Our Galactic Home
Looking out into the Universe through the window of a clear night sky warmly bundled up with a warm drink on a cold, winter night is a great way to spend an evening. Since we live in a rural area where much of the land is forested, we can see lots of stars and other celestial objects. Now imagine you lived in a big city with skyscapers. Usually, you can only see the moon and a few of the brightest stars in the sky, because there are so many lights from Earth shining into the sky.
In New York City in 2003 and in Los Angeles in 1994 there were two enormous power failures or blackouts. When evening came, people in the city were able to see all the stars we can see at night, probably more. When they looked into the dark sky, they saw a “giant silvery cloud” running right across the middle of it. Some of them became scared. Many called 911 and local planetariums to report what they were seeing. What it a UFO or the end of the world? It was a mystery to them.
Do you have any idea of what that “giant silvery cloud” was?
That’s right. It was part of our own galaxy, the Milky Way. They were seeing billions of stars they had never known existed and it scared them.
The Milky Way Galaxy is our galactic neighborhood, part of our universal address, so let me tell you a little more about it. It is a spiral galaxy shaped like a pinwheel. Because of the spiral shape, we can see an arm of the Milky Way from Earth. To find this arm, we must look directly overhead for a blurry, cloudy, milky-looking band of stars. The reason this band looks so milky is because there are so many stars in it.
It is estimated at 200 BILLION stars! Our sun is just one of those stars. It is really hard for most people to understand what the number 200 billion means, so we will consider a model. If you were to pour bb's into a tin can at a constant rate, with each bb representing a star, it would take 32 years to listen to all the stars in the Milky Way. Now, that's a lot of stars! All these stars are not right on top of one another in our galaxy like it seems. They fill up a 3-dimensional space like all the things around us. The stars just look like they are 2-dimensional from our perspective on earth. As you look up into the Milky Way arm, you may notice that some stars appear to be much brighter than others. They may actually be brighter or they could be closer to earth or bigger than the others stars around them. The most brilliant stars are usually part of the most well-known constellations.
Almost everything we can see in the night sky is part of the Milky Way Galaxy with one exception. The furthest celestial object we can see, so far away it looks like a blur, is the Andromeda Galaxy. But we can talk about that galaxy another time.