A big cluster of space where stars are found is called galaxy. 1011 galaxy are spread in the universe, each of it contains about 1011 stars. So, it total, there are about 1022 stars in the universe. Generally, galaxies are shaped either spiral or elliptical. Spiral galaxies are more in number than elliptical galaxies. However, some galaxies are in irregular shapes.
The age of stars can be indicated from the color. In elliptical galaxies, most stars are red, demonstrating their very old age. Meanwhile, in spiral galaxies, most stars are bluish, representing their young age. From this point of view, it is fair to say that spiral galaxies are younger than elliptical ones.
Our solar system is situated on a galaxy called Milky Way. It is called so because it looks like a belt of milk which extends from North to South when the sky looks clear in the dark night. If you view from the top, Milky Way is spiral. However, if it is seen from the side, it looks bulging in the middle, and narrowed toward the edges.
Milky Way has the diameter of about 1 lac (equal to 0.1 million) light years. Meanwhile, the bulging part has the thickness of about 15000-20000 light years. Sun with its gigantic solar system is situated on about 3000 light years from the center of Milky Way.
The Sun completes a revolution toward the center of the galaxy in 22.5 years at the speed of 250 kilometer/s.
