Geography: Milky Way Galaxy

Star Struck
Astronomers turn their telescopes to the unbounded beauty of the Milky Way...

Milky Way Galaxy is the galaxy in which the Solar System is located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies.The Milky Way galaxy has a whopping circumference of roughly 250-300 thousand light years. Within the main body of the Milky Way there are estimated to be between 200 and 400 billion stars.

All the stars that the eye can distinguish in the night sky are part of the Milky Way Galaxy, but aside from these relatively nearby stars, the galaxy appears as a hazy band of white light arching around the entire celestial sphere. The center of the galaxy lies in the direction of Sagittarius, and it is here that the Milky Way looks brightest. From Sagittarius, the Milky Way appears to pass westward through the constellations of Scorpius, Ara, Norma, Triangulum Australe, Circinus, Centaurus, Musca, Crux, Carina, Vela, Puppis, Canis Major, Monoceros, Orion and Gemini, Taurus, Auriga,Perseus, Andromeda, Cassiopeia, Cepheus and Lacerta, Cygnus, Vulpecula, Sagitta, Aquila, Ophiuchus, Scutum, and back to Sagittarius. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the Solar System lies close to the galactic plane. The galactic plane is inclined by about 60 degrees to the ecliptic (the plane of the Earth's orbit).

Every star in the Milky Way revolves around this black hole, named Sagittarius A* (abbreviated "Sgr A*" and pronounced "Sagittarius A-star"). The sun, 27,000 light-years away, completes a revolution once every 230 million years. Within just a light-year of the black hole swarm more than 100,000 other stars caught far more firmly in its grip. Some take only a few years to complete their orbits. These paths reveal that Sgr A* is four million times mass of the sun, somewhat more massive than had been thought a decade ago.