Suppose that a planetary nebula is 0.5 parsecs in diameter and expanding at 20 km/s.How old is it? (Hint: 1 pc = 3.1*10¹³ km.)

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Quizplus · Accepted Answer

To find the age, use the formula: age = distance / speed. The diameter is 0.5 parsecs, so the radius is 0.25 parsecs. Convert 0.25 parsecs to km: 0.25 * 3.1 x 10^13 km/pc = 7.75 x 10^12 km. Then, divide by the expansion speed: 7.75 x 10^12 km / 20 km/s = 3.875 x 10^11 seconds. Convert seconds to years: 3.875 x 10^11 s / (60 s/min * 60 min/hr * 24 hr/day * 365.25 days/yr) ≈ 12,000 years.

Suppose That a Planetary Nebula Is 0