The moon last reached its first quarter phase on July 1, 2017, at 0:51 UTC, and will do so again this month on July 30, 2017, at 15:23 UTC. Full moon will be August 7 at 18:11 UTC; translate UTC to your time zone.
Also, this moon – waxing inexorably toward full moon and then to the waning moon phases and finally back to a new moon – will ultimately cover the sun in the much-anticipated total solar eclipse of August 21, 2017.
A first quarter moon shows half of its lighted hemisphere – half of its day side – to Earth.
The first quarter moon and the planet Mercury’s greatest evening (eastern) elongation both occur on the same date by Universal Time, on July 30, 2017. As darkness falls on July 30, let the moon guide you to the dazzling planet Jupiter – and possibly to Mercury, the solar system’s innermost planet. An imaginary line from the moon through Jupiter, the brightest starlike object in the evening sky, just might enable you to catch Mercury near the horizon at late dusk, as shown on the chart below.
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!
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.
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 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.