1. THE LIFE CYCLE OF STARS
Chapter 15 – 2
Part 1

2. TYPES OF STARS
A star can be classified as one type of star early in its life, and as a different type of star as it gets older.
A star is classified differently as its properties change.

3. The Life Cycle of Sun-like Stars
Like all natural cycles, the stages in a star’s life progress from birth to death.

4. Nebula or Protostars A star begins life as a ball of gas and dust.
Gravity pulls the materials into a sphere.
As the sphere gets denser, the temperature rises to 10,000,000* C.
Nuclear fusion occurs as hydrogen combines into helium.

5. Main-Sequence Stars
After a sun-like star forms, it enters the main-sequence.
This is the second and longest stage of its life.
Energy is generated in the core and causes the star to shine.
The size of the star changes very little as long as its supply of hydrogen nuclei fuse into helium nuclei.

6. Nuclear Fusion

7. Giants and Supergiants
When a main sequence star uses all its hydrogen in its core, helium begins to fuse.
The center then begins to shrink, and the atmosphere grows very large and cools.
ANTARES

8. White Dwarfs
A white dwarf is a small, hot, and dim star that is the leftover center of a red giant.
It slowly cools and becomes smaller, but can shine for a billion years.
SIRIUS

9. Let’s Review the Life Cycle of a Star
Nebula or Protostars
Main-Sequence Stars
Giants and Supergiants
White Dwarfs

10. LET’S TRY IT!
ACTIVITY: THE LIFE CYCLE OF STARS