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Got Milk?
The Galaxy >
This week is a perfect week to go outside in the later evening and have a Milky Way. Few laymen really have a grasp of what that famous big band of starry light is and our place in it. Let's investigate.
First imagine a disk, very thin compared to its breadth, like a CD. The galaxy we live in is like this; but a thin disk over 100 thousand light years across made up of over 100 billion stars.
There are actually stars all over the disk, but it's called a spiral galaxy because the bigger, brighter, show-off stars are located in what are called spiral arms, in effect lighting the arms up. A distant observer would see our galaxy as something resembling a flattened pinwheel of countless tiny lights. Our sun is nestled inside that disk, about two-thirds of the way out.
Now move your imaginative self into that disk. Looking around you see that the giant spiral now appears as a flat plane of stars surrounding you. It is this line of light that most of us know as the Milky Way, that band of stars painted over our heads during the summer nights.
But what about the stars which are not in the Great Band? Those stars all around us, even those nowhere near the band of light, are part of our Milky Way, too.
Our sun, Polaris, the stars of the Big Dipper and Orion are all part of the Galaxy. These thousands of visible stars are just close neighbors, above and below our position in the enormous spiral.
Bottom line? Everything you can see with your naked eye is part of our Galaxy, the Milky Way.
Then if there are over 100 billion stars why can we only see 1000's of them? You're sitting on the answer. The very stuff of you and the chair and your dog and the Earth is spread out all over the disk as fine microscopic dust. We live in a filthy galaxy. You can get glimpses of this dust as you look out at the Milky Way from a very dark place on a clear, Moonless night. Here's how.
Slowly moving your eyes from north to south along the Milky Way you'll notice discontinuities in the band of light. These dark blotches are the especially dusty areas in the disk.
But this crud is a good and wonderful part of the make-up of our special galaxy. That dust, created in stars and scattered about over the eons, can be used to make planets and dogs and you.
One recent insight into our position in the Milky Way is worth noting.
Our sun moves around the galaxy like a planet around a star. The whole grand tour lasts over 200 million years and takes our solar system in and out of the great spiral arms. At the moment we are off a spiral arm, which is actually a great place to be. Why?
Being inside a spiral arm it's dusty, and it would be hard to enjoy the entire rest of the universe. Imagine all the great telescopes, from Palomar to the Kecks to Hubble, trying to observe the great mysteries of creation from inside a dusty arm. Not a pretty thought.
Being off an arm opens up the skies like coming out of a fog. From our present position we can see millions of other galaxies and supernovae and gamma ray bursters and so on and so on.
One of the great "coincidences of life" puts us in the perfect seat at the perfect time for using the best instruments to study the magnificent wonders of the universe.
Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.
Posted by Administrator at 2003.07.19 01:20 PM | Comments (0)
