Enjoying EarthSky? Subscribe.

253,190 subscribers and counting ...

Where’s the moon? 1st quarter

It officially comes on June 1, but, if you live in the Americas, watch for a nearly 1st quarter moon on the night of May 31. It’ll appear almost half-illuminated from Earth.

Our friend Patrick Casaert of the Facebook page La Lune The Moon caught the moon on May 1, 2017, when it was nearly 1st quarter.

A first quarter moon shows half of its lighted hemisphere – half of its day side – to Earth.

The moon reaches its first quarter phase on June 1, 2017 at 12:42 UTC; translate UTC to your time zone.

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 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.

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.

On June 1, 2017, as evening falls in the western hemisphere, the moon will be slightly past the first quarter phase, but it’ll be near some bright planets and stars. The charts below explain more:

On the night of June 1, 2017, the moon is located to the east of the bright star Regulus in the constellation Leo the Lion.

Extend the line of the ecliptic – or sun’s path – further east on June 1, 2017, and you’ll come to Jupiter, now the brightest starlike object in the evening sky. It shines close to Spica, the constellation Virgo’s brightest star. Spica and Regulus serve as “fixed” reference points to the whereabouts of the ecliptic on the sky’s dome; that is, they’re there on June evenings when the planets and moon move away.

Extend the line of the ecliptic – or sun’s path – even further east on June 1, 2017, and you’ll come to the stars Zubenelgenubi and Antares. Keep going – nearly all the way to the eastern horizon – and you’ll find the bright planet Saturn.

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