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Chapter 15 Surveying the Stars

Chapter 15 Surveying the Stars. How do we measure stellar luminosities?. The brightness of a star depends on both distance and luminosity. Luminosity: Amount of power a star radiates (energy per second = watts) Apparent brightness: Amount of starlight that reaches Earth

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Chapter 15 Surveying the Stars

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  1. Chapter 15Surveying the Stars

  2. How do we measure stellar luminosities?

  3. The brightness of a star depends on both distance and luminosity.

  4. Luminosity: Amount of power a star radiates (energy per second = watts) Apparent brightness: Amount of starlight that reaches Earth (energy per second per square meter)

  5. Clicker Question Alpha Centauri and the Sun have about the same luminosity. Which one appears brighter? A. Alpha Centauri B. The Sun

  6. Clicker Question Alpha Centauri and the Sun have about the same luminosity. Which one appears brighter? A. Alpha Centauri B. The Sun

  7. Luminosity passing through each sphere is the same App Brightness = Luminosity 4π D2 This formula is used to find stellar distances, D, once the luminosity & apparent brightness is known.

  8. Clicker Question How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright. B. It would be only 1/6 as bright. C. It would be only 1/9 as bright. D. It would be three times brighter.

  9. Clicker Question How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright. B. It would be only 1/6 as bright. C. It would be only 1/9 as bright. D. It would be three times brighter.

  10. Parallax is one technique used to find distance of nearby stars.

  11. Parallax is the apparent shift in position of a nearby object against a background of more distant objects.

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