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What’s special about a full moon?

You know it when you see it, but what makes a full moon full?

July 2016 full moon on the morning of July 19. Photo via EarthSky Facebook friend Kristal Alaimo-Moritz? at Sepulveda Basin Wildlife Reserve, Van Nuys, California.

July, 2016 full moon on the morning of July 19. Photo via EarthSky Facebook friend Kristal Alaimo-Moritz at Sepulveda Basin Wildlife Reserve, Van Nuys, California.

Full moon today. This full moon comes on July 19, 2016 at 2257 UTC (5:57 p.m. CDT; translate to your timezone).

What’s special about a full moon? Why does it tug our heartstrings? And why does a full moon look full, in contrast to other phases of the moon?

You’ll have to answer the first two questions for yourself, but here’s the answer to the third. At full moon, we’re seeing all of the moon’s day side.

At full moon, the moon and sun are on a line, with Earth in between. It’s as though Earth is the fulcrum of a seesaw, and the moon and sun are sitting on either end of the seesaw.

So as the sun sets in the west, the full moon rises. When the sun is below our feet at midnight, the full moon is highest in the sky. When the sun rises again at dawn, the full moon is setting. We all love line-ups of things in the heavens. Could it be the alignment of the sun, Earth and moon that causes us to feel a special connection with the full moon?

A full moon rises at sunset. But a nearly full moon - say, one day before full moon - can be seen ascending in the east in evening twilight. Beautiful!  Photo taken June 18, 2016 by Suzanne Murphy in Wisconsin.

A full moon rises at sunset. A day or two before full moon, you might catch sight of the moon ascending in the east in evening twilight. Beautiful! Photo taken June 18, 2016 by Suzanne Murphy in Wisconsin.

If there’s a lunar eclipse, it must happen at full moon. It’s only at the full moon phase that Earth’s shadow, extending opposite the sun, can fall on the moon’s face.

In many ways, a full moon is the opposite of a new moon. At both the new and full phases, the moon is on a line with the Earth and sun. At new moon, the moon is in the middle position along the line. At full moon, Earth is in the middle.

Full moon always comes about two weeks after new moon, when the moon is midway around in its orbit of Earth, as measured from one new moon to the next.

For a day or so around the crest of the moon's full phase, the moon looks full. July 21, 2016 photo by C.B. Devgun in New Delhi, India.

For a day or so around the crest of the moon’s full phase, the moon looks full. July 21, 2016 photo by C.B. Devgun in New Delhi, India.

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

Moon in 2016: Phases, cycles, eclipses, supermoons and more

Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side.

Each full moon has its own name. Here are the names of all the full moons

Deborah Byrd

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