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enquiringman
2007-Jan-12, 08:44 AM
Guys, if the Milky Way is essentially a "flat" disk why can't I see a "band" of stars across the sky if looking towards it's centre?

Ken G
2007-Jan-12, 10:31 AM
You can-- looking in all directions along that disk, actually. That's why it's called the "Milky Way" in the first place-- it looks like a glowing white band. If you don't see it, try a darker sky in the country-- it's really quite obvious.

enquiringman
2007-Jan-12, 12:01 PM
Ken, thanks. I'm in Scotland. Which direction should I be looking?

01101001
2007-Jan-12, 02:04 PM
Ken, thanks. I'm in Scotland. Which direction should I be looking?

Up. Just kidding, but it's so big that if it's not washed out by local lights some of it will be up there.

So you know what you're looking for, try looking in topic Unaided-Eye Sight of the Milky Way (http://www.bautforum.com/showthread.php?t=43897)

(Some image links have gone stale. A quick pick of one: http://www.seqas.org/Images/milkyWay.jpg)

By the Way, nowadays, the Milky Way isn't the Universe, just a minuscule part of it.

enquiringman
2007-Jan-12, 02:30 PM
01101001, binary code for a digit, letter or other? Anyhow, thanks for the reply I'll check out the links. Ref the universe, I was wondering if the reason I couldn't see the "band" was that to the naked eye we could only see a sphere within our own galaxy and that's why it looked uniform. Didn't want to postulate that in my question - for obvious reasons!

Amber Robot
2007-Jan-12, 05:10 PM
Ken, thanks. I'm in Scotland. Which direction should I be looking?

Unless you are in an extremely dark spot, you might actually mistake it for a cloud. I remember the very first time I saw it I thought it was a cloud until I realized it stretched from horizon to horizon and was cutting straight the constellation of Cygnus.

You have to realize that even though the Galaxy is a flat disk and you have that band of stars across the sky, the Galaxy also has a lot of dust clouds that obscure a lot of those stars. Also, the Galaxy is much brighter in the direction of the Galactic Center than in the other direction, so those in the Southern Hemisphere tend to have a better view of the Milky Way. It's really quite impressive how bright the Galactic Center is as seen by the naked eye.

BISMARCK
2007-Jan-12, 05:10 PM
Yeah, if you get out to a really rural place on a really dark, clear, moonless night, the Milky Way will jump out at you.

I like looking at it when I go on vacation to the beach, if the sky is clear enough.

Ken G
2007-Jan-12, 05:39 PM
It's really quite impressive how bright the Galactic Center is as seen by the naked eye.

As I understand it, this is pretty much coincidence though-- you're not really seeing the galactic center (though it does indeed look impressive). Dust clouds obscure our vision of pretty much everything except the nearest spiral arm. So the "Milky Way" is really not a galaxy we are seeing, it is just a spiral arm of that galaxy, although in some directions you may be seeing other parts. Ironically, we see farther when we look away from those dust clouds along the disk, so it is actually other galaxies that give us a more complete visual look at what galaxies are like (in a telescope of course).

BISMARCK
2007-Jan-12, 05:41 PM
In a really dark, clear area, how easy is it to see Andromeda with the naked eye? I don't even know where to look for it.

Ken G
2007-Jan-12, 06:19 PM
It's near the square of Pegasus, barely but easily visible in a pretty dark sky.

BISMARCK
2007-Jan-12, 06:21 PM
Hmm. I need to get a map of the constellations and some binoculars for the next time I go camping or something.

Amber Robot
2007-Jan-12, 06:26 PM
As I understand it, this is pretty much coincidence though-- you're not really seeing the galactic center (though it does indeed look impressive). Dust clouds obscure our vision of pretty much everything except the nearest spiral arm.

No, I don't think it is a coincidence. I think you can actually see the central bulge.

See the following for example:

http://www.astropix.com/IMAGES/D_SUM_S/MILKYWAY.JPG

Or, check out this nice panorama (http://www.southernskyphoto.com/milky_way/images/milky_way_panorama_3.jpg)

BISMARCK
2007-Jan-12, 06:39 PM
Both of those pages are blocked, at least for me.

Sam5
2007-Jan-12, 07:00 PM
No, I don't think it is a coincidence. I think you can actually see the central bulge.

See the following for example:

http://www.astropix.com/IMAGES/D_SUM_S/MILKYWAY.JPG

Or, check out this nice panorama (http://www.southernskyphoto.com/milky_way/images/milky_way_panorama_3.jpg)

I couldnít get your link to work, but here is another one:

http://www.southernskyphoto.com/milky_way/central_milky_way.htm

Iíve read in a couple of books that what we see of the Milky Way with just our eyes is only areas that are maybe 3,000 or so light years away. The center is about 30,000 light years away. The direction toward the center from our viewing position tends to have more nearby stars in it than the direction away from the center, from our point of view. When it really looks like we are seeing the real center bulge is in radio and other electronic type photographs. The electronic cameras tend to be able to see through some of the dark dust clouds.

Sam5
2007-Jan-12, 07:01 PM
Both of those pages are blocked, at least for me.

Try this one from the same website....

http://www.southernskyphoto.com/milky_way/central_milky_way.htm

BISMARCK
2007-Jan-12, 07:02 PM
Thanks

Amber Robot
2007-Jan-12, 07:27 PM
Iíve read in a couple of books that what we see of the Milky Way with just our eyes is only areas that are maybe 3,000 or so light years away. The center is about 30,000 light years away. The direction toward the center from our viewing position tends to have more nearby stars in it than the direction away from the center, from our point of view.

Ok. Fair enough. But it definitely is brighter down there. And very impressive from a dark site.

Ken G
2007-Jan-12, 07:56 PM
Ok. Fair enough. But it definitely is brighter down there. And very impressive from a dark site.

I will admit that Sam5's lovely picture (thanks) does look a lot like a central bulge, and you can also see the dust absorption that conceals the center. It seems possible that most of what you see is nearby, but perhaps you can catch a glimpse of the bulge, making it all the more impressive. I don't know at the moment!

Sam5
2007-Jan-12, 08:00 PM
I will admit that Sam5's lovely picture (thanks) does look a lot like a central bulge, and you can also see the dust absorption that conceals the center. It seems possible that most of what you see is nearby, but perhaps you can catch a glimpse of the bulge, making it all the more impressive. I don't know at the moment!

Well, go to Google and look it up!

Lol, all I remember reading in a couple of old astronomy books is that we can't see any further than a few thousand light years, something like 3,000 to 4,000, because the dust and the stars themselves get in the way. Like not being able to see the center of the forest becuase our view is blocked by all the nearby trees.

But over the years I've seen better pictures of the "bulge" which were photographed with electronic cameras using radio waves, maybe x-rays, I don't remember.

Sam5
2007-Jan-12, 08:06 PM
Infrared photo:

http://www.seds.org/messier/more/mw_cobe.html

Sam5
2007-Jan-12, 08:08 PM
X-Ray:

http://chandra.harvard.edu/photo/2000/0204/index.html

Ken G
2007-Jan-12, 08:09 PM
Yes, it is certainly true that in infrared, radio, and X-rays, we can see the central regions quite well. Visible light can't get through dust, and ultraviolet has an even worse problem with hydrogen gas. But it's still conceivable you might get a visible glimpse of the bulge if it sticks up beyond the dust, which is kind of like what the visible picture looks like.

Amber Robot
2007-Jan-12, 08:10 PM
Well, go to Google and look it up!

I tried..


Lol, all I remember reading in a couple of old astronomy books is that we can't see any further than a few thousand light years, something like 3,000 to 4,000, because the dust and the stars themselves get in the way. Like not being able to see the center of the forest becuase our view is blocked by all the nearby trees.

Well, I don't think the stars are getting in the way. Certainly the dust can. And we can see other galaxies with the naked eye, so certainly the Milky Way has high enough surface brightness to be seen from Earth barring any obscuring dust.


But over the years I've seen better pictures of the "bulge" which were photographed with electronic cameras using radio waves, maybe x-rays, I don't remember.

Yes, Infrared images have been taken of the bulge. And they represent part of the evidence that the Milky Way is actually a barred galaxy.

Jeff Root
2007-Jan-12, 09:02 PM
I wanted to compare two of the images linked, one by 01101001
and one by Sam5:

http://www.seqas.org/Images/milkyWay.jpg
http://www.southernskyphoto.com/milky_way/central_milky_way.htm

I made all changes to the second image, which is smaller.

I flipped it both vertically and horizontally.
Then I rotated it left 30 degrees, which turned out to be almost
exactly the right amount of rotation.
I then cropped the edges off to leave an 800-pixel square.
Then I enlarged it to 900 pixels square, which again turned out
to be almost exactly the right amount of enlargement.

By aligning the images and jumping back and forth between them,
lots of differences and similarities can be seen, although they
are just differences in the pointing direction, optics, and
light-sensitive material, not in the sky itself.

-- Jeff, in Minneapolis

Ken G
2007-Jan-12, 09:35 PM
Can you tell if that is really the bulge that is visible? It sounds like you are confirming that it is.

Nereid
2007-Jan-13, 06:21 PM
The bulge is certainly visible in the 2MASS data (sorry, I don't have an easy ability to find and then link sites just now).

In any case, the MW that our eyes see is starlight (with some emission nebulae), integrated over the 'eye pixel' and the full line of sight. Above the plane, the dust absorption is considerably reduced, hence the effective depth of the line of sight is much greater, so the bulge (plus stars etc somewhat above and below the plane) shines through.

IIRC, there are also some 'holes' in our local arm, where the dust is thinner, and lines of sight are consequently deeper ... these appear to us as some of the brighter patches in the MW (of course, some bright patches are just relatively local star clusters, etc). The reverse is also true - the coalsack (visible to southern hemisphere folk) is a local dust cloud which blocks the milky light of the more distant parts of the MW ...

But you really do need a nice dark site, on a moonless night, to appreciate the intricacies (and brightness) of the tianhe/yinghe (heavenly/silver river).