Expert: Ed - 6/30/2008

Question
QUESTION: How did they form the image of the milky way?

ANSWER: Hady,

I am not sure which image you are referring to.  Is this the one?

http://www.sciencedaily.com/releases/2007/12/071210112009.htm

Please get back to me, if you are thinking of something else.

Keep Looking Up!
-Ed

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QUESTION: No i mean the usual picture with the spiral arms.
how did they know that this is the shape of our galaxy and they couldn't have seen it

ANSWER: Hady,

There were several reasons.  For one thing, as astronomers study the stars in the Milky Way individually, they can detect certain general patterns of movement which correlate perfectly with what we can observe in other galaxies, which we can see are spiral in shape.

For another thing, in terms of comosition, we can see that the amount of gas in local interstellar nebulae, the color of that gas, and also the dust content of our galaxy are reminiscent of what we observe in galaxies which we know to be spiral.

Also, simply, when you look up at the Milky Way, it basically looks like a big whitish stripe across the sky.  It looks like a STRIPe.  Nobody calls it the Milky Egg, or the Milky Trapezoid, or the Milky Thing Up In The Sky That's Shaped Oddly Like Paris Hilton.  The fact that it looks like a stripe tells us that it must be some kind of flat, elongated shape seen from the side.  Spiral galaxies are shaped like this.

Here is a lecture from Ohio State, which discuesses the history of our attempts to understand the Milky Way.  It gives you a few people's names to google!
http://www.astronomy.ohio-state.edu/~ryden/ast162_7/alternate28.html

This link is more thorough:
http://www.gb.nrao.edu/~glangsto/lessons/lessonHISTORY.html

Please let me know if you would like more detail,, but I think this is basically what you are looking for.

Keep Looking Up!
--Ed

---------- FOLLOW-UP ----------

QUESTION: I asked this before but how can we see the galaxy as a stripe although we live on it,it's hard to imagine .and how did they know the number of spiral arms of our galaxy and how did they know where do we exist in the galaxy?
Thanks

Answer
Hady,

This recent article from the Spitzer space Telescope folks has a lot of information for you.
http://www.spitzer.caltech.edu/Media/releases/ssc2008-10/release.shtml

This too:
http://homepage.mac.com/astronomyteacher/documents/globular.pdf

Also, remember that the Milky Way is thickest, and brightest, in the direction of the constellation Sagittarius.  In that general direction, and for a few constellations in either direction away from it, the Milky Way looks most like a stripe.  That's because, in THAT direction, we are facing toward the middle of the disc that is our galaxy.  In other directions, the Milky Way is fainter, because then we are looking out away from the center of our galaxy.  Stars are fewer, and farther between, out there.

An astronomer named William Morgan made major contributions to this field of study.  I just want to give him some credit here.
http://chronicle.uchicago.edu/940714/morgan.shtml

I'm sorry, I need to go outside right now to circulate a petition against global warming.  I'm supposed to meet some people.  If you want to get back to me again, that is fine.  I will have more time later.

Keep Looking Up!
--Ed