Enjoying EarthSky? Subscribe.

263,066 subscribers and counting ...

Where’s the moon? 1st quarter

The moon reaches its first quarter phase on August 29 at 08:13 UTC. Full moon will be September 6. Is the September 6 full moon a Harvest Moon? Many will say yes! Others will say no.

Here’s what a first 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.

The moon reaches its first quarter phase on August 29, 2017, at 08:13 UTC. Full moon will be September 6 at 07:03 UTC; translate UTC to your time zone. Many will think of the September 6 full moon as the Harvest Moon, but others will say the Harvest Moon of 2017 falls in October. Read more about 2017’s Harvest Moon here.

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.

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