A planetary nebula has a radius of 0.5 pc and is expanding at 20 km/s. What is the approximate age of this planetary nebula? (1 pc is equal to 3×10^13 km and 1 year is equal to 3.15×10^7 seconds.)
a. 240 years
b. 790,000 years
c. 96,000 years
d. 960 years
e. 24,000 years
e
RATIONALE: age = radius/speed. Convert from seconds to years.
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