil, lens, and retina) took only about 30 million years which, I hate to even say it, was a blink of the eye in terms of the long history of life on Earth.  For a long time, biologists thought that with so many kinds of eyes and ways of seeing, that vision must have arisen independently within several different lineages of organisms.  But recent studies in genetics and biochemistry have revealed that all these different ways of seeing share a group of light sensitive proteins known as “opsins “ which strongly suggests that eyes have a common ancestry.

I don’t want to give the wrong impression that evolution proceeds towards specific goals or endpoints, it has no direction whatsoever, no matter how it may appear in hindsight as we look through the fossil record.  Evolution is the change brought about by the inherited traits of a population of organisms over time and, as such, the process is blind with no ultimate or proximate goals in mind.  So, don’t get the idea that the human eye is the pinnacle of evolutionary perfection because there are many examples throughout the animal kingdom of eyes that far outmatch our own.  Eagles for example can see quite clearly for about eight times as far as your eye can, allowing them to spot a rabbit, camouflaged in its surroundings, two miles away.  Dragonflies have as many as 30,000 facets in each eye and they can see polarized and ultraviolet light, forms of light invisible to our eyes.  Mantis shrimp possess some of the most remarkable eyes in the animal kingdom.  Their eyes are composed of tens of thousands of individual elements allowing them to perceive the world through 12 channels of color along with UV and polarized light.  The human eye can process only three channels of color: red, green, and blue.   The largest eyes in the animal world are said to belong to the colossal squid (Mesonychoteuthis hamiltoni).  These squid have eyes that are the size of soccer balls, making them efficient light collectors, allowing the squids to detect the movement of prey, as well as predators such a sperm whales, in total darkness as they eke out their living at great depths in the Southern Ocean.

THE HUMAN EYE AND STARGAZING

As your eyes take in the world around you, the information that they are gathering comes in the way of photons, those discrete quanta of light that behave as both particles and waves.  Objects may be emitting photons, like a light bulb for example, or reflecting them, like the photons being emitted by the light bulb are bouncing off various objects in a room.  Physicists recognize four fundamental forces in nature: the gravitational force, the weak nuclear force, the strong nuclear force, and the electromagnetic force.  Each of these forces has a carrier force particle associated with it, which act as the method by which a given force transmits itself to other particles they are affecting.  We won’t go into too much depth here but just know that photons are the carrier force particle for all forms of light, otherwise known as electromagnetic radiation.  The forms of light in the electromagnetic spectrum range from short wavelength, high energy gamma rays and x-rays to longer wavelength, low energy radio waves and microwaves.  The human eye has evolved to only perceive a very narrow sliver of wavelengths (and their associated photons) within the middle of the electromagnetic spectrum, namely wavelengths in the range of 380 to 720 nanometers (one nanometer is equal to one billionth of a meter).  We are blind to all the other varieties of light outside of these ranges and the ridiculously narrow section of electromagnetic waves that we can detect is otherwise known to us as “visible light”.  It is a testament to science and human ingenuity that we have invented detectors to act as supplements to our eyes to learn about a universe that broadcasts itself across the entire electromagnetic spectrum.

When we think about our vision or visible light, we often associate them with color perception.   When our brains tell us whether we are seeing blue or red all depends on the wavelength, or energy level, of the photons that are hitting the back of our eye.  Lining the insides of the back of our eye is a thin layer of tissue known as the retina.  The retina has two types of special photoreceptor cells: concentrated in the center of the retina are cone cells and around the periphery of the retina are the rod cells.  Cones allow us to perceive color and fine details while the rods allow us to see grayscales in low-light conditions.  Retinal cells also contain a variety of those opsins that I mentioned earlier, and each is sensitive to the array of photons with different energy levels and wavelengths.  As the photons bang into the retina, they generate an electrical impulse that then makes its way along the optic nerve to our brains, where the signal is decoded to register color and image detail.  Since color perception is highly subjective, it is difficult to put a firm and fast number on how many shades of color we can discern but it surely must be tens of thousands, with many researchers citing a million.

When it comes to stargazing it’s the rods that are running the show.  Cones work mostly during the day but if you are looking at a celestial object with a high enough illumination level, they can still contribute (i.e. Mars registers as an orange-red while, in a telescope, you can see the earth-toned belts of Jupiter, and bright stars such as Sirius and Betelgeuse show colors as well).  The key thing to know here is that as long as the object is capable of zapping your retina with a photon, you can, theoretically see it.  Stop and consider the implications of this: it doesn’t matter how small or how far away something is from you, if it can transfer a photon to your eye, you can detect it.

Step outside on a good, dark night and look at all of those stars overhead.  By just glancing at them you can’t really tell how far away they are, but they are placed at such tremendous distances from the Earth that astronomers must use a distance unit less cumbersome than miles or kilometers: the light year. One light year is the distance that a photon would travel in one year’s time through the vacuum of space.  That comes out to about 6 trillion miles.  The closest star system to Earth that you can see with the unaided eye is that of Alpha Centauri, relatively close at a mere 4.4 light years (using the fastest propulsion system we now have it would be a journey of many thousands of years before you could get there).  Compare that with Deneb, currently visible in our night sky within the constellation of Cygnus, and which lies at around 1,550 light years away. The most distant naked eye star puts even Deneb to shame.  It’s known as Rho Cassiopeiae and can be found in the familiar W-pattern of stars that make up the constellation of Cassiopeia.  Rho is estimated to be a whopping 8,200 light years away and even though it looks tiny and insignificant to your eye, you should know that its girth is 40% larger than the entire orbit of Mars around the Sun.  And this is an important consideration: most of the stars you can see with your unaided eye are larger than our own Sun, some of them with diameters measured in millions of miles (the Sun is just a bit shy of having a diameter of one million miles).  Even though they are many trillions of miles distant, they are still bright enough, given their huge sizes, to emit enough photons for the rods in our eyes to detect them.

All these stars that you see are to be found within our Milky Way Galaxy.  The Sun and all its family of planets, asteroids, and comets, comprise the solar system and virtually all the stars in our night sky are their own stellar system of planets and minor bodies.  Estimates of the number of stars in the Milky Way range from 100 to 400 billion and together we all exist within a single galaxy.  But there are many billions more galaxies in the whole shebang that we call the Universe.  They all lie at such tremendous distances from us that we cannot see them with the naked eye.  All but one that is.  Right now, if you go outside during these late summer and fall evenings, look off to the NE at around 10pm.  If your skies are dark enough and you know precisely where to look, you can just barely see a dim, fuzzy cloud of light.  This faint and fuzzy patch of light is the Andromeda Galaxy, and it is the most distant object that you can see with your unaided eye at some 2.5 MILLION light years away.  At that distance your eye cannot resolve the individual stars that comprise the galaxy and all that we can perceive is their total combined glow.  Think about that, the galaxy is quintillions of miles away and yet there are enough photons getting into your eye, having traveled for some 2.5 million years, before they smashed into your retina, got converted into an electrical signal, which your brain could then decipher as a faint cloud of light upon the sky.  And now, because you have read this (assuming you didn’t already know about it), your brain can allow you to put the sight into its proper context.  You’re welcome.

The rod cells in your retina use a photopigment known as “rhodopsin” and it is key to your ability to see in the dark and to perceive all of the awe and wonder of the night sky.  When you step outside at night from a brightly lit room and into the darkness, your eye begins to undergo a two-step process known as “dark adaptation” allowing you to see in the low light conditions.  The first step is purely physical, and it involves muscles that control the diameter of your pupils.  During the day, or in any kind of bright light conditions, our pupils close to a diameter of around 2mm.  This controls the amount of light entering the eye, too much light will damage the retina, hindering our ability to see or, in worse case scenarios, even blinding us.  But under low light conditions, the pupils will suddenly expand to gather as much light as possible.  In younger people the pupils will expand to as much as 7mm while in older folks like me, they will only increase in size to about 5mm.  This expansion of the pupils increases the amount of light entering the eye by a factor of some 10 times.

The dilation of your pupils is a response that occurs in seconds while the next step takes up to 20 minutes to complete.  This second step involves the retina and its rod cells.  After being in the dark for a long enough time, the rods begin to produce rhodopsin, the light sensitive pigment that makes your night vision work.  You may have noticed that upon entering a dark room after being in a well lit one, that you cannot see much of anything at first but, after awhile you slowly begin to make out the things in the room you might bump into and bruise your shin or stub your toe on.  The same thing will happen as you sit outside at night long enough.  After leaving the comfort of your brightly lit living room, the darkness outside can be intimidating because of the difficulty in seeing things.  But after a while, objects around you come into view.  If you are looking up when you first step outside, you probably won’t see anything but the brightest stars, but within about 15 or 20 minutes, you notice that the sky is filled with many fainter stars.  At this point, your dark adaptation is complete, and you are ready to take in the starry night in all its glory.  But whatever you do, do not let any bright light hit your eye.  Looking into car headlights, a flashlight, bright house, or streetlights, or even the bright light from your cell phone will destroy your dark adaptation in a second.  Why?  Because rhodopsin is a light sensitive pigment, and it has a threshold beyond which it will suddenly break down when exposed to enough light.  Astronomers are very sensitive about the use of bright lights at an observing site, and you can expect to get yelled at if you ever find yourself at such a location and you turn on your cell phone flashlight in order to see around.  The best way to preserve your night vision (and that of the cranky astronomers), and still see in the dark, is to use a red LED flashlight or, a regular old flashlight with red plastic film taped over the lens.  Why red light?   Red light has a longer wavelength and lower energy than does bluer light and the longer wavelength doesn’t really do any harm to the rhodopsin that your rods slaved over for 20 minutes to make.  Each time you let your eye get hit by bright light, the longer it takes to get dark adapted all over again.   And by the way, vitamin A is a precursor to rhodopsin.  Your body can convert vitamin A from beta carotene.  A great source for beta carotene is carrots.  Our mommas might not have always been right when giving out life advice but if yours ever told you to eat all your carrots so that you could see better, she was spot on.

Isn’t it amazing how those delicate globes of tissue stuck into the front of your skull, in combination with the firm 3lb mass of gray matter inside your cranium, conspire together to allow us to appreciate the aesthetic beauty of the night sky, ponder over what it all means, and to ultimately understand our place in a vast, ever-expanding universe?

The post September 2021 Feature – An Ode to the Eye appeared first on University Television - Comcast 61/1095 & UVerse 99.

The Perseid Meteor Shower is one of our most productive and popular showers and it peaks this year during the evening hours of August 11th and the early morning hours of August 12th.   The waxing crescent moon may interfere during the early evening, but it should only be a minor nuisance as it sets well in advance of when the shower really gets going.

WHAT IS A METEOR SHOWER? You can go out on just about any clear, dark night and see a few meteors throughout the evening. These are called “sporadic meteors”. Meteor showers are what happens when the Earth moves through a dense stream of sand grain-sized bits of debris left behind in the wake of a passing comet or asteroid. In the case of the Perseids, that comet is 109P Swift-Tuttle, a periodic comet with an orbital period of 133 years and that last came through the inner solar system in 1992. During a typical meteor shower, it is possible to see 10 or more meteors per hour.

HOW DOES A PIECE OF SPACE DEBRIS THE SIZE OF A GRAIN OF SAND BECOME SO BRIGHT?

Out in space, the bits of debris are called “meteoroids”. They travel around the Sun in various fairly well-defined paths and at various speeds. The fastest may be traveling at speeds of 26 miles per second. But once they get caught up within the Earth’s gravity well, they get accelerated to even higher speeds. The meteoroids that are responsible for the Perseids can get accelerated to speeds of 133,000 mph!

This tremendous speed means that the bit of debris has a lot of kinetic energy, the energy derived from their motion. Out in space, there wasn’t anything to slow them down, but once they slam into our atmosphere, it’s like they have hit a brick wall. They hit the air with such force, that they violently compress a column of air out ahead of them. The kinetic energy they carried goes into not only compressing the air, it also flash-heats the air column to thousands of degrees, ionizing the air molecules and making it glow. It gets so hot, that the debris is vaporized. The glowing streak of air is what we call a “meteor”, and it may only be a few feet thick, but several miles long. Typically, Perseid meteor streaks are produced at an altitude of about 60 miles up.

ANY CHANCE OF A METEOR HITTING THE GROUND?

Not likely. The bits of debris associated with the Perseids are very tiny and get completely vaporized before coming anywhere near the ground. Sometimes, larger bits of space rock do enter the atmosphere and pieces of them may survive long enough to reach the ground. If they do, we then call them “meteorites”.

WHERE DOES THE SHOWER NAME COME FROM?

If you were to trace back all the meteor streaks you see on a peak night, you would see that they all tend to radiate from one section of the sky. This point upon the sky is called the “radiant” and it indicates the general direction in which the meteor stream is located out in space. Astronomers name a meteor shower based upon the constellation or star the radiant happens to be nearby. In this case, it is the constellation of Perseus, legendary Greek hero who slew the Gorgon sister named Medusa.

HOW MANY DO YOU THINK I WILL SEE?

That’s difficult to say as there are so many variables involved. Every meteor shower comes with a proposed maximum hourly rate for the peak nights. In the case of the Perseids, that rate is about 60 to 80 per hour. But these are all idealized numbers that assume that a viewer is observing under absolute perfect conditions, which is extraordinarily rare.

One important factor as to how many meteors you might see whether or not you are on the night side of the Earth when it is moving through the densest portions of the meteor stream. If you are on the day side when that happens, you might not see as many as the folks who are lucky enough to have been on the night side.

Also, keep in mind that the Earth, and all the other planets, travel around the Sun in nearly circular orbits. So, let’s think of the Earth as a car driving down a highway in east Arkansas. At sunset, and into the early evening, when you look up at the sky, you are looking out the rear window. This is the Earth’s “trailing edge” relative to our direction of travel. But, after midnight, and especially before dawn, the sky overhead is like looking out the front window relative to our direction of travel. Where are we most likely to accumulate the most bugs on our vehicle? The front grill and windshield of course. Same with meteors. You may see a few meteors looking out the rear window during the early evening but it’s during the wee hours that you are likely to see the most. The morning hours is also when the radiant is highest in the sky.   However, you should be aware about the possibility of catching an “earthgrazer”, a bright fireball meteor that ravels horizontally across the sky as it skims through the atmosphere.  These tend to be long, slow, colorful meteors and you will not soon forget it if you are lucky enough to observe one.  Just bear in mind that they are relatively rare but are often associated with the Perseids.

An extremely important factor is where you are observing from. Unfortunately, most meteor streaks are rather faint, and you are not going to see any of them from a location that has lots of light pollution (light from buildings, advertising, streetlights, etc. that is wasted by not being properly shielded and is sent needlessly into the sky). To see the most meteors, you MUST be viewing away from light pollution and that often means traveling into the countryside.

OKAY, I LIVE IN A CITY, WHERE SHOULD I GO?

Here is a link to the Arkansas Natural Sky Association. Learn more about light pollution and make use of the site’s maps that guide you to other dark sky observing locations around the state: 

BUT I CAN’T OBSERVE ON THE PEAK NIGHTS, ANY CHANCE THAT I CAN SEE PERSEID METEORS OUTSIDE THOSE NIGHTS?

Yes! The nights on either side of the peak will provide you opportunity to see meteors but you will still see the most during the peak times.

ANY OTHER VIEWING TIPS?

• Dial back your expectations. It may be called a meteor shower, but that doesn’t mean that they are going to fall from the sky like rain. If you have near perfect conditions, then you might see a meteor every minute or two during the peak hours. Or, you might not see any. Sometimes it’s a crap shoot. You might stay up for hours and only have a few mosquito bites to show for it, but then again, you might get lucky by being in the right place and the right time and see the show of a lifetime. But, if you stay indoors, you won’t see any.
• Be patient. Sometimes there will be moments when the shower is active and then there will be lulls. That’s just the way it is, accept it. Carry along some music to keep yourself entertained during the wait.
• Let your eyes get dark adapted. This a process that can take up to an hour to complete. Once your night vision is in perfect working order, you will see more meteors. BUT, if you look at your cell phone, laptop, or any other kind of white light, even for a second, then your night vision is ruined, and you will need to wait another hour for the process to complete itself again. To avoid this, use a red filtered flashlight. The longer wavelength of red light is less destructive to your night vision. If you don’t have a red flashlight, just tape some red plastic film over a flashlight you have around the house. You can buy red plastic film that is used to repair broken taillights.
• Get comfortable with a blanket or sleeping bag on the ground or use a reclining lawn chair. The main thing you want to avoid is straining your neck. Expect to see meteors anywhere on the sky, don’t focus your attention solely on where the radiant is (which is in the NE).
• Have lots of water and snacks on hand.
• Dress appropriately. It can get chilly during the wee hours, especially if you are observing from a higher altitude. Be prepared for it.
• Pack the bug spray, this is Arkansas after all.
• Invite friends and family to join you, make it a party. Even if you don’t see many meteors, you can have spent quality time with people you love. Also, meteor showers can be inexpensive and romantic date nights. Just saying.

The post August 2021 Feature – The Perseid Meteor Shower appeared first on University Television - Comcast 61/1095 & UVerse 99.

If there is any other kind of celestial object that is capable of generating as much curiosity and wonder as a black hole, then I don’t know what it could be. Whenever I do just about any kind of astronomy outreach, with any age group, there is bound to be a question or two about black holes (although questions about the existence of aliens proves rather popular too). And I can relate to the enthusiasm folks have for these mind-boggling creations of Nature. At the mere mention of black holes, I become all giddy and will likely talk your ear off about them. In fact, a friend of mine has jokingly suggested that I should become equipped with a sign around my neck that says something to the following effect:

At least I think he’s joking. On second thought, he’s really not that good of a friend to begin with so who cares what he thinks, right?   Anyways, in this month’s blog, I want to tell you about black holes, what they are, how we know what we know about them, and where to look in the summer sky for the general areas in which two well known black holes are located. Obviously, by their very nature, black holes cannot be seen directly but it’s kinda cool to be able to point to an area upon the sky and say to yourself, “Yeah, THAT’S where a black hole is lurking right this very moment.” The coolness factor that comes from this month’s Night Sky blog entry is not from the actual “seeing” but in the “knowing”.

THE NATURAL HISTORY OF BLACK HOLES

A simplified working definition of a black hole is that it’s a region of space where matter has become so incredibly dense, and compressed into such a miniscule volume, that any object straying within a certain limit, cannot escape its gravitational pull. Not even light. With the first sentence of this article, I referred to black holes as being objects and here I just said that black holes are more a “region of space”.   In using the word “object” there is the implication that we are dealing with a solid body of some kind with a surface, like, say, a rocky planet. But black holes are definitely not an object in the classical sense. In the words of astronomer Janna Levin, in her excellent book, “The Black Hole Survival Guide”: “Black holes are nothing. Black holes are special because there’s nothing there. There is no thing there.”   How can nothing be a something with enough gravity to hold on to light, the fastest thing in the universe? For that matter, how can it wield any kind of gravitational influence upon something so seemingly insubstantial as light? Black holes have a way of making our puny primate brains go into conniptions in trying to understand them. They defy all our intuitive sense about reality and, well, they are just downright weird. In order to wrap our heads around what a black hole truly is, it will be helpful if we first talk a bit about gravity and how fast something needs to be moving in order to escape its influence.

In the year 1687, Sir Isaac Newton published his three-volume masterwork, “Principia”, where he lays out his laws of motion and his law of universal gravitation. According to Newton, gravity is a force of attraction between objects due to their masses. With enough mass, an object’s gravity can change the motion of another object by altering its direction, speed, or both. On top of that, Newton says that gravity is not just an attraction between an apple and the Earth but that it is an attraction that exists between all objects, everywhere in the universe. Gravity’s effect extends from every object out into space in all directions, and for an infinite distance. While its effects are boundless, it does weaken with distance as you move further and further away from a gravitational source. But how do you break free of its grip when you are close to that source?

Imagine you are standing on the Earth, and you’ve got a ball in your hand. You throw the ball upwards and, just as you expect, it comes right back down again. You throw it into the air again, but you add a little more “oomph” to it. This time the ball goes up higher, slows and then falls back to the ground again. Let’s say that you do this a third time, but you add a bit more special “oomph” to your throw. This time, the ball just keeps going and never falls back to the Earth. The technical term for your “special oomph” is “escape velocity” (if you want to talk like a rocket scientist) and it is the speed that an object must attain in order for it to break free of the gravitational influence of another body.

The two most important factors when considering an object’s escape velocity are a) the object’s mass and b) the distance to the object’s center. It’s a rather straightforward calculation that most high school physics students are taught using the formula v escape = 2𝐺𝑀𝑅‾‾‾‾‾√, where G= the gravitational constant (its numerical value is 6.67 × 10^-11 Newtons kg^-2 m²), M is the object’s mass, and R is the object’s radius. Once you do all the math, it turns out that the escape velocity of the Earth is 11.2 km/second. That’s how fast you must accelerate a rocket, a ball, or someone you don’t like in order to get them out of Earth’s gravitational grip and on their merry way into space.

Let’s say that the Earth was not as big as it is. Let’s say that this make-believe Earth has all the mass of the real one but only half the diameter. What’s the escape velocity now? Turns out to be 15.8 km/second.   Why is the escape velocity greater, even though the size is smaller? Well, it’s because we kept all of that mass inside a smaller body, making the make-believe Earth much denser.   When you decrease the diameter of an object and keep all the mass, you are much closer now to that object’s center of mass while standing on it’s surface and the gravity scales up in such situations.

We can go even more extreme than this. If you could compress the make-believe Earth down even smaller, say, to an object that is now 9mm in diameter, while still keeping all of the mass, the escape velocity would be the speed of light, 299,472 km/second. Shrink it down a smidge more and the escape velocity exceeds the speed of light. Either way, if you get trapped in the gravitational grip of such an object, you aren’t going anywhere, ever, because nothing in the universe can travel faster than light can. If you’ve been paying attention, you are probably asking yourself, “if photons of light do not have mass, then how can gravity have any effect on them no matter what the escape velocity is?” To answer that, we must recognize that so far, we’ve not been dealing with a complete picture of gravity. To resolve this issue, we must turn to Albert Einstein and his version of gravity as revealed to us in the theory of general relativity (GR).

General relativity states that gravity, rather than being a force of attraction, is actually the direct result of space becoming distorted by massive objects. We won’t go into how he arrived at this startling revelation but suffice to say, it was the great man’s crowning achievement in an already illustrious career. Einstein tells us that both space and time are an interwoven, flexible fabric called, shockingly enough, “spacetime”. When massive bodies like stars, planets, moons, or black holes interact with spacetime, they create depressions in it. These depressions in spacetime are called “gravity wells”, which then draw nearby objects into orbit around them. As kooky as it may sound, it’s quite real and verifiable. In fact, it’s been verified over an over again with countless tests for well over 100 years now and it is now our modern understanding of how gravity works. As American physicist John Wheeler (who also coined the name, “black hole”) has said, “Space-time tells matter how to move; matter tells space-time how to curve.”

And here at last is our explanation for why light, or anything else, cannot escape from the grip of a black hole once it gets caught in a gravity well. Light wants to travel in a straight line. Black holes, being such incredibly dense, compact objects, create gravity wells so deep, that any light or matter that gets funneled into it plunges over an abyss with sides so steep, nothing ever gets back out. Ever. Kids, this is why you should never play near a black hole. Also note, black holes do not suck things into them like cosmic vacuum cleaners, gravity just doesn’t work that way. Also note that because light cannot escape, we say these things are “black”.

Black holes did not immediately leap out of Einstein’s complex mathematical equations describing GR, but they did emerge pretty quickly and not from Einstein. Shortly after he published his theory of general relativity, he received a letter from a German astronomer named Karl Schwarzschild, saying that he had solved the equations and that, buried deep in all the math, was something rather curious.   Schwarzschild told Einstein that, using his field equations, it was possible, at least mathematically, to have a very dense, compact object, where, if other objects fell into their gravity well, they wouldn’t fall back out again. He even calculated a spherical zone around such a hypothetical object from which light itself would become forever trapped. It was at this point that we have the first theoretical model for our modern concept of black holes. This no trespassing, spherical region around these objects is now called the “Schwarzschild Radius”. It’s also called the “event horizon”, because information about any event happening beyond that “horizon” can never reach those of us on this side of it. Crazier still, beyond this point, Einstein’s math breaks down entirely. Or so it would seem. Work the equations and it says that all matter beyond the event horizon gets crushed down to an infinitely small point that we call a “singularity”. Anytime your math tells you that you have arrived at an infinity, it means that your understanding of whatever it is you are trying to describe is not yet complete.

Einstein himself dismissed all of this nonsense as just taking the math too far. He firmly believed that nature would have some way that would prevent all of those atoms comprising the mass of an object from ever being crushed down to a point where an object like a black hole would ever form, let alone to an infinitely small point. Nope, Einstein reasoned, nature would just not let a lot of matter be crushed into nothingness, leaving behind such a weird monstrosity of gravity. It just all sounded so gosh darn crazy. So, for many decades, the concept of black holes languished as mere mathematical oddities, fodder for science fiction perhaps, but not for real science. To cut this already long story short, physicists began to understand that yes, nature could find a way that would allow matter to get crushed right out of existence and leave behind a black hole: the catastrophic core collapse of massive stars.   For most stars, death arrives when the core runs out of fusible material and gravity does crush the core down to something smaller. But, at the quantum level, nature has a built-in safety mechanism that keeps gravity from crushing it right out of existence. Not so with dead stellar cores with 3x or more the mass of the Sun. In such situations, there is no stopping gravity and matter can in fact get squeezed down into nothingness. But how could we find the evidence? How could we see what is, by definition, unseeable? Well, black holes might not emit any kind of radiation from beyond their event horizons, but all of that gravitational clout is bound to interact with their immediate environments in some way. Our only hope in learning whether or not black holes were real lay in figuring out how they might interact with their surroundings and what sorts of clues we might detect that would give away their otherwise invisible presence.

Without further ado, allow me to introduce our two featured “stars” for this month’s blog edition: Cygnus X-1, a black hole in the constellation of Cygnus the Swan and Sagittarius A* (pronounced as “Sagittarius A-star), or Sgr A* for short, a giant black hole located at the center of our Milky Way Galaxy.   Read on and you’ll learn things like how we discovered them, where to look in the sky in order to find the general direction in which they are located, and some of the weird things that would happen to you should you be so bold, or clumsy, as to fall into one.

Today, we know that black holes exist all across our night sky, but Cygnus X-1 is rather special because it is the first confirmed black hole ever found. In 1964 a series of sounding rockets were sent into suborbital flights and carrying a payload of fancy Geiger counters. Those Geiger counters detected an unusually bright source of X-rays located in the direction of the constellation of Cygnus the swan. Astronomers, focusing their telescopes upon this region, found a massive, hot, blue O-type star. This was a bit weird. Even though O-type stars are rather luminous and very powerful, they just don’t crank out light in the X-ray part of the electromagnetic spectrum this brightly. Analysis of the star’s light showed a very strong Doppler shift, indicating that there was something invisible the star was orbiting around every 5.6 days. The only possible thing that could be invisible, emitting X-rays this strongly, and capable of slinging a massive star around it every 5.6 days is a black hole.

A paper published earlier this year indicated that Cygnus X-1 is located 7,200 light years away and weighs in at 21 times the mass of the Sun. That’s big for a stellar mass black hole which form when giant stars run out of fuel within their cores. When that happens, the star can no longer emit the energy needed to keep gravity from crushing it down into something smaller. The star’s outer layers come crashing down onto the core, bounce off, creating a shockwave that blows the outer layers away in a supernova explosion, followed by the core collapsing down into either a neutron star or a black hole. The core’s eventual fate is determined by the progenitor star’s initial mass and how much it lost over the course of its life. The new study indicated that the star that gave birth to Cygnus X-1 must have been a monstrous 60 times as massive as the Sun. Such stars would normally have lost a considerable amount of their mass before dying so accounting for Cygnus X-1’s weight is still a mystery.

Now, about those X-rays. As Cygnus X-1 and its massive stellar companion orbit around one another, the black hole siphons off material from the star and pulls it into a swirling disc around the black hole’s equator.   It’s called an “accretion disc” and it is shredded matter that is swirling around the black hole like water about to go down your bathtub drain. Except that this material is spinning at a significant percentage the speed of light. The inner portions of the disc are spinning faster than the outer portions and all of the friction from this motion heats the disc up to the point where it glows in X-rays. Hot, hot, hot! The black hole itself is spinning at some 800 revolutions per second, creating powerful magnetic fields that focus two jets of material outwards along the rotation axis of Cygnus X-1. Can you imagine what a sight that would be! Provided of course you were watching from a very safe distance.

Kids (and many adults) are curious about what might happen if they were to fall into a black hole and I’m always more than happy to oblige them with all of the gory details.   So, let’s say that you were an astronaut and somehow or another, you strayed too close to the black hole, and you got pulled in. It’s not going to be pretty. Let’s also say that you are going in feet first. You would begin to feel a tug on your body of course but the tugging will be stronger at your feet than at your head. That’s because your feet are closer to the gravitational source than your head. At the same time that you are feeling stretched, you will also feel squeezed. The upshot of all this is that tidal forces of Cygnus X-1’s gravity is going to stretch you like taffy. Every. Square. Inch of you, right down to your constituent atoms. You only have to look at what it’s doing to that star in order to get an idea as to what is about to happen to your body. For those of us watching from a safe distance, we would literally see you stretched out into something that looks like spaghetti (and the actual technical term for all this is “spaghettification”). I’d say, send us a post card and tell us what’s on the other side, but you would be dead before you even hit the event horizon.

LOCATING CYGNUS X-1

During the month of June, the constellation of Cygnus is best seen around midnight while facing the NE. The swan appears to be flying along the summer Milky Way. It will rise earlier and earlier throughout the summer and will be on display well into the fall. Use a star map or app to locate the familiar pattern of stars that form the Northern Cross asterism. Cygnus X-1 is located about 1/2 a degree away from the star Eta Cygni.

SAGITTARIUS A*

On average, most stellar mass black holes are anywhere from 3 to 10 solar masses but within the hearts of most galaxies, there are black holes that seem to be on steroids, supermassive black holes. These Godzilla black holes range from millions to billions of solar masses. Holy cow, where did they come from? We don’t know. No star gets so big as to be the progenitor of something that massive. It’s an ongoing area of research in astronomy and we just aren’t sure if they could have arisen from out of the collapse of a massive cloud of gas and dust or if they form by the mergers of smaller black holes or neutron stars (or both). You would think that there would be black holes that are intermediate in mass between stellar mass and supermassive but they seem to be few and far between. Astronomers have been diligently searching for them but have only recently found convincing evidence for their existence. Whatever the solution is to their origins, just know that there is one in the center of our own galaxy that has a mass of 4 million Suns. By comparison, the black hole that was imaged in the galaxy M87 a couple of years ago has a mass of some 6.5 billion Suns.

The idea of supermassive black holes at the center of galaxies was first proposed back in the 1960’s but finding one at the center of the Milky Way Galaxy was problematic due to all the intervening dust and gas that obscures our view towards galactic central. However, by imaging the core of our galaxy at infrared wavelengths, which can penetrate all that gas and dust, astronomer Andrea Ghez was able to map the orbits of stars that all appeared to be moving around something very compact and invisible. There is nothing we know of in the universe that can slingshot dozens of stars around in their orbits like that except for a supermassive black hole. After many years of painstakingly accumulating data, Andrea provided overwhelming evidence for their existence, something many of her peers and academic advisors over the years told her would be impossible. She won the 2020 Nobel Prize in physics for her efforts. Don’t let others deter you from your goals!

What happens if you fall into a supermassive black hole? Well, it’s still ultimately not good but at least, theoretically, you might live a bit longer than you would falling into a stellar mass black hole. Stellar mass black holes have much stronger tidal forces than does the supermassive variety. Remember when we were talking about escape velocity, and I said that one of the things that determine how powerful the grip of gravity is going to be for any object is how far away you are from the center. Well, with a stellar mass black hole the radial size of the event horizon might be just a couple of miles or less. For a supermassive black hole, that radial size might be 7.3 million miles. Falling into the stellar mass black hole, the tidal forces are going to be much, much stronger because you are allowed to get closer to the center before passing the event horizon, but they are much weaker for a supermassive black hole. The gravitational forces are still going to be powerful enough to pull you in at speeds approaching that of light.   Now, with Einstein’s theory of special relativity, when you travel at such speeds, time will literally slow down for you. This is known as “time dilation”. Einstein also says in his theory of general relativity, that time dilation occurs the closer you are to a gravitational source. It may sound crazy but it’s true. We have to factor in the effects of time dilation in our GPS satellites as they orbit the Earth, if we didn’t all your GPS devices and apps that make use of them would be worthless.

So, as you reach the event horizon, those of us on the outside, would (theoretically) see your image freeze upon its “surface”. To you, you would just go on through but, to our eyes, you appear to be stuck. Eventually, our image of you would get redder and redder as the photons reflecting off of you lose more and more energy. After some time, your image would just fade away. But as you fall inwards, there are things out ahead of you that have been experiencing time dilation for much longer than you have. You would be able to see everything that has fallen into the black hole in the past. Looking behind you, you’ll see everything that ever will fall into the black hole. In essence, you will be able to see both forwards and backwards in time and I’m not sure if that’s just cool or utterly terrifying.

LOCATING SAGITTARIUS, A*

Sgr A* is some 26,000 light years away and its location is hidden by gas and dust but you can get a good idea of the direction in which it lies by following the flight of Cygnus the swan along the path of the Milky Way. Near the horizon, locate the asterism known as “The Teapot”, in the constellation of Sagittarius. Just above, and to the right of the teapot’s spout is the direction in which to find galactic central and Sgr A*.

I hope you’ve enjoyed our foray into black holes and that you have learned a bit more about them. If you want to learn where even more black holes are throughout the entire year, then visit the NASA Night Sky Network to find easy to read, printable star maps of their various locations:

For me, just knowing where black holes are in my night sky fills me with both awe and wonder with the universe.

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