One light-year is the distance light travels in one year. The speed of light is about 300,000 km/s . How far is 1 light-year?
A) 1.08 billion km (1,080,000,000, or 1.08 109 km)
B) 300 thousand km (300,000, or 3 105 km)
C) 9.46 trillion km (9,460,000,000,000, or 9.46 1012 km)
D) 18 million km (18,000,000, or 1.8 107 km)
Question 2
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is massive enough to become a star?
A) the central object becoming hot enough to sustain nuclear fusion in its core
B) a critical fraction of the gas has been driven further into space
C) nothing; all collapsing gas clouds become black holes
D) the crowding of electrons in the core
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