Galaxy
Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
A galaxy is a huge system of stars, gas and dust held together by gravity. Galaxies are about 80,000 to 150,000 light years across. They began to form because matter in the early universe was spread unevenly. Thicker patches had stronger gravity and pulled more matter in. Hydrogen gathered into giant clouds, and stars formed inside them.
Example
Our Sun is in the Milky Way, a barred spiral galaxy about 100,000 light years across. The Sun is about 26,000 light years from its centre. Andromeda is the nearest large galaxy.
Don't confuse with
- Nebula: a nebula is one cloud of gas and dust where stars are born. A galaxy holds billions of stars and many nebulae.
- Solar system: this is just the Sun and the bodies that go round it. It is a tiny part of one galaxy.