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Q and A on the Milky Way
The Galaxy >
Today's quiz is brought to you by our home galaxy, the Milky Way. Now remember that the occasional friendly quizzes that we take here are just a fun way of educating ourselves about the universe. No need for clammy hands and palpitating heart. Sit back and have fun.
True of false: The Milky Way always looks the same in the night sky.
The Milky Way has been seen known since humans have walked this earth. It is that glimmering stretch in the nighttime sky so dense with stars it looks like a river of milk.
It turns out it is just the disk of stars, the galaxy we live in, seen edge-on; our stellar spiral of brightness filled with well over 100 billion stars.
But it doesn't always look the same throughout the year. During the summer, when our nighttime sky faces the center and most star-filled part of the disk, the Milky Way is at its brightest and most beautiful.
But our orbit around the sun means that six months later, during winter, our nighttime sky faces away from the dense part of the spiral out towards the less populated suburbs. The Milky Way then is not easily seen.
And the way it moves between these two extremes is rather counterintuitive. If we could see how it changes week to week, it would look like a giant hoop sweeping overhead, like a cosmic jump rope.
This means that during Fall and Spring, between the two extremes, the Milky Way is in a position which makes it appear to surround us on the horizon, essentially invisible to us.
True or false: Until recently the Milky Way was all there was in the universe.
In days of old when one looked up on the giant collection of stars overhead, it was reasonable to believe that the multitude of stars was all there was, that we lived in a star system and there was nothing beyond it. There were barely perceptible spiral clouds, "faint fuzzies" as an astronomer friend of mine calls them, believed to be local clouds of gas and dust or planetary systems.
Then along comes a man named Edwin Hubble. He sees the same faint spiral clouds above but thinks they are very distant galaxies, vast collections of stars hundreds of billion strong. To prove it he needs to find a special star called a Cepheid variable, a star that has an intrinsic brightness that astronomers can use to determine its distance.
Thankfully, the new telescope on Mount Wilson had just been completed. Through those giant eyes he found some Cepheids in the Andromeda Nebula. He was right; Andromeda was an entire galaxy unto itself, not part of our own. In one single discovery, the size of the universe exploded.
It turns out now that universe is unimaginably bigger than out galaxy. The Milky Way is only about 100,000 light years across. The visible universe extends probably more than 14 billion light years in all directions.
True or false: We don't know what most of the Milky Way is made of.
You'd think that in a day and age where knowledge flows like the mighty Amazon, that we would at least know what the Milky Way is made of. Well, embarrassingly enough, we don't. Here's why.
We know how objects should move about. For example, the planets move around the sun in such predictable ways that we can land spacecraft on planets within meters of where we want.
So it was thought that the stars moving around the galaxy should move predictably as well. Oh, that they would!
The stars out in the suburbs of the galaxy should move very slowly, like distant Pluto does around our sun. But in fact, and to the surprise of astronomers, they don't. They move way too fast - that is, too fast if all there is to the galaxy is what we see.
There must be something that makes up a lot of our galaxy - perhaps 95% of our galaxy! - which is made of matter, but matter we cannot see - a sort of dark matter.
What is it? No one knows yet. Stay tuned. For now, though, this statement is true.
Hope you did well! Until next time, clear skies!
Posted by Mark Ritter at 2007.02. 4 05:42 PM | Comments (0)
