Our Place in the Universe : The Milky Way

Our solar system is located within a galaxy known as the Milky Way. The Milky Way appears as a dim glowing band in the night sky in which the naked eye cannot distinguish individual stars. It appears like that because its disk shaped structure is viewed from within. In 1610, Galileo Galilei resolved the band of light into individual stars. 

The Milky Way is a barred spiral galaxy and there are about 100 - 400 billion stars in the Milky Way and astronomers believe there are about 100 billion planets in it too. A disk of gas and dust known as the interstellar medium fills the space between the stars. Our solar system is located about 27 000 light years away from the Galactic Centre of the Milky Way. At the very centre is Sagittarius A*, and intense radio source, which is believed to be a supermassive black hole.

It is believed that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass is known as "dark matter".

The Milky Way is a aprt of the Local Group which is a part of the Laniakea or the Local Supercluster.

Background light or stray light from the moon can greatly reduce the visibility of the Milky Way. It is very difficult to view the Milky Way from a city or a town, but it can be easily observed from a rural area. 

When we observe from the Earth, the visible region of the Milky Way occupies an area in the sky which consists of 30 constellations. The centre of the Milky Way is where the galaxy is the brightest, is located in the direction of the constellation Sagittarius.

The Milky Way which is the second largest galaxy in the Local Group is approximately 100,000 light years across and approximately 1000 light years thick. Most of the mass of the Milky Way appears to be dark matter, which only interacts in a gravitational way with other matter.