## Sections Review

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#### Vocabulary

absolute magnitude apparent magnitude filter
luminosity magnitude solar luminosity

#### Formulae

• Luminosity = (surface area of star) × flux of energy through its surface. This is: [4p×(star's radius)2] × [×(star's surface temperature)4], where is the Stefan-Boltzmann constant.
• Star A brightness = star B brightness × 2.512(mag B - mag A). Star B is the reference star.

#### Review Questions

1. What does a magnitude interval of 5 correspond to in brightness? How about an interval of 1? How about an interval of 3?
2. Do bright things have larger or smaller magnitudes than fainter things?
3. How is apparent magnitude different from absolute magnitude?
4. Put the following objects (given with their apparent magnitudes) in order of brightness as seen from Earth (faintest first): Sun (-26.7), Venus (-4.4), Barnard's Star (9.5), Sirius (-1.4), Proxima Centauri (11.0).
5. You receive 8× 10-9 Watts/meter2 of energy from a star 2 parsecs away with an apparent magnitude = 1.3. What is the energy you receive from a star with an apparent magnitude = 5.3?
6. Two identical stars but star B is 10X farther away than star A. What is the difference in magnitudes between the two stars?
7. What two things does luminosity depend on?
8. If our Sun has luminosity = 1 solar luminosity, what is the luminosity of the following stars if they have the same diameter as the Sun (fill in the table):
star temperature (K) luminosity
Sun 6,000 1
A 12,000
B 2,000
C 36,000
9. Some stars have temperatures of only 3000 K but have over 100X more luminosity than the Sun. How is this possible?
10. Would a red giant have a smaller or larger magnitude in a ``V'' filter than in a ``B'' filter? (Remember the first rule of magnitudes!)

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last updated: June 2, 2007