Milky Way
Milky way is the galaxy that contains our solar system. Its name derived from its appearance as a dim glowing band arching across the night sky whose individual stars cannot be distinguished by the naked eyes. From the earth , the Milky Way is appears as a band because it's disk shaped structure viewed within; Edwin hubble showed that the Milky Way is just one of many galaxies- now estimated 200 billion.
It is a barred spiral galaxy-that has a diameter usually considered to be 100,000-120,000 light years. But may be 130,000 -180,000 light years. The milky Way is estimated to contain 100-400 billion stars.
The solar system is located within the disk, about 27,000 light years from the galactic center, on the inner edge of one of the spiral shaped concentrations of gas and dust called the orion arm. The very centre is marked by an intense radio source, sagittarius A*, which is likely to be a supermassive black hole. Much of the matter of the Milky Way doesn't emit or absorb radiation and called dark matter. The rotational period is about 240 million years at the position of the sun. The Milky Way as whole is moving at a velocity of approximately 600 km/second with reference to extra galactic frames of reference.
The milky way has several satellite galaxies and is part of the local group of galaxies, which is a component of the virgo supercluster, which is itself a component of the laniakea supercluster.
dark regions within the band, such as the great rift and coalsack are areas where light from the distant stars is blocked by interstellar dust.
The area of the sky obscured by the milky way is called the zone of avoidance. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the milky way to be seen.
Mass of the milky way is 5.8× 10^11 solar mass (solar mass= 1.98 × 10^30 kg), less than andromeda galaxy.
references and for more
physical geography by savindra singh
