Archive for July 16, 2021

07/16/2021 – Ephemeris – The best time to see detail on the Moon (IMHO)

July 16, 2021 Comments off

This is Ephemeris for Friday, July 16th. Today the Sun will be up for 15 hours and 11 minutes, setting at 9:24, and it will rise tomorrow at 6:13. The Moon, 1 day before first quarter, will set at 1:08 tomorrow morning.

I consider the week centered on the first quarter moon to be the best time to view the Moon in a telescope. The best part of the Moon to view is near the terminator. The terminator is the sunrise line on the moon that we see before full moon, and the sunset line we see after full moon. The terminator is where the shadows are longest on the Moon and indeed on the Earth, with the low Sun in the sky. The Moon has lots of craters in its south or bottom part. We call that the lunar highlands, which is completely saturated with craters. Personally, I like craters. The darker lava plains that were initially called seas (the name stuck). They are flat and nearly featureless unless seen very close to the terminator, where the slight wrinkle ridges can be spotted.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.


The Moon tonight

The Moon tonight at 11 pm, July 16, 2021, about a day and 7 hours before the instant of first quarter. Note the shadows that bring out the craters near the terminator. Created using Stellarium.

Wrinkle ridges

Wrinkle ridges on the floor of a lunar sea (lava plain). These are only visible at a very low sun angle near the terminator. I can find no information on this image, but apparently it was taken in lunar orbit. This is much sharper detail than can be seen from earth.