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Visibility of milkyway center.
Hi all,
Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. TIA peter |
#2
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Dear peter:
"peter" wrote in message ... Hi all, Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. When you live in a neighborhood with trees, it is not uncommon to not be able to see the tall buildings downtown, but you can see the Moon. In the Milky Way, there is a lot of dust along the plane of its ecliptic that scatters/absorbs light. David A. Smith |
#3
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In message qVXoe.3103$7s.1455@fed1read01, "N:dlzc D:aol T:com (dlzc)"
writes Dear peter: "peter" wrote in message u... Hi all, Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. When you live in a neighborhood with trees, it is not uncommon to not be able to see the tall buildings downtown, but you can see the Moon. In the Milky Way, there is a lot of dust along the plane of its ecliptic that scatters/absorbs light. Very minor nitpick - that's equator, not ecliptic :-) If you look at a picture of an edge-on galaxy you can't see the bright centre and the view is quite like the centre of our galaxy. Look at http://celestialwonders.com/ngc891_20040120.html, for instance. And in infrared you _can_ see the centre http://itss.raytheon.com/cafe/dirbe/f4b1p.html. -- Remove spam and invalid from address to reply. |
#4
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Dear Jonathan Silverlight:
"Jonathan Silverlight" wrote in message ... In message qVXoe.3103$7s.1455@fed1read01, "N:dlzc D:aol T:com (dlzc)" writes Dear peter: "peter" wrote in message . au... Hi all, Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. When you live in a neighborhood with trees, it is not uncommon to not be able to see the tall buildings downtown, but you can see the Moon. In the Milky Way, there is a lot of dust along the plane of its ecliptic that scatters/absorbs light. Very minor nitpick - that's equator, not ecliptic :-) "Those French. Its like they have a different word for *everything*!" Thanks for the correction. He hadn't had a response (apparently) for several hours, and so I attempted a reply. If you look at a picture of an edge-on galaxy you can't see the bright centre and the view is quite like the centre of our galaxy. Look at http://celestialwonders.com/ngc891_20040120.html, for instance. I was going to also add that in galaxies that we *can* see the center, the distance from us to center and us to edge are very close to the same value, so individual intensities of stars would be roughly the same. This wouldn't be true for observations within the Milky Way. Local stars would be much brighter (in general) than more distant stars. And in infrared you _can_ see the centre http://itss.raytheon.com/cafe/dirbe/f4b1p.html. Excellent, so the OP has a more complete answer! David A. Smith |
#5
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"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in message news:qVXoe.3103$7s.1455@fed1read01... Dear peter: "peter" wrote in message ... Hi all, Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. When you live in a neighborhood with trees, it is not uncommon to not be able to see the tall buildings downtown, but you can see the Moon. Are the stars in the middle of the galaxy too far away to see? (about 15k lightyear away?). I look at the milkyway and just can't understand how come the center is not bright. Thanks for your patience. In the Milky Way, there is a lot of dust along the plane of its ecliptic that scatters/absorbs light. Are you saying that somthing is between us and the center of the galaxy, that stops light from getting through? David A. Smith |
#6
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In message , peter
writes "N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in message news:qVXoe.3103$7s.1455@fed1read01... Dear peter: "peter" wrote in message ... Hi all, Please couls someone explain, (simple, simple terms please), how it is that the center of our galaxy is not visible in the night sky. I would have thought that that many stars in one place would light up the sky. When I see pics of other galaxies, they have a bright center. When you live in a neighborhood with trees, it is not uncommon to not be able to see the tall buildings downtown, but you can see the Moon. Are the stars in the middle of the galaxy too far away to see? (about 15k lightyear away?). I look at the milkyway and just can't understand how come the center is not bright. The individual stars certainly are. There are a few bright stars like Deneb in Cygnus which are bright though they are 3000 light years away, but that's about 10,000 x as bright as the sun and much closer. The next step is to actually do some work :-) and find out how bright the central bulge would be. My guess is that it wouldn't actually be very bright - photos give a misleading impression. Perhaps as bright as Venus, but spread over several square degrees - bigger than the Moon. In the Milky Way, there is a lot of dust along the plane of its ecliptic that scatters/absorbs light. Are you saying that somthing is between us and the center of the galaxy, that stops light from getting through? Yes - the same dust you see in the edge-on pictures of other galaxies. Mostly carbon, and about the same size as a wavelength of light. I can't find a figure for the number of particles in a given volume, though. |
#7
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In article ,
Jonathan Silverlight writes: The individual stars [in the Galactic center] certainly are [too far away to see] With naked eye, yes, although not be much. The bright red supergiant IRS 7 has a dereddened 2.2 micron magnitude of 4.0. If it is spectral class M0 (which is about right but I'm too lazy to look up the exact class right now), it would be about mag 8.0 in the visible if there were no reddening. (With reddening, it's around mag 35.) IRS 16 might be brighter, though I don't think anyone knows for sure what its intrinsic spectrum is. It has a dereddened 2.2 micron magnitude of 5.6 and is fairly blue. (reference: Becklin et al. 1978, ApJ 219, 121.) -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
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