Star

1. What is a star?
A star is a big gas ball. They have different colors, size, temperature and luminosity. The star made of gas and dust.

2. Types of Stars.
The four main types of stars- Whiter dwarf, Main Sequence, Giant, Super Giant. The characteristics of stars is  ages, size, temperature, luminosity, color and spectral class.
Ages- Young Stars, Middle Age Stars, Old Stars
Size- Small Stars, Medium Stars, Large Stars
Temperature- Hot Stars(30000°-10000°), Medium Stars(10000°-4000°), Cold Stars(4000°-2000°)
Luminosity- Bright Stars(100000-100), Medium Stars(100-0.1), Dim Stars(0.1-0.0001)
Color- Blue, Blue- White, White, White- Yellow, Yellow, Orange, Red
Spectral class- O B A F G K M

3. H-R Diagram
H-R Diagram is a graphical tool that astronomers use to classify stars according to their temperature, luminosity, color, spectral types and evolutionary stage.

4. Nuclear Fusion
Nuclear Fusion is two Hydrogen gas molecules into a Helium molecule inside the stars. The nuclear fusion is create the star energy. H+H=He

5.The Life Cycle of a star
First, all the star is born are Stellar Nebula. The stellar nebula is a cloud giant star. There have 3 different types star. Is the Sun-Like Star,Huge Star, Giant Star.
Sun-like star is born with Stellar Nebula, then become Red Giant, Planetary Nebula, White Dwarf, and last is Black Dwarf.
Huge Star is born with Stellar Nebula, then become Red Supergiant, Supernova， and last is Neutron Star.
Giant Star is with Stellar Nebula too, then become Red Supergiant, Supernova，and last become a Black Hole