If the synodic period of Mars is observed from Earth to be 2.1 years, what is Mars's sidereal period?
A) 5.3 years
B) 0.47 years
C) 1.9 years
D) 3.4 years
E) 0.69 years

Question

Quizplus · Accepted Answer

The synodic period is the time it takes for a planet to return to the same position relative to the sun and Earth. The sidereal period is the time it takes for a planet to complete one orbit around the sun relative to the distant stars. Therefore, we can use the equation 1/P = 1/S - 1/E, where P is the synodic period, S is the sidereal period, and E is Earth's sidereal period (1 year). Plugging in the given values, we get 1/S = 1/2.1 - 1/1 = 0.4762. Solving for S, we get S = 1/0.4762 = 2.1 years. Therefore, the answer is choice C, 1.9 years.

If the Synodic Period of Mars Is Observed from Earth