1st quarter moon is December 15

The 1st quarter moon comes on December 15 at 11:49 UTC. A 1st quarter moon is high up at sunset. It appears half-illuminated, like half a pie. Really, you’re seeing half the moon’s day side.

Nearly first quarter moon from Suzanne Murphy in Wisconsin.

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A first quarter moon rises around noon and sets around midnight. You’ll likely spot it in late afternoon or early evening, high up in the sky. At this moon phase, the moon is showing us precisely half of its lighted half.

Or you might say that – at first quarter moon – we’re seeing half the moon’s day side.

The December 2018 1st quarter moon will be near Mars. Watch for them shortly after sunset and into the early evening.

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!

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

Tom Wildoner 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. 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.

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

As the moon orbits Earth, it changes phase in an orderly way. Follow the links below to understand the phases of the moon.

New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Last quarter moon
Waning crescent moon

Read more: 4 keys to understanding moon phases

Here’s a 1st quarter moon – in a hazy blue sky, before sunset – over Toronto, via Steven A. Sweet of Lunar 101-Moon Book.

Bottom line: The first quarter moon comes on December 15 at 11:49 UTC; translate UTC to your time. As viewed from the whole Earth, it’s high up at sunset, looking like half a pie.

Check out EarthSky’s guide to the bright planets.

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Deborah Byrd

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