Stars are collections of dust and gas held together by gravity. They can be classified based on characteristics like temperature, luminosity, type, spectral class, and size. The main types of stars are main sequence, dwarf, giant, and supergiant stars. Nuclear fusion is the process by which stars generate energy by fusing hydrogen into helium. A star typically begins as a stellar nebula, collapses under gravity, and progresses through stages as a red giant or supergiant before exploding as a planetary nebula or supernova, eventually becoming a white dwarf, neutron star, or black hole.

1. Stars Extension Project- Extra
Credit By: Liling Class: L

2. Star and Categories
 What is a star? A star is a collection of duct and gas in ball
form that is gathered together by gravity.
 What are the characteristics? The characteristics are stars are
temperatures, luminosity, types of stars and spectral class
and sizes which we can use to classified the stars.

3. Characteristics
Temperature: how hot is it.
Luminosity: how bright is it.
Types of stars: Main Sequence, Giant, Supergiant, Dwarf
Spectral class: O,B,A,F,G,K,M (from hottest to coldest)
Sizes: how large is it.

4. Types of stars
 Main Sequence: A major grouping of stars that transfer hydrogen into
energy, it has longest period in a stars lifetime.
 Dwarf: A star has low mass, small size and average or below luminosity.
 Giant: bigger than main sequence and hotter than main sequence but with
the same surface temperature.
 Supergiant: most massive (big) and brightest stars

5. H-R Diagram & Nuclear Fusion
H-R Diagram is a graph that classified the stars according to sizes, types of
stars, temperature, color and luminosity.
Nuclear Fusion is a process that transfer 2 hydrogen molecules into 1 helium
molecule, it creates energy.

6. Life of a star

7.  Stellar Nebula- a collection of dust and gas that it gathered together by
gravity.
 Then collection of gas and dust get closer and closer formed either massive
star or average star.
 AS it gets closer the surface gets colder that formed either red giant or red
supergiant.
 Red giant explodes and becomes Planetary Nebula/ Red Supergiant
explodes and becomes supernova.
 Planetary Nebula becomes White Dwarf when it gets smaller and lose it
light. It becomes Black Dwarf that it’s dead.
 Supernova becomes either Neutron star (the star that spin) or black hole (it
stuck everything in and everything inside is disappeared).