Enjoying EarthSky? Subscribe.

0 subscribers and counting ...

1st quarter moon is April 22

This 1st quarter moon will offer gorgeous telescopic views for those taking part in Astronomy Day. Then it’ll conveniently set, leaving the sky dark for this weekend’s Lyrid meteors.

Elizabeth Worthy Clark caught a 1st quarter moon as it was setting, in February 2018.

This month’s first quarter moon comes on April 22, 2018, at 21:46 UTC (4:46 p.m. CST); translate UTC to your time. A first quarter moon rises around noon and sets around midnight. It’ll be half-illuminated, looking like half a pie – in late afternoon or evening.

Thus on this Astronomy Day 2018 – on April 21 – the moon will be nearly first quarter. It’ll offer fantastic telescopic views along the lunar terminator, or line between light and dark on the moon.

Also, this first quarter moon will be setting in the middle of the night and so won’t interfere with the Lyrid meteor shower, whose peak morning is likely April 22.

Tom Wildoner caught this photo in November 2017. He wrote: “One of my favorite areas to photograph on the moon near the 1st quarter! I captured this view of the sun lighting up the mountain range called Montes Apenninus. The moon was casting a nice shadow on the back side 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 in May, 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.

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.

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 in May 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.

Bottom line: A first quarter moon rises at noon and is highest in the sky at sunset. It sets around midnight. First quarter moon comes on April 22, 2018.

Four keys to understanding moon phases

Deborah Byrd

MORE ARTICLES