When Mercury is seen 18° from the Earth-Sun line, it will be visible a little less than 1 hour after sunset. What is the most important value in determining this time?
A)Mercury's rotation period about its axis
B)Mercury's sidereal period
C)Earth's rotation period about its axis
D)Earth's sidereal period

Question

Quizplus · Accepted Answer

The most important value in determining the time when Mercury is visible is Earth's rotation period about its axis, as this determines the timing of sunset and therefore the time when Mercury will be visible. The other values listed (Mercury's rotation period about its axis, Mercury's sidereal period, and Earth's sidereal period) are not directly relevant to determining the timing of Mercury's visibility after sunset.

When Mercury Is Seen 18° from the Earth-Sun Line, It