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First quarter moon on May 2

A first quarter moon appears half-lit from Earth. It rises at noon, and is highest at sunset.

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.

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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 May 3, 2017 at 02:47 UTC. For North American time zones, that translates to May 2 at 11:47 p.m. ADT, 10:47 p.m. EDT, 9:47 p.m. CDT, 8:47 p.m. MDT, 7:47 p.m. PDT, 6:47 p.m. AKDT and 4:47 p.m. HAST.

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 the moon appears half-lit to us, the illuminated portion of a first quarter moon truly is just a quarter. On the night of first quarter moon, we see half the moon’s day side, or a true quarter of the moon. 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.

When the first quarter moon sets around midnight, the sun is below your feet. See? Good time to get a 3-D sense of the moon as a world in space, always half-illuminated by the sun. Animation created from images of setting first quarter moon, June 12, 2016, by Peter Lowenstein in Mutare, Zimbabwe.

When the first quarter moon sets around midnight, the sun is always below your feet. Good time to experience the moon and Earth as worlds in space, always half-illuminated by the sun. Setting first quarter moon by Peter Lowenstein in Mutare, Zimbabwe.

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

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