This is a thought question. Why are few galaxies outside our own galaxy seen by our eyes in the circle around the sky where the Milky Way is located? This is because
a. there aren't any galaxies in those directions.
b. dust in the Milky Way blots out our view of galaxies in those directions.
c. the missing mass is in those directions.
d. a massive explosion has blown galaxies away from those directions.
Question 2The lowest-mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
a. 1 solar masses.
b. 80 solar masses.
c. 8 solar masses.
d. 0.08 solar masses.
e. 0.001 solar masses.
Question 3The disk of our galaxy consists of
a. the nine known planets.
b. only stars.
c. stars, dust, and gas.
d. quasars.
e. only black holes.
Question 4Due to the dust in the interstellar medium, a distant star will appear to an observer on Earth to be
a. brighter and cooler than it really is.
b. brighter and hotter than it really is.
c. fainter and cooler than it really is.
d. fainter and hotter than it really is.
e. unchanged in brightness or apparent color.
Question 5The energy source at the center of our galaxy is called
a. Cygnus X-1.
b. the Orion arm.
c. the Sun.
d. Sagittarius A.
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