Enjoying EarthSky? Subscribe.

264,570 subscribers and counting ...

1st quarter moon is February 23

A first quarter moon rises around noon and sets around midnight.

Elizabeth Worthy Clark caught the first quarter moon as it was setting on February 23.

This month’s first quarter moon comes on February 23, 2018, at 08:09 UTC (2:09 a.m. CST); translate UTC to your time. A first quarter moon rises around noon and sets around midnight. That means the February 22 moon is actually a bit closer to first quarter for us in North America. No matter where you are on Earth, watch for the moon on February 22 or 23. It’ll be half-illuminated (or nearly so), looking like half a pie – in late afternoon or evening.

At first quarter moon, the near side of the moon – the part we see – is half-illuminated by sunlight and half-immersed in the moon’s own shadow. In other words, we’re seeing half the moon’s day side.

Tom Wildoner caught this photo of the moon on November 26, 2017, and wrote: “One of my favorite areas to photograph on the moon near the first quarter! I captured this view of the sun lighting up the mountain range called Montes Apenninus. The moon was near the 1st quarter phase on the evening of November 26, 2017, casting a nice shadow on the backside of the mountains. This mountain range is about 370 miles (600 km) long with some of the peaks rising as high as 3.1 miles (5 km).”

Here’s something else to look for on a 1st quarter moon. Aqilla Othman in Port Dickson, Negeri Sembilan, Malaysia, caught this photo on May 3, 2017. Notice that he caught Lunar X and Lunar V. These are similar features on the moon that fleetingly take an X- or V-shape when the moon appears in a 1st quarter phase from Earth.

We call this moon a quarter and not a half because it is one quarter of the way around in its orbit of Earth, as measured from one new moon to the next. Also, although a first quarter moon appears half-lit to us, the illuminated portion we see of a first quarter moon truly is just a quarter. We’re now seeing half the moon’s day side, that is. Another lighted quarter of the moon shines just as brightly in the direction opposite Earth!

Here’s a closer look at Lunar X and Lunar V. Photo taken May 3, 2017, by Izaty Liyana in Port Dickson, Negeri Sembilan, Malaysia. What is Lunar X?

And what about the term half moon? That’s a beloved term, but not an official one.

A first quarter moon rises at noon and is highest in the sky at sunset. It sets around midnight. First quarter moon comes a week after new moon. Now, as seen from above, the moon in its orbit around Earth is at right angles to a line between the Earth and sun.

Four keys to understanding moon phases

Deborah Byrd