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Author Topic: How do we know what our galaxy looks like?  (Read 4276 times)

Eric A. Taylor

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How do we know what our galaxy looks like?
« on: 01/11/2009 13:51:37 »
No Earth based human has seen the Milky Way Galaxy from a distance. Drawings of the galaxy are lovely spirals with several arms and look a lot like the Andromeda Galaxy. Assuming that galaxy looks like our own is like assuming you look a lot like the person next to you if you've never seen your reflection. If I were sitting next to a person who is of African decent I'd be able to tell that my lips were thinner and my nose longer by carefully feeling my own face so I'd know I didn't look exactly like him but I'd never guess my own skin was a lot lighter than his.

  Is it possible we live in an irregular galaxy or maybe a disk galaxy that looks nothing like Andromida. Are there other galaxy that look like twins close together.

  Is it possible we could see a "reflection" of our galaxy because it's light has made a 1/2 orbit around a black hole returning to our eyes a few million years later.
« Last Edit: 04/11/2009 02:14:08 by mountaineirc1969 »

Mr. Scientist

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Re: How do we know what our galaxy looks like?
« Reply #1 on: 01/11/2009 15:28:58 »
We can observe a great deal of our galaxy, and with modern computers, able to map it out visually.

graham.d

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Re: How do we know what our galaxy looks like?
« Reply #2 on: 01/11/2009 16:31:11 »
We can measure (by various means, estimate) the distances and brightness of the stars in our galaxy and, more obviously, measure accurately the relative angular positions of each one. This gives a 3D map of our galaxy which can be easily manipulated to produce an image viewed from any position inside or outside the galaxy.

Vern

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Re: How do we know what our galaxy looks like?
« Reply #3 on: 01/11/2009 18:44:29 »
The University of California, San Diego Center for Astrophysics & Space Sciences has a nice web page about the shape of the Milky Way and how it is determined.


LeeE

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Re: How do we know what our galaxy looks like?
« Reply #4 on: 01/11/2009 20:02:59 »
Is it possible we could see a "reflection" of our galaxy because it's light has made a 1/2 orbit around a black hole returning to our eyes a few million years later.

Just to address one point that the others haven't yet; no, it is not possible.

For light to make a half-orbit around a Black Hole the orbital velocity at some point outside the Event Horizon would have to very nearly equal the speed of light 'c'.  If the light goes any faster than the orbital velocity it will escape orbit and when you work out the orbital radius for a Black Hole, where the orbital velocity equals 'c', it turns out that it is quite a long way inside the Event Horizon.  IIRC, the orbital velocity at the Event Horizon  is somewhere around 2/3rd 'c', but work it out for yourself to be sure.

Eric A. Taylor

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Re: How do we know what our galaxy looks like?
« Reply #5 on: 01/11/2009 22:12:27 »
Thanks for the black hole thing.

  Problem with mapping our galaxy's stars. We can't see most. Due to dust and gas in the disk of our galaxy we can only see a small part of it. Imagine trying to map London from one building on a very foggy day. Even in a tall building you won't see much of the city.

  For sure we don't even know how many stars are in our galaxy. I've heard numbers between 100 billion and 400 billion (thousand million) that's a difference of 400%!!!! Not a very good guess.

graham.d

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Re: How do we know what our galaxy looks like?
« Reply #6 on: 01/11/2009 23:08:34 »
Only 100% to 400% - that's a fairly small tolerance by astrophysics standards :-) We can still see much more detail in our galaxy than that in another galaxy though because the stars are very near by comparison. The galaxy may have dust but it is still fairly transparent. The gas and ion density is also very low, though enough to create a very small refractive index, which is used as one of the ways to measure distances (by virtue of the dispersion in time of the arrival of different wavelengths of the regular electromagnetic emissions from pulsars).

 

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