Transcript Chapter 30 Stars, Galaxies & Universe Characteristics of Stars What is a “Star”?  A ball of gases that gives off a tremendous amount.

Chapter 30
Stars, Galaxies & Universe
Characteristics of Stars
What is a “Star”?

A ball of gases that gives off a tremendous amount of
electromagnetic energy (x-ray, radio, light, etc.)
Are stars really “burning”?

No, they are extremely hot due to billions of nuclear reactions.
What type of Nuclear reactions?

Nuclear Fusion  combining atomic nuclei to form heavier elements
Which two elements are most stars composed of?

Hydrogen and Helium
Nuclear Fusion
Equilibrium
in a star is the
balance between
pressure from
nuclear reactions
pushing out and
gravity pulling in.
Nuclear Fusion
The energy constantly
being released by a
star is like millions of
atomic bombs going
off at the same time…
ALL the time!
Luminosity & Magnitude = Brightness
 Apparent: how bright stars “appear” from Earth
 Absolute: how bright a star really is.
Motion of Stars
Apparent (Earth’s rotation) vs. Absolute (expanding universe)
Motion of Stars
stars “appear” more red as
they move away from us. (This is one piece of
 Red-Shift:
evidence that the universe is still expanding since the “Big Bang”)
 Doppler Effect: Light and Sound travel in
waves like all forms of energy. Moving toward
you, the waves are pushed together, but going
away, they spread apart. This causes the pitch
of sound and color of light “appear” to change.
Click Ambulance to hear Doppler sound-effect
Hertzsprung-Russell (H-R) Diagram
This diagram compares the Temperature to Luminosity/Absolute Magnitude (or brightness) of
stars. Our sun is about average temperature and brightness for stars. This also represents the life
cycle of stars, growing from a nebula into Red Supergiants before collapsing into White Dwarfs
(or neutron stars). The center band or cluster is referred to as the "Main Sequence".
Life Cycle of a Star