What is a Light Year?
- The distance that light travels in one year
- Or 9.5 trillion km
- 300,000 km. every secound
- The Milky Way Galaxy is about 100,000 light years in diameter
- Proxima Centauri is the closert star to us at about 4.3 light years away
- 1 parsec = 3.26 light years
- Commonly used unit in astronomy
Stars
- A massive, luminouns (bright) sphere of plasma held together by its own gravity.
Life cycle of a star
1. stars are formed inside of a nebula (hoge clouds of dust that collapse under gravitational forces)
2. As the dust and gasses collapes under their own pressure stars are formed
3. As they grow older the gas inside (He and H) runs out causing the core to expand and the star to grow less bright
4. The star will eventually collapse or exphode under its own gravity creating cither a white dwerf, neutron star or black hole
which it forms depends on the stars original mass