Suppose Mercury had 5-to-3 spin-orbit coupling and that its sidereal period remained 88 days, as now. An observer sees the Sun directly overhead in the Mercurian sky and then observes again from the same location 88 days later. Where will the Sun be in the sky? (Mercury, like Earth, rotates toward the east.)

Question

Quizplus · Accepted Answer

With a 5-to-3 spin-orbit coupling, Mercury rotates 5 times for every 3 orbits around the Sun. In 88 days (one orbit), Mercury would have rotated 5/3 of a full rotation. This means the Sun would appear to have moved eastward, ending up below the eastern horizon.

Suppose Mercury Had 5-To-3 Spin-Orbit Coupling and That Its Sidereal