Stargazing (Part 2) Ursa Major & Pinwheel Galaxy
The Fresh Perspective Podcast - Episode 20
How’s it going everyone? I’m Nick and you are listening to the Fresh Perspective Podcast.
If you haven’t yet listened to part 1 in this series, then what are you waiting for? It gives some great advice on how to plan and prepare for a good night of stargazing:
If you are up to speed, then it’s time to jump into part 2! To get the most out of this episode, download it onto your phone, step outside, hold your phone up to your ear, and follow along as we find and learn about the Big Dipper, the Big Bear (Ursa Major), Bode’s Galaxy, and the Pinwheel Galaxy. If you are listening indoors, then I hope you enjoy this dive into mythology and astronomy.
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I hope you did your homework from the last episode because it is time for a pop quiz! Go ahead and locate the Big Dipper.
If you are having a hard time, face north. It may be a little to the northeast or northwest, or it may even seem like it is straight above you. It’s a pretty large, bright, and popular group of stars, so if you haven’t found it yet, someone else in your party probably has. Four stars make the bowel, and it looks like three stars make the curved handle. Americans on the frontier looked at this group of stars and saw a drinking gourd, large spoon, or ladle. They saw something with which you would serve up water, or a hearty stew after a long day of pioneering, homesteading, trapping beavers, or whatever they did in those days. When Europeans see these stars, they see Odin’s wagon, a butcher’s cleaver, an old medieval plough, and a number of other things. Some Native Americans saw the bowl as a bear, chased by three hunters. In autumn, these hunters injure the bear, whose blood turns the leaves red.
In classical mythology, this bear wasn’t a bear at all, but actually the beautiful nymph Callisto, a follower of Artemis (the goddess of wild animals, the moon, and virginity). Zeus decided that Callisto would be his next mistress, but knew that she was sworn to a life of celibacy. To get around this, Zeus transformed himself into a woman who looked exactly like Artemis. They had a romantic encounter. Later Callisto was pregnant and gave birth to a son, which must have confused her and infuriated Zeus’ wife, Hera. Hera was so angry, that she turned this beauty into a bear. Years later, as Callisto was living in the woods, her own son, Arcus, found her! But he didn’t recognize her. He was a great hunter and chased her until she could run no further. Just as he was about to spear her with his javelin, Zeus intervened and spirited her up, into the sky. That is how Callisto became the constellation of the great bear. Her son was also transformed into a bear and became the constellation Ursa Minor, the small bear, or the “little dipper,” a constellation we will cover in the next part of this series. In some versions of the story, the constellation of Boötes, the herdsmen, is actually the boy hunter, Arcus.
The asterism of the Big Dipper has different names all around the world, but it belongs to a larger official constellation known as “Ursa Major” or “the Big Bear.” The Big Dipper is the bear’s lower back and tail. There you will find its brightest stars. The other stars of this constellation are much dimmer. If you start from the base of the tail and connect the top star of the dipper’s bowl, and then continue to hit the next two stars in that line, then you find the eye and nose of the bear. It is a fairly skinny bear that looks like she hasn’t eaten in a while. Below her eye is where her front limbs begin. Can you find her front legs? It looks to me like she is digging. The bear’s back legs are much larger. Start with the bottom of the bowl of the dipper. The back star, closer to the tail, is the back hip. Ursa Major’s back legs are spread wide like she’s taking a stand to protect her cubs. Find the next star down just below the hip and slightly back toward the tail. This is the top of the back legs. The left leg follows the curve of the front legs, and the right leg is straight down from the hip.
Once you find the eye, nose, and limbs of the bear, this constellation gets pretty big! In fact, it is the third largest constellation in the sky. Ursa Major doesn’t just look like a bear, it behaves like one. In the spring and summer, she is high in the sky and active. But when fall and winter come along, she hibernates low, along the horizon.
The brightest star here is Alioth. You can find it by looking at the three stars of the tail. It is the first one, closest to the rump of the bear. When you look at Alioth, you are looking at a star that is 81 light years away. The second brightest star is Dubhe and is found at the top front of the bowl of the big dipper, in the middle of the bear’s back. Dubhe is an orange giant, 123 light years away. It has a tiny yellow-white main sequence star next to it and they orbit one another as a binary. In the belly of the bear is the star Merak, which is just a cool sounding name. The last star at the tip of the tail is Alkaid. Alkaid is one of the hottest burning stars you can see without a telescope. It is a blue star, about 100 light years away, and is six times larger than our sun.
Now take a look at the middle star of the tail, the one that makes a kink in the tail. If you have really sharp eyes, or if you take a look at it with binoculars, then you have probably noticed something odd going on there. This is the star Mizar, but if you look close enough, Mizar is actually two stars. The second star is Alcor. This is another binary star system, where two stars orbit a point in space between them, like two partners in a dance. Can you see them both?
As we continue our exploration of our first constellation, go ahead and get your binoculars out if you have them. Better yet, if you have a telescope, get that ready. A telescope would make these deep space objects much easier to find.
It is time to spot two of the galaxies hiding in the darkness around the great bear. The first subject of our search will be M81, Bode's Galaxy. To find Bode’s Galaxy, we need to zero in on two stars in the big dipper. Look at the bottom of the bowl of the dipper, to the back star closer to the handle. That star is “Phad” with a “Ph.” Now find the diagonal star from it, forming the upper front edge of the bowl. That is our friend Dubhe again, the orange giant. Now if you connect those two stars and follow the line they create, you will run into M81, one of the easiest galaxies to see. The distance from the big dipper to the galaxy is about the same as the distance between Phad and Dubhe. Double the length of that diagonal line, and you’ll find it, a bright smudge in the darkness.
Bode’s Galaxy is about 12 Million Light Years away. Compared to other galaxies, that isn’t that far, making it easier to see in comparison. It belongs to our “Local Group” so, in cosmological terms, it is just down the street from the Milky Way. It’s about half the size of our galaxy and has 250 billion stars, but the black hole in its center is 15 times larger than the black hole in the center of the Milky Way. Just like Ursa Major, it is easiest to see in the spring.
To wrap up this part of the sky, I have a challenge for you. In these episodes, I think it would be fun to see if you can find some of the more difficult objects to see. Your challenge tonight is to spot the Pinwheel Galaxy!
The Pinwheel Galaxy (M101) is one of the most popular spiral galaxies in our sky. Finding it can be pretty tricky at first, and will probably take you a few tries. Through your binoculars, it will be a blurry patch. Through your telescope, you will be able to spot its bright center.
Find the last two stars in the bear’s tail, Mizar and Alkaid. These form the two bottom corners of an equilateral triangle (or a triangle with all three of its sides being the same length). The top point of this triangle is invisible, but if you look with strong binoculars or a telescope, it appears. The Pinwheel Galaxy is just about where the tip of this imaginary triangle would be. You can think of it as a fly, pestering the tail of the great bear.
The Pinwheel Galaxy is about 20 million light years from Earth, and it hosts many young bright stars. It is asymmetrical. This is probably because it crashed into another galaxy and absorbed it in the distant past. It is 70% larger than our home galaxy, is found beyond our Local Group, but is still in our neighborhood. It is a member of the Virgo Supercluster, along with our Milky Way and the Andromeda Galaxy. For all of you who can find tonight’s challenge, be sure to let us know in the comments!
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That is all I have for you today, but the conversation continues across social media and in the comment sections below. Do you agree with today’s message? Am I mistaken about some detail? How can I better elaborate on this topic in the future? Feel free to share your perspective!
Written By Nicholas Burk, Executive Board Member © 2019 Free Thought Initiative