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.
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.
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.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.