Stellar masses are measured directly by observations of the motions of
A) spectroscopic binary systems.
B) visual binary systems.
C) eclipsing binary systems.
D) All of the above can give us their masses.
E) Stellar masses cannot be measured directly by any method.
D
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An observer's nadir is:
A) the point directly opposite the observer's zenith. B) the north point on the observer's horizon. C) directly opposite the north celestial pole. D) the south point on the observer's horizon.
Fraunhofer lines are apparent in
A) absorption spectra. B) emission spectra. C) Doppler shifts. D) a variety of energy levels. E) none of the above
What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
A) It marks the time at which the expansion of the universe had settled down to its current rate. B) The basic chemical composition of the universe had been determined. C) It marks the time at which the first stars formed. D) The proportions of dark matter and luminous matter had been determined.
An object 4 cm high is placed 15 cm in front of a convex mirror with a focal length of ?10 cm. What is the image position (in cm)?
a. ?8 b. ?4 c. ?2 d. ?6 e. 30