galaxy

• a galaxy is a vast system of billions of stars,which also contains a large number of gas cloud(mainly of hydrogen gas) and dust,isolated in space from similar system.

• there are about 100 billion galaxies (10^11 galaxies) in the universe,and each galaxy has on average 100 billion stars(10^11 stars). so the total number of stars in the universe is 10^22 stars.

• the milky way galaxy is the home of the earth and our solar system. it is spiral in shape.

• milky way galaxy was formed 5 billion years after the big bang.

• latest known galaxy is the dwarf galaxy.

• according to the modern thought, universe can be classified into two parts

         1) atmosphere

         2) space

• origin of the universe is explained by the big bang theory, formulated and proposed by the belgian astronomers and cosmologists georges lemaitre.

• andromeda is our nearest galaxy.

• A large group of stars, dust and light gases, bound together by their own gravity is called a galaxy.

• There are 10^11 galaxies in the universe.

• We live on the outer edge of a spiral type of galaxy called the milky way which is about 100,000 light years in diameter and is rotating slowly.

• Earth’s galaxy: the milky way.

• The milky way is a large spiral-shaped galaxy.

• It spans about 100,000 light years across and is about 10,000 light years thick at the center.

• It is called the milky way because it appears as a soft glowing light of billions of stars. These stars are so far that they can be seen only in costellation, not separately.

• Galileo discovered that this band of light was produced by countless individual stars which a naked eye can not see.

• It takes about 250 million years to complete one revolution.