1. Properties of Stars: Brightness (37)

2. Remember… We have learned how to determine a star’s: We have learned how to determine a star’s: –Chemical Composition. –Direction of Motion –Speed of Motion But to fully understand a star we also need to know: But to fully understand a star we also need to know: –How much energy does it emit? (luminosity) –How big is it? (volume) –How much matter does it contain? (mass)

3. Ways to Describe Brightness Intrinsic Brightness (Good): total amount of light (energy) a star emits. Intrinsic Brightness (Good): total amount of light (energy) a star emits. –Measures amount of energy we receive on Earth. Flux: How many Joules per second hitting a square meter. Flux: How many Joules per second hitting a square meter. –1 J/s = 1 Watt (W). –Problem: Amount of flux/brightness received decreases with a star’s distance.

4. Ways to Describe Brightness (cont.) Absolute Visual Magnitude (Better): how bright a star is if it were seen 32.62 ly away. Absolute Visual Magnitude (Better): how bright a star is if it were seen 32.62 ly away. –Easy to find using apparent magnitude and distance from earth. –Problem: Based only on visible light. –Sun is 4.78. Would be no brighter than the Little Dipper’s faintest stars. Would be no brighter than the Little Dipper’s faintest stars.

7. Ways to Describe Brightness (cont.) Luminosity (Best): Luminosity (Best): –Measures TOTAL energy a star is emitting per second. –Absolute magnitude only measures visible light. –Hot stars emit more UV light, cooler stars emit more infrared light. –The sun’s luminosity = 4 X 10 26 W. This is called 1 Solar Luminosity. This is called 1 Solar Luminosity.

8. Star Brightness Ad (36) Create an advertisement for one of the science concepts we just discussed. Create an advertisement for one of the science concepts we just discussed. Your ad should incorporate ideas about the concept to convince people why they should “buy” it. Your ad should incorporate ideas about the concept to convince people why they should “buy” it. Be sure to include an eye-catching illustration that relates to the concept. Be sure to include an eye-catching illustration that relates to the concept. Write 4-6 sentences explaining how your ad and illustration relate to the concept you have chosen. Write 4-6 sentences explaining how your ad and illustration relate to the concept you have chosen.