Stellar Evolution and Classification

Twinkle, twinkle, little star,
How I wonder what you are.
Up above the world so high,
Like a diamond in the sky.
Twinkle, twinkle, little star.
How I wonder what you are.
How I wonder what you are.

"Twinkle, Twinkle, Little Star"
by Jane Taylor

Astronomers study stars to answer these same questions presented in this popular children's lullaby. All stars form from stellar nurseries called nebulae. Here, gases are compressed, the core of the star forms, and fusion begins. All stars create energy through the process of nuclear fusion. A star's hydrogen fuses into helium under intense pressure, and this creates helium and light energy. Eventually, stars either use up all of their hydrogen gas or release it back into space. The released gas will form a nebula and eventually be re-condensed into another star. In a way, stars recycle themselves. How quickly or slowly a star goes through its life will depend in its composition. A lot of information about a star's life cycle can be determined by investigating the elements that make it up.

Essential Questions

• How and where do stars form?
• What are the different stages of evolution for high and low mass stars?
• How are stars distributed in space?
• How do scientists determine the distance of stars from Earth?