MadSci Network: Astronomy Query:

### Re: How many stars in the milkyway galaxy?

Date: Wed Feb 10 10:21:01 1999
Posted By: Mike Francis, Other (pls. specify below), Physics/Astronomy, Self employed/ Amazing Discoveries Productions
Area of science: Astronomy
ID: 918517243.As
Message:

Dear Beatrice,

The exact number of stars in our Milky Way Galaxy is virtually impossable to determine, but best estimates put the number at over 100 billion stars. The reason its so hard to determine the number of stars is three fold. First the galaxy is so large we can't really use measurements in miles or kilometers, we use instead light years. The distance light travels in one year is one light year. The Milky Way is about 80,000 light years across. As we look towards the center of the Milky Way, in the direction of the constellation Sagitarius, we must look through millions of stars. Try looking into a crowd of people when you're part of the crowd. Now try to count how many people are there. It's quite a task.

Now lets add the vast quantities of interstellar dust that lie between the stars. Visual light can't pass through the millions and millions of miles of dust. We turn to radio astronomy, which uses the long wavelength radio waves from stellar activity. These radio waves aren't absorbed by the interstellar dust so we can use them to get a better picture of the size and structure of our galaxy. This picture is of a galaxy that looks somewhat like a giant pinwheel, rotating once about every 200 million years.

The final problem to take into account is that not all of the stars in our galaxy may put out enough visable or radio energy to be seen at all. What you can't see you can't count, so scientist must look at how the galaxy behaves and what the can see to estimate how many stars must be there to explain what they observe.

If you want to learn more about the Milky Way or about galaxies in general try http://map.gsfc.nasa.go v/html/milky_way.html.

Mike Francis

http://www.gis.net/~mtf/sm.htm

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