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The Milky Way is the galaxy that contains our Solar System. This name derives from its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars.
The Milky Way is a
barred spiral galaxy 100.000-120.000 light years in diameter
constraining 200-240 billion stars. The Solar System is
located within the disk, around two thirds of the way out
from the Galactic Center, on the inner edge of a
spiral-shaped concentration of gas and dust called
the Orion–Cygnus Arm. The stars in the inner ≈10,000
light-years are organized in a bulge and one or more bars.
The very center is marked by an intense radio source
named Sagittarius A* which is likely to be a supermassive
black hole. Stars and gas throughout the Galaxy rotate about
the center and the rotational period is about
200 million years. The Galaxy
as a whole is moving at a velocity of 630 km/sec, depending on the relative frame of reference. It is
estimated to be about 13.2 billion years old. |
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