hi, I understand that the Milky Way galaxy is relatively flat due to the combined effects of gravity. Since this is the case, why does there appear to be a uniform distribution of stars in the night sky? I would expect a thick area in the direction heading towards or away from the center of the galaxy.
There is; that’s what the “Milky Way” that our galaxy is named after is, the collective light of many stars.
My uneducated guess would be that we can’t see far enough with the naked eye to see how heavily populated the sky is in some directions.
What you probably mean is why is there a uniform distribution of *nearby *stars, that is, stars that are close enough to be seen by the naked eye as distinct sparks in the night sky. That question answers itself: because you’re looking at very close stars, most only a few dozen to a few hundred light-years away. (The most distant star you can see with the naked eye under ordinary conditions is Deneb, about 1600 light-years away.) But the Milky Way is about 1000 ly thick, so all you are seeing with the naked eye at night is a tiny bubble of the closest stars in the Milky Way, a bubble that doesn’t really reach past the local thickness.
You can, of course, see the light from the massed stars of the Milky Way along the direction towards its center, but they no longer appear as individual sparks, but a broad strip of faint…well, milk.
If the OP has never spent time somewhere relatively dark, it’s possible he’s never seen the Milky Way. I grew up in Little Rock, a small city, and even though I went camping a few times as a kid, I don’t remember clearly seeing the Milky Way at night until I lived in Colorado as an adult.
Even if you do see the Milky Way, it is, as the name suggests, a faint, milky cloud of light, not a cluster of individually visible stars. If you look at the stars that can be distinguished individually in the night sky, they seem more-or-less evenly distributed to me.
ETA: Huh, ninjaed. With an answer.
I guess I don’t know my own galaxy well enough, too many darn lights around here!
It’s called “Light Pollution”. You need a clear, moonless night away from most civilization. I’ve only seen the Milky Way when I was stationed on San Salvador, Bahamas.
This. Kind of sad, in a way, since the Milky Way was prominent before artificial lights.
Earth isn’t the only planet where the grandeur of millions of stars is unseen:
[QUOTE=Nightfall, by Isaac Asimov]
Aton, somewhere, was crying, whimpering horribly like a terribly frightened child. 'Stars – all the Stars – we didn’t know at all. We didn’t know anything. We thought six stars in a universe is something the Stars didn’t notice is Darkness forever and ever and ever and the walls are breaking in and we didn’t know we couldn’t know and anything – ’
Someone clawed at the torch, and it fell and snuffed out. In the instant, the awful splendor of the indifferent Stars leaped nearer to them.
On the horizon outside the window, in the direction of Saro City, a crimson glow began growing, strengthening in brightness, that was not the glow of a sun.
The long night had come again.
[/QUOTE]
The word “galaxy” is itself derived from the Greek word for milk. “Milky” words like “lactation” go back to the same Indo-European root as “galaxy”.
Also, it’s winter in the Northern Hemisphere as of this post, but either way, looking in toward the galactic center where it’s a bit brighter (around Saggitarius) you’ll have to wait until summer to see.
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But, otherwise, I prefer the winter skies for observing (with a great set of binoculars). Overall, more interesting stuff.
And now that I’m outside the Memphis area, I’m benefiting from much less light pollution (and much warmer nights) than in the Detroit, MI area. The difference is amazing, really, almost worth the hassle of moving out of state for that alone.
Right, when you look towards the center of our galaxy, you see the Milky Way. What about looking outwards, away from the galactic center? Are the outer arms distinguishable as part of the galactic disc?
Here are some long exposure shots that may give you an idea of what you’d be seeing in very rural places away from city lights.
http://pic.uuhy.com/uploads/2011/08/03/025-long-exposure-photos.jpg
http://www.astro.wisc.edu/sirtf/skymt_payne_big.jpg
Enjoy!
Beautiful photos!
Some day, if you get a chance, go to Cloudcroft, NM. On a cold clear night, drive just outside of town in the direction of the observatory. Stop at the scenic overlook, get out of your car and look up. Try not to fall over backwards.
Wow, those cactuses are totally flipping off the universe.
Yes, that is the winter Milky Way (in the Northern Hemisphere, that is). The galactic center is in Sagittarius, and is the densest, brightest part of the summer Milky Way.
Use theDark Sky Finder map. If there is insufficient dark sky where you live, plan a summer road trip!
Like you said, those are long-exposure shots. Is the Milky Way ever that clear and bright to human eyes?
Almost certainly not to that extent, but in an area with not much light polution the Milky Way is pretty obvious.
I think it’s pretty cool that we can easily (well, those of us outside big cities) look along the plane of our galaxy.