Enjoying EarthSky? Subscribe.

271,746 subscribers and counting ...

Where’s the moon? 1st quarter

The moon reaches its 1st quarter phase on September 28 at 02:54 UTC. The upcoming full moon on October 5 will be the Northern Hemisphere’s Harvest Moon.

View larger. | Two hours on the September 25 waxing moon. If you look closely at the terminator line – the line between light and dark on the moon – you can see the lunar sunrise creeping slowly across the lunar nearside. This advancing lunar sunrise will bring us a straight terminator line – a 1st quarter moon – on September 27-28. Photo by Andy Bentley.

The moon reaches its first quarter phase on September 28, 2017, at 02:54 UTC. That is September 27 at 10:54 p.m. EDT; ; translate UTC to your time zone. The moon is now waxing toward full moon – and the Harvest Moon, or closest full moon to the September equinox – on October 5. Read more about 2017’s Harvest Moon here.

If you’ve been watching the moon at nightfall lately, you might have noticed its changing position relative to the star Antares and planet Saturn. The September 27-28 1st quarter moon points to Saturn. Read more.

A first quarter moon shows half of its lighted hemisphere – half of its day side – to Earth. At quarter moon, the moon’s disk is half-illuminated by sunlight and half-immersed in the moon’s own shadow.

Here’s what a 1st quarter moon looks like. The terminator line – or line between light and dark on the moon – appears straight. 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.

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

Four keys to understanding moon phases

Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase

Deborah Byrd

MORE ARTICLES