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The December 2020 Sky: Gifts from Space Part 1 Video Transcipt

Looking at the night sky from here in North Georgia on December 21 a little after sunset at 6:30 p.m. We’re facing East, so the bottom edge of our view here is the eastern horizon, and you can see the northern horizon on the left edge and the southern horizon on the right edge. Things towards the middle and the top are things that would be overhead at the top of the sky. And what we see is a sky full of stars. Stars form patterns on the sky called constellations. Constellations are areas of the sky. They’re kind of like states on a map. Anywhere you point on a map of the United States, you point within the borders of a state, and anywhere we point on the sky, you point within the borders of a constellation. These are the borders of the constellations that are up now, and the first constellation that we’ll look for is called Taurus, the Bull. We look for a v-shape of stars to find Taurus, that’s the head of the bull. We’ll put up an outline. It’s kind of on its side here, and there’s two stars away from the v-shape that form the ends of the horns for the bull. Put up a picture so we can see Taurus the bull a little bit better there.  There’s a bright orange star that’s the bull’s eye, known at the eye of the bull: Aldebaran.  ldebaran sort of stands out compared to the rest of the bull’s head, and that’s for a good reason. It’s a star that’s in the foreground. It’s in front of the other stars that form the v-shape of the head of Taurus the bull. They are a group of stars called the Hyades, a star cluster.  So stars that actually formed together in space in the same region. We’re going to take a closer look at Taurus so we can see the Hyades a bit better. So now we see the Hyades a bit better towards the bottom edge of the screen there, a sort of spattering of stars that formed together from one cloud of gas in space, near each other. They are all around 150 light-years away, so that means the light we see from these stars took 150 years to travel to us. Now this is relatively close compared to how big our galaxy is, even it might sound like a long time, and we can see that if we compare the Hyades to another star cluster just above it called the Pleiades.  So a little more towards the top center you’ll notice a maybe more distinctive cluster of stars that is called the Pleiades or the seven sisters. It’s a bit further out. It’s a little over 400 light-years away, and so seeing it at a further distance the stars appear a little more concentrated in our sky. It’s easier to pick it out as a cluster of stars that formed together in space. Now in Greek and Roman mythology, the Pleiades were the seven sisters, beautiful daughters of Atlas, a titan, and the sea-nymph Pleione, but actually they had more sisters. Their half-sisters were the Hyades, so the Hyades star cluster were also daughters of Atlas, and the Hyades were associated with rain and stormy weather for sailors. Let’s zoom out and look for some more constellations. Our next constellation is high in the sky to the north, so we’re going to turn our view so that we’re facing north. That will put the northern horizon at the bottom of our screen, and there’s a constellation high in the sky that’s found by looking for a zigzag shape of stars. The constellation is called Cassiopeia, and in Greek and Roman mythology Cassiopeia was a queen, a beautiful queen seen sitting on her throne here. Now she was said to boast far too much, and so she was cursed to circle the sky forever. So all stars appear to rise and set as the Earth turns, and they appear to be turning around a star called Polaris. Polaris is also called the North Star. So you’ll always find it to the North. It’s the only star that’s not moving around in the sky because it’s right above the North Pole of the Earth, and so Cassiopeia there will appear to circle Polaris throughout the night and as well as throughout the year. And she’s actually circumpolar so that’s where this idea comes that she’s caught circling around in the sky forever because she actually doesn’t set below the horizon from most places when you look at Cassiopeia in the northern hemisphere. Now there are different cultures around the world that had their own constellations, their own pictures and stories about the sky. So while ancient Greeks and Romans saw these stars of Cassiopeia as a queen, people that lived in Siberia saw the same five main stars of the zigzag as five reindeer. Unfortunately not magical reindeer that could fly, instead they were regular reindeer that were said to be wading in a river. And so the river is actually across the sky as well. I’m going to brighten it so we can see it better. It is the Milky Way. The Milky Way is our own galaxy. We live in a spiral galaxy. It has a flat disk made out of clouds of gas and dust and stars, and it’s flat like a pancake. It has spiral arms across it, but we don’t see those here because when we see the Milky Way in the sky what we’re seeing is a side view, an edge view of that pancake of stars running across the sky. We’re actually going to take a look at a really cool sight that’s going to be along the western horizon. So we’re going to turn the sky again, sort of follow the Milky Way across to the west there.  So we’re facing west, and between south and west you will find a very bright object. It’s actually not one planet, but two, right on top of each other on December 21 just a bit after sunset. Now I’m only showing the label for Jupiter because the label for Saturn would just appear right on top of it.  It’s Jupiter and Saturn that are going to be lining up in a conjunction. Now Jupiter is much brighter than Saturn and it will dominate the light that you see from these two planets, and it’s actually great to start watching this conjunction now because the planets are drawing closer and closer together in the sky. If you look towards about south-west just after sunset you can watch them each night as they move closer together. And it’s on the 21 that they’ll get to be their closest. The planets are all going around the Sun just like we do, so they move around in the sky regularly. You find them in different places from month-to-month and year-to-year, and Jupiter and Saturn have a conjunction, they appear to line up in the sky, about every 20 years. So the next one won’t be until 2040, and this year’s is actually particularly close.  It’s going to be within about a tenth of a degree of each other. That’s about one fifth as wide as the full moon, so they’ll appear very close in the sky. In fact, if you have a small telescope, that’s one of the best ways to look at this on the night of December 21 is to set up the small telescope and point at these two planets. And you’ll be able to see both of them in the same view. So let’s take a look at that here in the planetarium. We’re going to zoom in on Jupiter and Saturn. So we’re zooming in kind of like we’re looking at Jupiter and Saturn through a small telescope. And you’ll see here there are a few dots of light, very small dots of light right around Jupiter and Saturn, and some of those are moon of the two planets. We can find Jupiter’s largest moons. It has four largest moons called the Galilean moons. However, on the night of the 21, you may only be able to see three of them, it depends on when you’re looking. Those moons  are going around Jupiter, so they move their positions, and sometimes they might be in front or behind Jupiter. And we also have the largest moon around Saturn might be visible as well, depending on how much detail you can see with your telescope, and that’s Titan. And you’ll also, of course, see the beautiful rings around Saturn. We’ll zoom away. There’s more than planets going around the Sun. We also have asteroids. Those are going to be rocky bodies, but they’re much smaller than planets, and there’s thousands of them going around the Sun. One asteroid seen earlier this year in April, it made news because it looked like it was wearing a mask. Let’s take a look at the picture of an asteroid called 1998 OR2. So here’s the image of the asteroid that was in news articles because it kind of resembles a mask. What we’re really seeing here are some hills and ridges on the edge of an asteroid, and the asteroid is about one, a little over one mile across. But what’s really interesting about this picture isn’t what it coincidentally looks like, but rather how it was taken. It was taken with a radar system, a very unique one on the Arecibo Telescope. Arecibo was an iconic radio telescope with a large dish a thousand feet across.  It was in Puerto Rico, and it conducted incredible scientific discoveries for 57 years.  Unfortunately, the telescope just this year suffered irreparable damage. It’s central receiver platform collapsed on December 1. The loss to the scientific community is significant. Arecibo was an active telescope. It was used to investigate brand new phenomenon like Fast Radio Bursts. It had a Nobel prize winning discovery to its name of binary pulsars made in the 70s. It was also used to confirm the first exoplanet that was found in 1992. Arecibo was also used to characterize asteroids. It had the most powerful planetary radar system in the world. So a planetary radar system is kind of different than how a typical telescope works. A telescope usually just passively collects light that’s already reflecting off or coming from objects in space, but a planetary radar system is going to beam out radio waves and then wait for them to reflect off an object, wait for the signal to return. And in studying differences in the waves sent out and the returned signal, we can essentially take a photo of the object that gives us a lot of information about it. And that’s how this picture was taken of this asteroid, and it can tell us things like the distance to the asteroid, the size and the shape. It can even show us the rotation. Let’s take a look at the rotation of this asteroid from photographs actually collected by Arecibo, and this was in April of this year. So there we see the asteroid as it was spinning. It spins once every four hours. And being able to figure out how asteroids rotate and also fine details of their orbits, how they move through space, that was the specialty of Arecibo. A lot of times we try to look for near-Earth asteroids, basically from using small telescopes to survey the sky. We want to look for things that could pose a threat to hitting us here on Earth, but once we find an asteroid, it’s hard to keep track of it to know where it will be in the future. Asteroids are a little different from planets because they are very small so their orbits change course a lot more easily from interactions in space. And being to at details in their motions and their size and their rotation, helps us track them a lot better. Arecibo was able to extend our knowledge of where asteroids would be, sometimes taking us from only knowing where they are for a few years, to knowing where they’re likely to be for centuries. This asteroid, it was able to tell for the next 100 years that it’s not a threat to Earth, that it’s not going to collide with us. In April it came within 16 times the Earth-Moon distance, and it’s next close approach will be in 2079 when this asteroid is four times the Earth-Moon distance. With Arecibo no longer able to function, we’ve had a great loss of being able to understand the asteroids that are nearby our Earth.

UNG Planetarium

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