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03/12/2019 – Ephemeris – Does the Moon rotate?

March 12, 2019 Comments off

Ephemeris for Tuesday, March 12th. Today the Sun will be up for 11 hours and 43 minutes, setting at 7:44, and it will rise tomorrow at 7:59. The Moon, 2 days before first quarter, will set at 2:00 tomorrow morning.

Since we see only one face of the Moon throughout the month does that mean that the Moon doesn’t rotate? It doesn’t appear to rotate with respect to the Earth, but the Moon rotates through all the stars and constellations of the zodiac in a 27.32 days. That’s called a sidereal month. The lunar month we’re more familiar with is the synodic month, or lunation, that lasts 29.53 days which is the interval between new moons. It is the basis of the Jewish and Islamic calendars. The reason for the locking of the Moon’s rotation and revolution of the Earth, also called synchronous rotation, is the tidal pull of each on the other. The Earth has managed to slow the Moon’s rotation to match its revolution. The Moon is trying to do the same to the Earth with much less success, though every year or two a second is added to the time stream, UTC1 or Greenwich Mean Time, due to the slowing of the Earth’s rotation.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Moon rotation/revolution animation

Animation of the Moon orbiting the Earth showing the Moon’s rotation. Credit: NASA’s Scientific Visualization Studio/Ernie Wright, modified and converted to GIF by Bob Moler.

NASA’s Scientific Visualization Studio web page where I got the original for the above video.