Prior Knowledge Questions (Do these BEFORE using the Gizmo.) How do the appearances of stars A, B, and C in the photo at left compare? What are some ways the stars in the photo could be grouped or classified?

Chapter 29

“ Characteristics of Stars” Objectives: Describe how astronomers determine the composition & surface temperature of a star. Explain why stars appear to move to an observer on the earth. Name & describe the way astronomers measure the distance from the earth to the stars. Explain the difference between absolute magnitude & apparent magnitude.

Star Composition All stars create light from Nuclear Fusion Hydrogen + Hydrogen = Helium Also may contain: Carbon Oxygen Nitrogen Calcium

How do we know what’s in a star?

1 because of gravity 2 10,000,000 C 3 red supergiant 4 black holes 5 neutron star 6 red giant 7 planetary nebula 8 brown dwarf/black dwarf

Motion of Stars 1- Apparent Motion circumpolar

2- Actual Motion Rotate on their axis Revolve around another star Move toward or away from the earth

Omega Centauri

Measuring Distance in Space Use 1 Light-year = 9.5 trillion km Remember the SUN is 8 light-minutes away The next closest star is 4.2 light-years away Polaris is 700 light-years away Astronomers use PARALLAX to calculate distance in space

PARALLAX

Huge distances in space Measured in parsecs (pc) Parsec= 3.26 light years= 3.086 x 1013 km

Stellar Magnitudes Depends on the stars brightness & its distance from space 2 scales can be used Apparent Magnitude: How it looks from Earth Sun  Moon  Venus  Jupiter  Saturn  Sirius Absolute Magnitude: Also called luminosity How it would look if we were 10 parsecs away. “BeetleJuice”  Rigel  Spica  Sirius

Apparent Magnitude

Absolute Magnitude