Astronomy question

[Ankh-Morpork Guard]

Alright, this is probably something very simple but I've never been able to get a straight answer about it.

I've always seen maps and diagrams of our galaxy with the little 'You Are Here' or something similar to indicate where out solar system is. Well...how do we know our position in the Milky Way galaxy? To me, it almost seems like standing in the middle of Asia with a pair of binoculars and making a map without being able to actually see anything.

Anyone care to field this one?

 

[tarchon]

Measure distances to other stars. Plot the results in 3D. There you go. A lot can be inferred just from the apparent angular distribution, even without distances.

 

[jonesy]

Of course the map won't be all that accurate because of all the variables and distortions, but at those distances it doesn't really matter that much. A thousand klicks here or there is meaningless.

 

[Umbran]

Tarchon basically has it right.

You can, of course, get angular positions of the stars with a properly equipped telescope. The onl;y real question is how far away they are.

There are a couple of ways to figure that piece of information out. The basic one runs thusly - look at the color of the star. That tells you how hot it is. For the vast majority of stars, that also tells you how large they are - the size determines the rate of fusion, which determines the temperature. If you know these, you can then figure out how much light the star is really putting out.

Then, compare how much light you expect it to be putting out to how bright it seems to your instruments (it looks dim because it is far away). That gives you an estimate fo how far away it is from Earth.

 

[Storminator]

http://instruct1.cit.cornell.edu/courses/astro101/lec14.htm

 

[trancejeremy]

Bear in mind, there are lots of atronomy students and such that literally do this (calculate star data) all over the world, and have done this for probably a hundred years. There are a number of "Star Catalogs" which are essentially just great big lists of stars and their relevent stats, where they are, etc. So we actually know where a lot of stars are.

A great site on star mapping is at

http://www.projectrho.com/starmapstub.html

(Aimed at RPGs, too)

That said, I think most of the posters like that you see actualy use a photo of another spiral galaxy (Andromeda, usually).

 

[Terath Ninir]

That said, I think most of the posters like that you see actualy use a photo of another spiral galaxy (Andromeda, usually).

Pretty much, although they may take what we know about the Milky Way and extrapolate it. We don't know anything about the "back" of our galaxy -- the stuff on the other side of the core -- but spiral galaxies are pretty standard beasts. We know roughly where we are within our spiral arm, so one spiral is more-or-less as good as any other.

 

[tarchon]

There was an extra arm discovered just a few years back (http://www.cnn.com/2003/TECH/space/12/16/milkyway.boundary.reut/), so as the map coverage gets better, we'll probably see more new structure.

 

[Qlippoth]

There are a couple of ways to figure that piece of information out. The basic one runs thusly - look at the color of the star. That tells you how hot it is. For the vast majority of stars, that also tells you how large they are - the size determines the rate of fusion, which determines the temperature. If you know these, you can then figure out how much light the star is really putting out.

Apologies to Eric's Grandmother