Sky-watchers gazing at the full moon rising on the evening of Sunday, August 10, will be treated to the largest and brightest full moon of the year—also known as an extra-supermoon.
This lunar show will be the second act in a trio of supermoons that are gracing our skies this summer.
Thanks to coincidental timing of the moon being at its closest approach to Earth for 2014, at 221,765 miles (356,896 kilometers) away, while in its full phase this week our planet’s companion will appear 16 percent larger and 30 percent brighter than usual.
While some are calling it a supermoon, the astronomical community prefers to use the term “perigee full moon,” and point out that they are not all that rare since the alignment between a full moon phase with perigee occurs every year.
In 2014 there are three supermoons—on July 12, August 10, and September 9, when the moon becomes full on the same day as perigee.
The monthly full moon always looks like a big disk, but because its orbit is egg-shaped around the Earth, there are times when the moon is at what astronomers call perigee—its shortest distance from Earth in the roughly month-long lunar cycle—or it can be at apogee, its farthest distance from Earth.
Likewise, because the size of the moon’s orbit varies slightly, each monthly perigee is not always the same distance away from Earth.
How Rare Is This Event?
But this weekend the timing couldn’t be more perfect, with perigee occurring only 26 minutes before the moon officially reaches its full phase at 18:10 Universal Time (UT) (2:10 p.m. EDT) on August 10. By the way, the moon will be straight overhead in the sky above the Indian Ocean at that specific time.
Such tight timing won’t occur again until 2034.
While this neat convergence will make this an extra-supermoon, don’t be surprised if you can’t spot the difference from other full moons you might have gazed at in past months. After all, the difference in distance between Earth and the moon from last month’s supermoon will be no more than a few hundred miles or kilometers—something the human eye really can’t detect.
In March 2011 a so-called supermoon was at its closest in two decades at only 221,565 miles (356,575 kilometers).
Best Time to Head Outside?
But there is no doubt that folks everywhere looking up this weekend at the full moon will find it impressive, especially as it rises into the sky.
For moon-watchers and photo hounds, the best time to catch all the action is just after your local sunset on Sunday, just as the full moon begins to rise.
As the silvery orb creeps above your local horizon, the most picturesque moments will present themselves. While still at low altitude, the moon will make for a particularly pretty shot as it poses with foreground objects like mountains and trees.
An optical illusion known as “the Moon Illusion” makes the moon appear larger near the horizon: Because of the Ponzo effect, our brain is tricked into thinking the lunar disk is larger than it is.
Try using tripods and remote timers to stabilize your shots. Also, a telephoto lens (200 mm and up) will allow you to zoom in on the lunar disk while getting a distant foreground object to appear larger in the same frame.
And if you miss this week’s lunacy, remember to mark your calendar for September 9, for your next chance to catch the so-called supermoon.