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The_Radiation_Specialist
2005-Dec-22, 12:30 PM
This question appeared in my mind when I looked at sky last night:
If we can clearly see stars such as Sirius and Rigel from earth with unaided eye, Then why cant wee see the very bright centre of Milky way? Shouldnt there be a very bright clound of stars(center of milky way) visible from earth every night?

ryanmercer
2005-Dec-22, 12:42 PM
That is a good question.

PhantomWolf
2005-Dec-22, 01:15 PM
The major reasons are that the galaxy we are in is a disc shape (well a disc with arms) and we're in it. That means we see it as a line. If you look at the dark night sky (you need to have few lights nearby) you'll see the ribbon of the Milky Way any night that is clear and dark, so in a way you can see it. Of cause the actual center is quite a way from us due to our position out in one of the arms and depending on the time of year the sun is between us and it. It's not really totally obvious to the naked eye however as there is a lot of dust and gas between it and us and so it is just like the rest of the ribbn of the Milky Way. Astronomers generally can find it though. ;)

tofu
2005-Dec-22, 01:16 PM
In fact, we can see most of the Milkyway, and let me tell you, it is a beautiful and amazing sight! The last time I was able to see it was in 2004, after hurrican Ivan hit and knocked out the power for miles and miles around. You can also see the Andromeda galaxy with the naked eye.

Unfortunately, with the street lights back on, all you can see are the really bright stars. It's sad.

At any rate, as you might expect, if there are more stars in the center of the galaxy, then there is more stuff to make stars at the center of the galaxy. In other words, more dust to obscure stars. So that's the reason it's dim, but I assure you, it's there. I've seen it.

Jason Thompson
2005-Dec-22, 01:18 PM
The centre of the galaxy is visible from somewhere on Earth every night. If memory serves it lies in the constellation of saggitarius as seen from Earth, though I am open to correction on that point. Where and when it is visble is determined by the rotation of the Earth, the tilt of the Earth's axis relative to the plane of the solar system, and the angle of the solar system relative to the galactic plane.

However, it is not so bright because a) it is considerably further away than the other stars in the sky, and b) there is also a large amount of dust in the galaxy, which tends to obscure more distant objects. There is a large dust lane between us and the galactic centre.

If you travel to a more favourable location for observing, such as one where the centre of the galaxy is favourably placed at a sensible hour (generally more equatorial lattitudes I believe), and where there are no sources of light pollution for some distance, you will see the galactic centre.

ngc3314
2005-Dec-22, 01:35 PM
This question appeared in my mind when I looked at sky last night:
If we can clearly see stars such as Sirius and Rigel from earth with unaided eye, Then why cant wee see the very bright centre of Milky way? Shouldnt there be a very bright clound of stars(center of milky way) visible from earth every night?

You just need different eyes - in the infrared, radio, and X-ray bands, it's very prominent. But for optical astronomy, there is a downside to living out in the disk of a spiral galaxy. There are several spiral arms' worth of dust-laden interstellar matter between here and the center. Pack that much stuff between here and the Sun and you'd need binoculars to pick it out. As one poster already said, we can see enough of the surrounding stars in the central bulge to make the Sagittarius Milky Way something special even to the naked eye.

Hamlet
2005-Dec-22, 05:03 PM
This question appeared in my mind when I looked at sky last night:
If we can clearly see stars such as Sirius and Rigel from earth with unaided eye, Then why cant wee see the very bright centre of Milky way? Shouldnt there be a very bright clound of stars(center of milky way) visible from earth every night?

A lot of visible light coming from the galactic center is obscured by dust. However, by looking at the right wavelengths we can see into the center of the galaxy. The Spitzer Space Telescope (http://www.spitzer.caltech.edu/), which operates in the infrared, has started to provide some very interesting glimpses into the heart of the Milky Way (http://www.nasa.gov/vision/universe/starsgalaxies/spitzerf-20051213.html).

Tim Thompson
2005-Dec-22, 09:03 PM
Indeed, we cannot see the center of the Milky Way in eyeball, visible light, because it is enshrouded in thick clouds of dust. However, the center of the Milky Way is visible in wavelengths that penetrate the dust.


UCLA Galactic Center Group (http://www.astro.ucla.edu/~jlu/gc/index.shtml); they can see the stars orbiting the supermassive black hole at the center of the Galaxy, and derive its mass by orbital mechanics.
X-Ray Mosaic Of Galactic Center (http://chandra.harvard.edu/photo/2002/gcenter/); the CHANDRA X-ray telescope can see the X-ray emission from hot material surrounding the central black hole.
Spitzer Exposes Our Galaxy's Deepest Secrets (http://www.nasa.gov/vision/universe/starsgalaxies/spitzerf-20051213.html); the infrared Spitzer Space Telescope can see star clusters hidden behind the dust that shrouds the galactic center region.
A size of ~1AU for the radio source Sgr A* at the centre of the Milky Way (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Natur.438...62S&db_key=AST&d ata_type=HTML&format=&high=4366fa465119620); Zhi-Qiang Shen, et al., Nature 438(7064): 62-64, November 2005. Millimeter wave astronomy reveals the material in close contact with the black hole, allowing a measure of the intrinsic size of the source (probably an accretion disk) that surrrounds the central black hole.