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

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

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.

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

"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

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.

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
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