Lesson No. 5

Introducing Universe, Galaxy and Milky way and Sun (stars and planets)

Topic – 20: Galaxy and Milky Way:

Galaxy

It is the system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

Milky Way

The Milky Way is the galaxy that contains our Solar System. Its name “milky” is derived from its appearance as a dim glowing band arching across the night sky whose individual stars cannot be distinguished by the naked eye. There are probably more than 100 billion galaxies in the observable Universe. A galaxy range from ten million stars up to one trillion stars. Most galaxies vary from about 10,000 to 200,000 light years in diameter, and are usually grouped in clusters of 20 to several

thousands. The Clusters are grouped in Super clusters. The Milky Way is our home galaxy, is roughly 100,000 light years in diameter, and contains our solar system. This galaxy has 100–400 billion of stars and planets as well. Galaxy is an assemblage of stars, planets and other space material in a disc like shape. The diameter of a galaxy varies; distance between two neighboring galaxies is 3

million light-years. Its name “milky” is derived from its appearance as a dim glowing band arching across the night sky, cannot distinguish individual stars. The Solar System is located within the Milky Way, about 27,000 light-years away from the center of the galaxy. Stars and other material are orbiting at approximately 220km/sec around the center of the galaxy.