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.
- What does a magnitude interval of 5 correspond to in brightness?
How about an interval of 1? How about an interval of 3?
- Do bright things have larger or smaller magnitudes than fainter things?
- How is apparent magnitude different from
absolute magnitude?
- 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).
- 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?
- Two identical stars but star B is 10X farther away than star A. What is
the difference in magnitudes between the two stars?
- What two things does luminosity depend on?
- 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 |
|
- Some stars have temperatures of only 3000 K but have over 100X more luminosity
than the Sun. How is this possible?
- 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
Is this page a copy of Strobel's
Astronomy Notes?
Author of original content:
Nick Strobel