Bob Moler's Ephemeris Blog

This is Ephemeris for Thursday, August 7th. Today the Sun will be up for 14 hours and 23 minutes, setting at 9:00, and it will rise tomorrow at 6:37. The Moon, 2 days before full, will set at 5:26 tomorrow morning.

The moon exhibits the same face to the Earth throughout the month. That doesn’t mean the Moon doesn’t rotate. It means that the moon rotates in the same time it takes to orbit the Earth. This is called synchronous rotation. It is also known as tidal locking, caused by the difference in the gravitational attraction across the body of the Moon from the near side to the far side. The same thing happens with the Earth and is best seen by the ocean tides on the part of the Earth facing and away from the Moon. The reason the Earth is not tidally locked is that it is much more massive. But the Moon is slowing down the Earth’s rotation. But by doing that, it is moving further away, so it will never totally lock the Earth’s rotation with it.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum