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.) 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. 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 Nuclear Fusion  combining atomic nuclei to form heavier elements Which two elements are most stars composed of? Hydrogen and Helium 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 Apparent: how bright stars “appear” from Earth Absolute: how bright a star really is. Absolute: how bright a star really is.

Motion of Stars Apparent (Earth’s rotation) vs. Absolute (expanding universe)

Motion of Stars Red-Shift: stars “appear” more red as they move away from us. (This is one piece of evidence that the universe is still expanding since the “Big Bang”) Red-Shift: stars “appear” more red as they move away from us. (This is one piece of evidence that the universe is still expanding since the “Big Bang”) Click Ambulance to hear Doppler sound-effect Doppler Effect: and 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. 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.

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