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The Home Galaxy. What does the galaxy in which we live look like? via Cheryl's Mewsings
posted by thatwhichfalls (17 comments total)
Cheryl's Mewsings
posted by thatwhichfalls at 11:02 AM on August 16, 2005

This just in.
posted by gwint at 11:17 AM on August 16, 2005

Er.. Yeah, it's an interesting idea for a FPP, but maybe some other links would help. Like when the Milky Way grew a new arm, or the possibility of a weird ring of stars around the galaxy.
posted by Plutor at 11:18 AM on August 16, 2005

Shit, gwint, I knew I was forgetting something vital.
posted by Plutor at 11:18 AM on August 16, 2005

Here are some actual "plans" based upon astronomical observations.

The field of Galactic Cartography concerns itself with devising such 3-d models of our own galaxy but its tough going - there are a lot of uncertainties in the distances of what we see and much of the "other side" of the galaxy is hidden behind the galactic center and much of the rest of the disk.

Great *idea* for a post. Poor execution.
posted by vacapinta at 11:21 AM on August 16, 2005

My PhD supervisor makes 3-d scale models of the milky way etched into blocks of glass at a scale of around one to twenty-five thousand billion billion.

They're pretty cool.
posted by astro38 at 11:35 AM on August 16, 2005

"If our Milky Way were to resemble this one, we certainly would be proud of our home!"

heh heh.
posted by OmieWise at 12:32 PM on August 16, 2005

It is almost certain that we will never be able to send a probe out of our Milky Way to take a snapshot

Silly thing to say.
posted by Pretty_Generic at 1:05 PM on August 16, 2005

posted by alumshubby at 1:06 PM on August 16, 2005

What I've wondered for a while is what the night sky would look like if the Earth was very close to the center of the galaxy. Would it be nearly as bright as the moon?
posted by Citizen Premier at 1:37 PM on August 16, 2005

At arm's length, the nail on your index finger will cover the full moon.

The Hubble Ultra Deep Field image reveals 10,000 galaxies in an area 1/10th the diameter of the full moon (larger 349k image here.)
posted by cenoxo at 9:05 PM on August 16, 2005

Which makes me wonder, if, any particular direction you point, you run into a star, of galaxy gluster, why the night sky isn't bright, or at least have a brighter hue than BLACK, with a sprinkling of (close) stars.

How much is our atmosphere? even the Hubble photos show lots of black. I don't think light degrades...
posted by Balisong at 9:13 PM on August 16, 2005

Balisong, it spreads, though.
posted by Grod at 10:33 PM on August 16, 2005


Yours is a very old question known as Olber's paradox
posted by vacapinta at 10:36 PM on August 16, 2005


Re Olber's Paradox:

... if you move the Sun twice as far away from us, we will intercept one quarter as many photons, but the Sun will subtend one quarter of the angular area. So the areal intensity remains constant.

IIRC, the illumination of a subject is inversely square to its distance from the light source. If the Sun is twice as far away, the Earth will only get 1/4 of the Sun's original light. If the Sun is three times distant, the Earth only gets 1/9th the light, and so on, ad infinitum.

If the Sun or any other star is distant enough, their light falling upon the surface of the Earth would eventually be so weak as to be negligible, resulting in dark nighttime skies. Imagine a million flashlights spread across the surface of the Moon, pointed at the Earth: none of them would be individually bright enough to be seen.

What am I missing here? Aren't we getting luminance and illuminance confused?
posted by cenoxo at 11:41 PM on August 16, 2005

cenoxo: You're probably missing the fact that the expected number of stars at a given distance goes up as the square of the distance. The two effects cancel to give a constant brightness.
posted by edd at 3:54 AM on August 17, 2005

Olber's paradox is dumb. It's based on flawed assumptions. 1) Light sources are not uniformly distributed, they're clumped into galaxies, which are clumped into clusters and superclusters. 2) The observable universe is not infinite, thanks to the finite age of the universe and the equally-finite speed of light.
posted by Plutor at 7:10 AM on August 17, 2005

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