First Quarter Moon Appears Half-illuminated - EarthSky

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Moon, half illuminated.
View at EarthSky Community Photos. | Lorraine Boyd captured this from New York on November 9, 2024, and wrote: “Peeking through tree limbs at the first quarter moon (50% illumination), just after sunset.” Thank you, Lorraine.

First quarter moon

Here are the characteristics of a first quarter moon:

– It’s the moon phase halfway between new moon and full moon.

– It’s a waxing moon.

– As viewed from anywhere on Earth, a first quarter moon appears at its highest in the sky at sunset. It rises around noon and sets around midnight.

– It’s called a quarter moon, but, from Earth, it looks half-illuminated, like half a pie. Or you might say that – at first quarter moon – we’re seeing half the moon’s day side or a quarter of the whole moon.

Half-lit Earth from north, and half-lit moon with divisions between dark and light sides lined up.
As seen from the north side of the moon’s orbital plane, the terminators (lines between sunny and shadowed sides) of the Earth and moon align at first quarter moon, and only the near half of the moon’s day side is visible from Earth. Image via Wikipedia Commons. Click here to see the animation.
Half illuminated moon at 1st quarter.
View at EarthSky Community Photos. | Mohamed Mohamed of Tripoli, Libya, captured this great image of the first quarter moon on January 28, 2023. Thank you, Mohamed!

Quarter moon? Half moon?

There’s another reason we call this moon a quarter and not a half. It’s because it’s one quarter of the way around in its orbit of Earth, as measured from one new moon to the next.

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

Do you have access to a small telescope? Here are some telescopic sights to see on a first quarter moon:

Rupes Recta, or The Straight Wall, is best found on 8 days past new moon when the terminator falls across it.
Tom Wildoner in Weatherly, PA, captured this photo of Rupes Recta. He wrote: “Rupes Recta, a linear fault line, or rille, appears as a straight shadow during the first quarter phase of the moon giving it the nickname the Straight Wall. This fault has a length of about 68 miles (110 kilometers). The small (11 miles wide) crater Birt lies just to the west.” Thank you, Tom! Used with permission.
Close-up of a 1st quarter moon along the terminator with arrows pointing to the X and V regions.
View at EarthSky Community Photos. Frank Lu of Texas captured this image on February 5, 2025, and wrote: “Inspired by Deborah Byrd’s article in EarthSky’s Astronomy Essentials on Lunar V and Lunar X, I went out looking for the Lunar X and Lunar V on this 1st-quarter. I’m extremely pleased to find them.” Thank you, Frank!

More articles about moon phases

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

Bottom line: The first quarter moon occurs halfway between new moon and full moon. One quarter of the moon is visible from Earth, meaning that you see half of the daylit side of the moon, looking like half a pie.

Read more: Top 4 keys to understanding moon phases

Check out EarthSky’s guide to the bright planets

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