Weekend Sky Report

The planet Venus has been confused as an airplane, a helicopter, even a UFO. Emergency dispatchers have fielded 911 calls reporting a silent, floating light in the sky. It’s easy to understand why Venus is so often confused as something else. Since it’s between the Earth and the Sun, it always hugs our horizon, just like a distant aircraft. And it’s the second-brightest object in the night sky behind the moon. Venus is 15 times brighter than the brightest star in the night sky, Sirius. And planets don’t twinkle like stars do. Stars are single points of light in the sky, so their light is very susceptible to atmospheric distortion. But planets are nearby objects reflecting light from the Sun. You can zoom in on planets and see their structure pretty easily with modest backyard telescopes. So why not try that out with Venus?

These days, Venus is in the Western sky in the early evening. Go out before 8:30--anytime after that, you’ll need a more unobstructed view of the horizon. If you have a telescope, get it out. You’ll notice that you don’t see a perfect circle the way you would if you looked at Mars or Jupiter. Because Venus is closer to the sun, we can only see the portion that’s illuminated by the sun. Right now, Venus will look like a gibbous moon. By mid-April, 2020, Venus will reach its highest point in the evening sky and will look like a quarter moon through a telescope. After that, it will look like a crescent until it disappears from the evening sky until late Spring of 2021.

The Local Group of galaxies includes over 30 galaxies within about 10 million light years of our own Milky Way galaxy. The three largest galaxies in the local group are: The Andromeda Galaxy with about a trillion stars… our own Milky Way with anywhere from a hundred to 400 billion stars… and this weekend’s target… the Triangulum Galaxy—weighing in at around 40 billion stars.

The Triangulum Galaxy gets its name from the constellation where it’s found. It’s a small constellation and, as the name suggests… it’s a triangle. But it’s a very acute triangle… it’s long and narrow. Tonight around 8pm it will be almost straight up in the sky. Face the west, then look straight up in the air, then down slightly. Look for the star at the point of Triangulum, then find Mirach—the bright orange star in the center of the constellation Andromeda. Draw a line between those two. Scan toward the center and just below that line and you should find the Triangulum Galaxy.

Now, as I said before, it’s one of the most distant objects you can see with the naked eye, but suburban observers like myself don’t have a prayer of seeing it without help. It’s only visible to the naked eye under VERY clear, VERY dark skies. So grab some binoculars or a telescope. When you find it, it’ll look kind of like a dim, fuzzy blob. But if you’ve got a good telescope, you may notice that it kind of looks like a pinwheel… but don’t confuse it with Messier 101, also known as the Pinwheel Galaxy… we’ll save that one for another time.

Stars form in huge clouds of gas and dust that some astronomers call “Stellar Nurseries.” The gas accretes or collects together, and as that body gains mass, its own gravity then causes it to collapse in on itself. Once there’s enough matter there, nuclear fusion begins, and a star is born. And much of what we know about star formation, we learned by studying the nearby Orion Nebula.

The Orion Nebula is just over 1300 light years from our solar system, and it’s believed to be an enormous 24 light years across. Because it’s so big, and... relatively close, it’s easily visible with binoculars or a telescope, even under fairly bright, suburban skies.

You can find it high to the southeast around 9 o’clock all this weekend. Just look for the three stars that make up Orion’s Belt, and look below it for what looks like a smaller collection of stars. In the middle… is the Orion Nebula.

Now, to you, it’ll just look like a fuzzy cloud around a few stars. But most photos you’ll find of the Orion Nebula are full of brilliant colors and detail. That’s the result of long exposures, or specialized equipment observing wavelengths we can’t actually see. But because astronomers are able to use those tools, we’ve learned so much about how stars are formed.

Saturday night is the official full moon, but it’ll pretty much look full all weekend. It rises just after sundown, so it’ll be low on the southeastern horizon in the evening after dark. Often, this can make the moon look bigger, but it’s actually the same size in the sky as if it were straight overhead. A moon low on the horizon can also have a color like yellow, orange, or red. The reason for that is the same reason the sun seems to change color at sunset or sunrise… it’s seen shining through many more layers of atmosphere than if it were higher in the sky. So depending on the conditions, the moon can take on a certain hue.

All that aside, looking at a full moon through a telescope, you notice a lot. The craters, the so-called “seas,” the “Ocean of Storms—“ that’s the big sea… So just what are all those geographic features?

Well, the craters are pretty self-explanatory. They’re impact craters from the eons of the moon’s existence. Some of them are bigger than others, and some have some unique features. Take the Tycho crater. It’s the big one in the southern hemisphere with what looks like lines spiking off of it. That’s impact ejecta. Whatever made the Tycho crater was big enough to spray rock and dust so far across the moon’s surface that we can easily see it from Earth. And we know from samples taken on the Apollo 16 mission that Tycho is a relatively young moon crater, having formed an estimated 108 million years ago. Compare that to the much older “Seas,” which are left over from a time when the moon was geologically active. They’re vast plains of volcanic basalt—basically lava flows.

So take a moment to appreciate the full moon this weekend. Howling is optional.

Around 9pm, look low to the southeast to find the brightest star in the night sky. Bright white, twinkling Sirius. Above it, you’ll see that iconic winter constellation Orion the Hunter. The orange star at his shoulder is the red supergiant Betelgeuse. Draw a line between Sirius and Betelgeuse, then look to the left, or east to find Procyon (PRO-see-on), another bright white star, and there you have it. A large, nearly perfect equilateral triangle of bright evening stars.

Now Procyon is pretty close—just over 11 light years away. But Sirius is even closer at just 8.5 light years away. The fact that they’re so close helps to explain why they’re so bright. But by most estimates, Betelgeuse is over 500 light years away. And its orange color indicates that it’s much cooler than the other two stars. So why is it so bright?

There are a lot of reasons, but one is that it’s ENORMOUS. If you were to put Betelgeuse where the sun is, it would engulf the orbits of all four inner planets, the asteroid belt, and by some estimates, even Jupiter.

And Betelgeuse has been getting a lot of attention lately not because of how bright it is, but how dim it’s getting. This has some astronomers speculating whether the star is collapsing, which could result in its ultimate demise… a supernova which would be as bright as the full moon and visible in the daytime for months. But not so fast… Betelgeuse has been known for centuries to vary in brightness for a number of reasons. This is just one unlikely explanation among many others… but it is probably the most fun.

Betelgeuse, the right shoulder of Orion the Hunter, which is prominent in the eastern sky this evening, is a truly remarkable star. For one thing, it’s one of the largest stars we’ve ever discovered. If you were to replace the sun with Betelgeuse, it would engulf all four inner planets from Mercury to Mars, and, by some estimates, even Jupiter. It’s enormous.

Now, in the celestial world, typically the bigger the star, the shorter the lifespan. Our sun is about 4 and-a-half billion years old. Betelgeuse is only estimated to be 8-and-a-half million years old. And yes, it may go supernova in our lifetime... or it could take up to a million years... we simply don’t know.

What we DO know is that WHEN Betelgeuse goes supernova, it will easily be visible in the daytime, maybe even outshining the full moon.

Lately, astronomers have noticed a significant dimming of Betelgeuse. What was once considered to be the brightest star in Orion is now just another point of light in the sky. But this change isn’t unprecedented. Betelgeuse has long been known as a variable star, meaning its brightness is known to change. But dimming this significant could also mean that big changes are happening 650 light years away. It could be collapsing, eventually resulting in a supernova… or other forces may be at work. We simply can’t know for sure. But even though it will mean one of the brightest stars in the night sky will be gone forever, it won’t be a time for mourning. Because if we DO get to see it, we’ll be witnessing one of the most significant and spectacular celestial events in human history.

At 2300 light years away, the cluster resembles an upside-down Christmas tree with the brightest star representing the base of the tree. The other stars form a loose cone shape that makes it look like Christmas tree lights.

The Christmas Tree Cluster is the more luminous part of a larger area designated as NGC 2264. This area also includes the Cone Nebula, Snowflake Cluster, and the Fox Fur Nebula. But most home telescopes will only be able to see the Christmas Tree Cluster. In fact, even a pair of binoculars or a small, hand-held scope should reveal the cluster… if you know where to look.

To find it, look to the East after 8pm. If you have a good view of the Eastern horizon, you’ll notice the bright star Procyon in Canis Minor. Trace a line between bright white Procyon and bright orange Betelgeuse, the right shoulder of Orion. Find the center of that line and scan upward with your telescope until you see a small cluster of brilliant blueish stars. That’s it. The Christmas Tree Cluster.

When you find it, you’ll be looking at not only the cluster itself, but also the nebula where it formed. If you have appropriate filters, a big enough telescope and are under clear, dark, rural skies, you may see some of that surrounding nebulosity.

The constellation Auriga is home to the bright star Capella, also known as the Harvest Star, which can be seen even under urban skies. But you’ll need to be away from the city to view this weekend’s targets.

Auriga is home to three Messier objects, named after 18th century French astronomer Charles Messier, famous for his catalog of deep-sky objects. The three objects are all open clusters, which can be seen through most backyard telescopes.

To find them, find Auriga. It’s a large constellation that’ll be in the northeastern sky in the evening. Again, the best way to find it is to find its brightest star, Capella. The rest of the constellation forms a hexagon below and to the right of Capella.

The three open star clusters within it are M36, M37, and M38. Let’s work from the inside out. The cluster furthest within Auriga is M38. It’s also known as the Starfish cluster. To find it, find the two stars opposite Capella. Elnath, and Theta Aurigae. Make a near right triangle inside the constellation, and find the inside angle. Scan down slowly until you see a faint cluster of stars. That’s M38. Scan further and you’ll see M36, which looks similar, but less compact and a little brighter. Scan outside the constellation between the same two stars and you’ll find M37, which is the brightest of the three, and considered one of the finest star clusters visible in the night sky.

The three stars that make up Orion’s belt is the giveaway. But there’s a lot more to appreciate. Like Rigel... Orion’s bright blue left foot. Rigel is an enormous, hot star that’s actually part of a system of 3 to 5 stars, but we can only see the biggest, brightest one--Rigel A. Rigel is 20 times more massive than the sun, 80 times bigger, and tens of THOUSANDS of times brighter. It’s also young... only around 9 million years old.

But the biggest star in Orion is his bright orange right shoulder, one of the largest stars we know of. Betelgeuse. Betelgeuse is so big that if we were to swap it with our sun, its surface would reach beyond the orbit of Mars.

Now you don’t need a telescope to appreciate the brightest stars of Orion, but I’d get it out anyway… because the Orion Nebula has hooked so many people on astronomy. You can see it with almost any telescope. And we’ve learned a lot from it. The Orion Nebula is a stellar nursery. New stars form there from collapsing clouds of gas and dust. And almost everything we know about stellar nurseries came from studying the Orion Nebula. If you make a triangle with the center of the belt, Rigel, the left foot, and Saiph, the right knee of Orion, the nebula is right in the middle. You can’t miss it.

First, what is a globular cluster? A globular cluster is a densely-packed group of stars bound by their own collective gravity. They form gradually—many of them over literally billions of years—pulling new stars in as they complete their orbits around their host galaxy. The globular we’re looking for tonight is Messier 15—also known as the Globular Cluster in Pegasus.

To find Pegasus, look high to the southwest around 8pm. Find the nose of Pegasus, the orange star Enif, which is also the brightest star in Pegasus. Then, through your telescope or binoculars, scan just to the right, and slightly downward. When you find what looks like a fuzzy star, you’ve found it. A 12 billion-year-old collection of well over 100,000 stars… that’s over 170 light-years across.

What sets Messier 15 apart from a lot of other globular clusters is that it’s theorized to have an intermediate-class black hole at its center. This type of black hole has only been discovered in the last 15 years. Before that, all we knew about were stellar-mass black holes—the small ones, and supermassive black holes—like those found at the center of galaxies. And while we don’t yet know for sure whether there’s one in Messier 15, it’ll be fun to ponder as you look at it tonight.