It’s a weekend full of lunacy. The impending full moon, coinciding with the moon’s closest approach to Earth in its orbit, has become known as the “super moon.” In proper astronomical terms, this coupling is referred to as the perigee full moon.
Our lunar companion travels in an elliptical orbit, which means that for every lunar cycle, it snuggles in to a position nearest Earth- its perigee, and strays to a position farthest away – its apogee.
When the moon’s full phase coincides with perigee, the ‘super moon’ moniker is invoked.
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The full perigee or ‘super moon’ appears about 14 percent larger and 30 percent brighter than the more distant apogee full moon.
Matter of minutes: The upcoming perigee occurs within minutes of the official full moon (but after the moon will have set for the day and not visible in that particular time window). Make some toast and pour your coffee, since on Sunday, June 23 perigee is at 7:11 a.m. eastern, when the Earth and moon will be about 356,991 kilometers, or 221,894 miles apart, according to the Royal Astronomical Society of Canada. A mere 22 minutes later – at 7:33 a.m. – the moon becomes full, according to the U.S. Naval Observatory.
Since the coincidence of perigee and full moon falls on Sunday morning, the plump moon on Saturday and Sunday night will be each a sight to behold.
Saturday night, June 22: The moon rises at 7:50 p.m. (yes, it is still daylight) in the southeastern sky. About 99 percent of the waxing gibbous moon’s visible disk is illuminated, according to the Naval Observatory. And at -12 magnitude, it is very bright and you can’t miss it. This moon is due south at 12:53 a.m. eastern on Sunday morning and it sets at 5:58 a.m. in the southwest. (Compare the moon’s brilliance to Venus, low in the northwestern sky at dusk is -3.9 magnitude, very bright, much like a distant airliner on approach to Washington Dulles Airport.)
Sunday night, June 23: Moonrise occurs at 8:48 p.m. eastern in the southeast and the lunar disk remains magnificently bright at -12 magnitude.
On either Saturday or Sunday, if you catch the moon rising as it ascends the horizon, it may look gigantic. Sure, the moon appears slightly larger than your average full moon, but you’ll still be experiencing the moon illusion.
Astronomer Sten Odenwald offers an explanation on his Astronomy Café website. Earthly objects, such as trees or houses or mountains give the moon context. As the moon reaches toward the heavens, the moon appears smaller, but in reality it is the same size as minutes or hours before.
He says our brains and eyes fall victim to illusion: “It has to do with how our brain uses information in the eye’s visual field for finding clues about the sizes of things it is seeing.”
As mentioned earlier, the moon can be close … and far away. Our little orb reaches apogee – the most distance between the new moon and earth on July 6 at 8:36 p.m. eastern (July 7 at 12:36 a.m. UT). At 406,493 kilometers (252,583 miles) it is also the most-distant moon of the year.
To provide ample time for party planning, the full perigee or ‘super moon’ next returns Aug. 10, 2014 – just in time to wash out some of next year’s Perseid meteors.
Supermoon 2012: Reactions and photos (May 2012)
Super Moon over Washington, D.C. (March 2011)