At what longitude is an observer who sees the last-quarter moon on his meridian when it is 12:00 noon local solar time at 75°W?
A) 165°W
B) 15°E
C) 15°W
D) 165°E
E) 75°E

Question

Quizplus · Accepted Answer

The last-quarter moon is on the observer's meridian at 6:00 AM local solar time, indicating it is 6 hours ahead of the sun. Since the Earth rotates 15° per hour, the observer at 75°W seeing the moon at noon (when it's actually 6:00 AM for the moon's position) is 90° (6 hours * 15°) west of the moon's position, placing them at 165°W.

At What Longitude Is an Observer Who Sees the Last-Quarter