The Moon’s terminator is on full display tonight

With the Last Quarter Moon waning, tonight is a great night to observe the Moon's crisp dividing line between day and night.
By | Published: October 31, 2018 | Last updated on May 18, 2023
This image of a nearly half-lit Moon zooms in on the “Lunar X,” which is a clair-obscur effect caused by the interplay of light and shadows along the lunar terminator.
Dariome/Wikimedia Commons
Last Quarter Moon occurs at 12:40 p.m. EDT tonight.

By the time the Moon rises in North America shortly after midnight local daylight time, its phase will have waned to approximately 43 percent lit. Earth’s satellite currently sits near the border between Cancer the Crab and Leo the Lion.

The Moon also reaches perigee, the closest point in its orbit around Earth, at 4:23 p.m. EDT today. It then lies 230,034 miles (370,204 kilometers) away from us. Because the half-lit Moon sits closer to Earth than usual during perigee, it appears slightly larger than normal.

Tonight’s combination of a bright (but not overbearing) and relatively nearby Moon makes this evening a perfect night to seek out the lunar terminator — the line that divides day and night on the surface of the Moon.

Because our satellite does not have an atmosphere, scattered sunlight does not significant blur the terminator line like it does on Earth. This means the Moon’s nightside is exceptionally dark, while its dayside is easily visible, and the line that divides them is quite obvious.

With decent binoculars or a small telescope, seek out the terminator to spot breathtaking surface features, which stand out in sharp relief thanks to the interplay of light and dark along lunar crater rims.

If you manage to snap a picture of the terminator tonight, don’t forget to add it to our reader gallery!

For more observing targets, check out our weekly guide: The sky this week for October 26 to November 4.