Accurate distance of the milky way?

Question

How were we able to determine the size of the milky way? I heard that we have not sent any shuttles or probes that far out so how did we know how many arms it has, the size, and where we are located within the milky way?

I don't want to know how far it is. I'm asking how we came up with that information?

Answer 1

When we look at the Milky Way, it has definite structure even in visible light. It lies in a plane. A lot of other galaxies lie in planes like that, and they are all spiral galaxies, a very common shape for galaxies. So the first assumption made was, the Milky Way lies in a plane, therefore it is probably like other galaxies that lie in planes, therefore it is probably a spiral.

The second assumption was that it was probably like other spirals. We can determine the distance to the Andromeda Galaxy (M31), a spiral that is very close to us, using standard astronomical methods. And since we know how far away M31 is, we know how big it is too: it's about 100,000 light years in diameter. So the second assumption is that the Milky Way is a lot like M31.

The next thing we do is look at the distribution of globular clusters. Globular clusters are part of the galaxy, but unlike most parts, they don't necessarily lie in the galactic plane. By looking at all the globulars and finding their distances, we begin to get an idea of how large our galaxy is, and where the center might be. When we do this, it turns out that 100,000 light years seems about right, and the most likely direction for the center is in the constellation Scorpius.

Then we look at the galaxy in infrared light, and we see it has a definite bulge toward Scorpius, like other spiral galaxies seen edge-on. Here's a photo of the Milky Way in infrared:
http://www.phys.ualberta.ca/~pogosyan/teaching/ASTRO_322/images/milkyway_infrared.png

... and here's a photo of a spiral galaxy seen edge-on:
http://apod.nasa.gov/apod/ap040409.html

And finally, after doing very extensive surveys of the stars in the galaxy, including their distances, we are able to slowly map out the structure of the arms; and, it turns out, the Milky Way is of a type known as a "barred spiral" which is fairly rare.
http://images.google.com/imgres?imgurl=http://www.news.wisc.edu/newsphotos/images/Milky_Way_galaxy_sun05.jpg&imgrefurl=http://www.news.wisc.edu/newsphotos/milkyway.html&h=2700&w=2700&sz=1928&hl=en&start=1&um=1&tbnid=tw7sYR68MD927M:&tbnh=150&tbnw=150&prev=/images%3Fq%3Dmilky%2Bway%2Bgalaxy%26svnum%3D10%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DN

Here's another barred spiral:
http://www.noao.edu/outreach/aop/observers/m58mandels.jpg

Answer 2

We haven't even sent any probes outside our own solar system, nevermind 100,000 light years away.

We can tell by looking at stars through telescopes and measuring their distances. By doing this to thousands of stars, you can determine where they clump together to form structures like arms, and you can see where they drop off at the ends of the galaxy.

v v v It depends on your definition of "accurately", Sami. Considering the Universe is billions of light years across, if we can measure the diameter of the galaxy to within 10,000 light years, I'd say it's pretty accurate.

Answer 3

It is mainly done through radio astronomy, mapping areas of hydrogen in the Milky Way's spiral arms.

Answer 4

I think its 140,000 light years in size. They determined it by checking how fast the stars on the edge of the galaxy are moving away from/towards us. And because the universe is expanding a certain rate, they can use calculus to determine how far away those stars are.

Answer 5

its like this-pretend there were no mirrors on earth. you could not see yourself. but you could feel your face and feel like a bump and a hole and this coarse stuff on the top of your head. you would know by looking at OTHER people (in this case other galaxies) what you looked like. also, we can see towards the inside of our galaxy and using parallax can determine the distance of the furthest star in it

Answer 6

It may be 100,000 light years but the fact remains it is humanly impossible to measure the distance accurately!

Answer 7

Its estimated at 100,000 light Years.