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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?

Last year's June full moon by Anthony Lynch Photography in Dublin, Ireland.

Last year’s June full moon by Anthony Lynch Photography in Dublin, Ireland.

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?

Next full moon comes June 20, 2016, at 1102 UTC (6:02 a.m. CDT; translate to your timezone), same day as the upcoming June solstice.

Read more: June solstice full moon in 2016

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. Photo taken February 24, 2013 by EarthSky Facebook friend Jorgen Norrland Andersson in Sweden. Thank you, Jorgen!

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

Understanding Moon Phases
Waxing Crescent
First Quarter
Waxing Gibbous
Full Moon
Waning Gibbous
Last Quarter
Waning Crescent
New Moon

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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