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Why no eclipse of May 10 full moon

Image of May full moon via US Naval Observatory

Tonight – May 10, 2017 – the moon is full. Here’s something fun about this May full moon, and, in fact, about most full moons. That is, it won’t undergo an eclipse. In fact, the May 10 full moon swings a whopping 5o (10 moon diameters) north of the ecliptic, the plane of Earth’s orbit around the sun. So it misses being in Earth’s shadow by a wide margin.

Some full moons come closer to passing through Earth’s shadow – that is, closer to being in eclipse without actually doing so – but the fact is that most full moons fail to reside at the antisolar point, the point that’s directly opposite the sun. It’s only when the moon passes through or very close to the antisolar point that we see a total eclipse of the moon.

October 8, 2014 total lunar eclipse composite by Michele Whitlow.

The next two full moons – June and July 2017 – will pass to the north of the ecliptic and the antisolar point, too. So there will be no lunar eclipse in June or July 2017.

The August 2017 full moon will sweep less than one degree north of the ecliptic. The relatively close pass will bring the southern part of the lunar disk into the northern part of the Earth’s dark umbral shadow. So, if you’re on the right place on Earth, you’ll see a partial lunar eclipse on August 7, 2017.

It’ll come just two weeks before the much-anticipated total solar eclipse of August 21, 2017, first total solar eclipse to be viewed from the contiguous United States since 1979.

Read more: Why no eclipse at every full and new moon?

Worldwide map of the partial lunar eclipse on 2017 August 7 via EclipseWise. Although the August 2017 full moon will pass north of the ecliptic (dotted line) and the antisolar point (cross at center of red circle), the southern part of the lunar disk still will dip into the Earth’s dark umbral shadow (red circle), causing a partial eclipse.

This May full moon is the second full moon after the March equinox. In North America, we’ll call it the Flower Moon, Planting Moon or Milk Moon. Meanwhile, in the Southern Hemisphere, this full moon is called the Beaver Moon or Frost Moon.

Read more: What are the full moon names?

For general reference, we can say the moon is full all night. But, technically speaking, the moon is full only at the instant that it’s 180o from the sun in ecliptic longitude. The moon turns full on May 10 at 21:42 UTC, which at North American time zones translates to 6:42 p.m. ADT, 5:42 p.m. EDT, 4:42 p.m. CDT, 3:42 p.m. MDT and 2:42 p.m. PDT.

For North America, the moon will turn exactly full when the sun is above the horizon and the moon is still below it.

Because the moon stays more or less opposite the sun in our sky at the vicinity of full moon, tonight’s moon will rise in the east around sunset and climb highest up for the night around midnight (midway between sunset and sunrise). That’s true as seen from around the globe.

Then, around sunrise on May 11 – as seen from around the world – the moon will set in the west.

Worldwide map via Earthview, showing the day and night sides of Earth at the instant of the May full Moon (2017 May 10 at 21:42 UTC).

Bottom line: The moon is full on May 10, 2017. It swings a whopping 5o (10 moon diameters) north of the plane of Earth’s orbit around the sun and misses being in Earth’s shadow by a wide margin.

Read more: Total solar eclipse of August 21, 2017

Bruce McClure

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