The band of light that we call the Milky Way is actually the plane of the disk of our galaxy. The Sun is one, rather faint, example of approximately 200,000,000,000 stars that make up our galaxy. These stars are mostly grouped into a flattened disk which has a bulge at its centre. The Sun is in this disk about two thirds of the way from its centre to its edge. When we look at the night sky we see the Milky Way when we look along the plane of this disk whereas when we look in other directions, out of the plane, we see far fewer stars.
There is a spherical component to our galaxy which contains very old stars and spherical clusters of old stars. These are often referred to as Population 2 objects. Population 1 being the objects found in the disk. The size of our galaxy is huge; light would take about 100,000 years to cross the Galaxy.
The adjacent
figure shows a
telescopic
view of the Milky Way in the constellation
Scorpius.
The center of the galaxy
is in the left middle of this figure, but it is obscured by the gas and dust
lying between us and the center (the dark bands in the figure).
Thus, in visible light we cannot see the center of the galaxy.
However, visible light is not the only wavelength at which modern astronomers
can make observations. The image below is taken in the infrared (IR)
region of the
electromagnetic spectrum.
Unlike
visible light, which is strongly absorbed by the intervening
gas and dust,
the infrared light is transmitted well enough to give
us a clear view of the central region.
Thus, we see the side of the bulge surrounding the
galactic core
from
our position in the disk of the galaxy about 30,000 light years from the
center.
Based on information in:
Science and Engineering Research Council
Royal Greenwich Observatory
Information Leaflet No. 30: `Galaxies'.
Produced by the Information Services Department of the Royal Greenwich
Observatory.
PJA Wed Nov 24 17:27:41 GMT 1993
webman@mail.ast.cam.ac.uk
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