A Star is a burning ball of gas. There are billions of stars in the universe that come in many different sizes and burn at different rates. Our sun is a medium sized star. The life of stars is related to their size, large stars burn brightly and die young.
There are seven types of star classified by their spectra (the elements that they absorb) and their temperature:
Alpha Centuri is the closest star to the Solar System
ESO/Digitized Sky Survey 2 - Acknowledgement: Davide De Martin
- O - He II absorption;
- B - He I absorption;
- A - H absorption;
- F - Ca II absorption;
- G - strong metallic lines;
- K -bands developing;
- M - very red.
O and B stars are the hottest and very bright but very uncommon. M types stars are dim and the coolest and the most common.
The Sun is a G1 star.
Stars are not uniformly distributed amongst the universe. They are clumped together in big galaxies by gravity.