Get Ready For A Summer Of Supermoons
April Flowers for redOrbit.com – Your Universe Online
So-called supermoons are not a new phenomenon. However, the supermoon of July 2013 made headlines around the world, prompting a multitude of people to get out under the night sky to see it. The supermoon is approximately 14 percent larger and 30 percent brighter than a “regular” full moon.
If the one supermoon of last summer caused such a stir, what will the three this summer cause? All three full moons this summer — July 12, August 10, and September 9 — will be supermoons.
Though “supermoon” is a great media term to get people excited, the scientific name for such a moon is “perigee moon.” The Moon’s orbit around Earth is elliptical, which makes the size of the full moon one month different from the size the next month. Along this orbit are points known as perigee and apogee. At perigee, the Moon is at its closest point to Earth, approximately 31,000 miles closer than when it is at apogee.
[ Watch the Video: ScienceCasts: A Summer Of Super Moons ]
Moon Connection reports that it would be difficult to determine the difference without something to compare the moon to, but pictures of the moon at both locations make the difference obvious. Perigee moons appear much brighter and larger than at any other point along the orbit. Telling the difference in brightness is not always easy either. Clouds or haze can mask the extra luminosity.
Twice this summer the Moon will become full during the day of perigee (July 12 and September 9). The August 10 Moon, however, becomes full during the same hour of perigee – perhaps making this an extraordinary supermoon.
Geoff Chester of the US Naval Observatory notes that, despite media coverage, this is not such a rare occurrence after all.
“Generally speaking, full Moons occur near perigee every 13 months and 18 days, so it’s not all that unusual,” he said. “In fact, just last year there were three perigee Moons in a row, but only one was widely reported.”
In fact, redOrbit reported that there were two supermoons this past January.
Chester believes that most reports of giant Moons this summer will be caused by an effect named the Moon Illusion.
“The ‘Moon Illusion’ is probably what will make people remember this coming set of Full Moons, more than the actual view of the Moon itself,” he said.
The Moon Illusion effect is seen when the Moon is near the horizon. Low-hanging moons seem to appear unnaturally large beaming through trees, buildings and other objects — an effect not fully understood by astronomers or psychologists. Add the Moon Illusion to a perigee moon and the seemingly swollen orb rising at sunset can appear very super indeed.
“I guarantee that some folks will think it’s the biggest Moon they’ve ever seen if they catch it rising over a distant horizon, because the media will have told them to pay attention to this particular one,” Chester told Science@NASA’s Dr. Tony Phillips.
“There’s a part of me that wishes that this ‘super-Moon’ moniker would just dry up and blow away, like the ‘Blood-Moon’ that accompanied the most recent lunar eclipse, because it tends to promulgate a lot of mis-information,” admits Chester. “However, if it gets people out and looking at the night sky and maybe hooks them into astronomy, then it’s a good thing.”
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