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  • A Summer of Super Moons presented by Science@NASA

  • In June of last year, a full Moon made headlines.

  • The news media called it a "supermoon" because it was 14% bigger and 30% brighter than other full Moons of 2013.

  • Around the world, people went outside to marvel at its luminosity.

  • If you thought one supermoon was bright, how about three....?

  • The full Moons of summer 2014, July 12th, August 10th and Sept 9th will all be supermoons.

  • The scientific term for the phenomenon is 'perigee moon.'

  • Full Moons vary in size because of the oval shape of the Moon's orbit.

  • The Moon follows an elliptical path around Earth with one side ('perigee') about 50,000 km closer than the other ('apogee').

  • Full Moons that occur on the perigee side of the Moon's orbit seem extra big and bright.

  • This coincidence happens three times in 2014.

  • On July 12th and Sept 9th, the Moon becomes full on the same day as perigee.

  • On August 10th it becomes full during the same hour as perigee arguably making it an extra-super Moon.

  • It might seem that such a sequence must be rare.

  • Not so, says Geoff Chester of the US Naval Observatory.

  • Generally speaking, full Moons occur near perigee every 13 months and 18 days, so it's not all that unusual,” he says.

  • In fact, just last year there were three perigee Moons in a row, but only one was widely reported.”

  • In practice, it's not always easy to tell the difference between a supermoon and an ordinary full Moon.

  • A 30% difference in brightness can easily be masked by clouds and haze.

  • Also, there are no rulers floating in the sky to measure lunar diameters.

  • Hanging high overhead with no reference points to provide a sense of scale, one full Moon looks about the same size as any other.

  • Chester expects most reports of giant Moons this summer to be ...

  • illusory.

  • ''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 says.

  • The illusion occurs when the Moon is near the horizon.

  • For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects.

  • When the Moon illusion amplifies a perigee Moon, the swollen orb rising in the east at sunset can seem 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," says Chester.

  • "There's a part of me that wishes that this 'super-Moon' moniker would just dry up and blow away, like the term '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."

  • Indeed it is.

  • Mark your calendar July 12th, August 10th, and Sept 9th and enjoy the super-moonlight !

  • For more news about big bright things in the night sky, visit science. nasa. gov.

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ScienceCasts: A Summer of Super Moons

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    Halu Hsieh posted on 2014/09/09
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