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Basic Skills/ Definitions Quiz
What is the approximate chemical composition (by mass) with which all stars are born?
- Three quarters hydrogen, one quarter helium, no more than 2% heavier elements.
The total amount of power (in watts, for example) that a star radiates into space is called its
Luminosity.
For example, the luminosity of the Sun is 3.7 x 10 to the 26
th
watts.
According to the universe square law of light, how will the apparent brightness of an object change if its
distance to us doubles?
Its apparent brightness will decrease by a factor of 4.
Assuming that we can always measure the apparent brightness of a star, what does the inverse square law
for light allow us to do?
It allows us to calculate a star’s luminosity if we know its distance, or calculate its distance if we know its
luminosity.
If star A is closer to us than star B, then Star A’s parallax angle is:
Larger than that of star B. A larger parallax angle means the star is closer.
Ten parsecs is about:
32.6 light-years
If star A has an apparent magnitude of 3 and star B has an apparent magnitude of 5, which star is brighter in
our sky?
Star A. The magnitude scale is “backward” so that smaller numbers mean greater apparent brightness.
From hottest to coolest, the order of the spectral types of stars is:
OBAFGKM
Our Sun is a star of spectral type:
G
Astronomers can measure a star’s mass in only certain cases. Which one of the following cases might allow
astronomers to measure a star’s mass?
The star is a member of a binary star system. If we can measure the orbital properties of a star around its
companion, then we can measure the mass with Newton’s version of Kepler’s third law.
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only
by measuring their periodic Doppler shifts?
Spectroscopic binary
The axes on a Hertzsprug- Russel diagram represent:
Luminosity and surface temperature
What can we infer, at least roughly, from a star’s luminosity class?
It’s radius.

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