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Where’s the moon? 1st quarter

The second of this month’s two first quarter moons comes on July 30, 2017. It’ll appear half-illuminated and to the east of the dazzling planet Jupiter!

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 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.

This waxing moon and upcoming full moon will interfere with the 2017 Perseid meteor shower. That’s why we’re recommending that you watch meteors this weekend, or in the coming week.

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.

The Earth and moon are like mirrors to each other. If you were on the moon at its last quarter phase, you’d see a last quarter Earth. Simulation of last quarter Earth as viewed from 1st quarter moon (2017 July 30 at 15:23 UTC). The terminator or shadow line represents Earth’s line of sunsets. Image via Fourmilab.

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.

On July 29 and 30, 2017, the moon’s lit side points in the direction of the planets Jupiter and Mercury. Read more.

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

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