How did we on earth find out what kind of galaxy the milky way is?

Question

I know they can classify galaxy spiral/elliptical ect.. But how did we know our own galaxy was a spiral. I would take millions of years for a telescope to photograph it from outside our galaxy. How did astronomers figure this out?

Answer 1

*laughing*

You don't have to send a telescope outside our galaxy!

The same way you know that the room you're in has the shape of a box by looking at the walls and judging the distances.

We measured the distances to other stars form the Earth and judged the shape.

Answer 2

You can map the sky in three dimensions if you can figure out how far stars are away from you.  Knowing the angle on the sky is easy enough to measure.

To get the distance, you use geometry to learn the distances to a whole bunch of nearby stars.  You learns lots about each one with spectroscopy, especially bright ones.  You learn their intrinsic brightness, so when you see a star that has the same spectrum, but is dimmer, you can work out how far away it is.  You then map tons of stars and build a 3 dimensional map.  The more stars you map, the better your map.

But lots of stars are hidden by gas and dust in the Milky Way.  So you have to go to radio or infrared wavelengths to see through it.  Both have been done.  The first paper suggesting that the Milky Way has a bar was done with radio.  Most recently, and infrared survey has produced a pretty good map of the galaxy.  But expect that the picture will change a bit, at least in detail, as time goes on.

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There is no longer any debate that the Milky Way is a barred spiral.  There's plenty of independent evidence of a bar.

Answer 3

It wasn't easy to find out, and we can't determine exactly how our galaxy looks. As someone else mentioned, the Milky Way is believed to be a barred spiral, although this is far from settled.

However, I can see for myself that the Milky way is a roughly flat, disc shaped galaxy. We see its arms stretch across the sky. There are fewer stars above or below the plain of the disc. In an elliptical galaxy, there would be an even distribution of stars across the sky.

Furthermore, by looking at other galaxies, we can infer how our own galaxy must appear. We see galaxies at all manner of angles, so it's kind of like looking at a series of photographs depicting a single galaxy at different angles.

There's a lot more to it than that, but if you have a look at other galaxies it becomes quite clear that we also live in a spiral.

Answer 4

its funny as i think they still debate as to whether its a spiral or a barred spiral.

but yes, the answerers above have explained it simply.

Answer 5

The Milky Way has been known since the ancients but was literally thought be milk from the breast of a goddess.

Since the invention of the telescope we have known that this faint light is made of billions of stars. It did not take long before the new astronomy of the 16th Century mapped out this faint light, and by 19th century spiral galaxies were spotted, as telescopes improved and became quite large instruments.

Lord Ross and Sir William Herschel played a large part in this

Successive improvements were made in telescope design such that Edwin Hubble in 1926 started the classification of these galaxies into 3 broad groups, Spirals, Barred Spirals and Elliptical (other categories were added later).

It was a combination of all these factors which led to the accurate plotting of our own galaxy which clearly shows the spiral arms (although astronomers disagree about how many arms it has).

So its nothing to do with how long it takes to photograph it, but how long it took for man to decipher its visible nature and what it meant.