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Super Moon: Saturday, May 5 At Midnight Eastern Time Should Offer Peak Viewing

Posted: 05/04/2012 8:48 am Updated: 05/04/2012 2:43 pm

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By: Joe Rao
Published: 05/04/2012 06:48 AM EDT on SPACE.com

On Saturday (May 5) at 11:35 p.m. EDT, the moon will officially turn full. And only 25 minutes later the moon will also arrive at perigee, its closest approach to Earth — a distance of 221,802 miles (356,955 kilometers) away. 

The effect of this coincidence is a stunning skywatching sight called the "supermoon."

In fact, this month's perigee is the closest of any perigee in 2012 (they vary by about 3 percent, because the moon's orbit is not perfectly circular). The result will be a 16 percent brighter-than-average full moon accompanied by unusually high and low tides this weekend and into the new week.

In contrast, later this year, on Nov. 28, the full moon will closely coincide with apogee, the moon's farthest point from Earth. [Amazing Supermoon Photos from 2011]

Spring tides

Every month, "spring" tides occur when the moon is full and new. The word "spring," in this case, is derived from the German springen, to "spring up," and is not — as is often mistaken — a reference to the spring season. At these times the moon and sun form a line with Earth, so their tidal effects add together.  The sun, because of its distance, exerts a little less than half the tidal force of the moon.

"Neap" tides, on the other hand, occur at those times when the moon is at first and last quarter and work at cross-purposes with the sun. At these times, tides are weak.

Tidal force varies as the inverse cube of an object's distance. During the supermoon on Saturday, the moon will be 12.2 percent closer at perigee than it will be two weeks later at apogee, which will nearly coincide with a new moon.  Therefore it will exert 42 percent more tidal force during this weekend's spring tides than during the spring tides near apogee two weeks later.  

Although a full moon theoretically lasts just a moment, that moment is imperceptible to ordinary observation, and for a day or so before and after most will speak of seeing the nearly full moon as "full." The shaded strip is so narrow, and changing in apparent width so slowly, that it is hard for the naked eye to tell whether it is present or on which side it is. 

And while this weekend's moon will be — as the Observer's Handbook of the Royal Astronomical Society of Canada suggests on page 101 —- the "largest full moon of 2012," the variation of the moon's distance is not readily apparent to observers viewing the moon directly. 

Or is it?

Moon illusion

When the perigee moon lies close to the horizon it can appear absolutely enormous. That is when the famous "moon illusion" combines with reality to produce a truly stunning view.

For reasons not fully understood by astronomers or psychologists, a low-hanging moon looks incredibly large when hovering near to trees, buildings and other foreground objects. The fact that the moon will be much closer than usual this weekend will only serve to amplify this strange effect.

So, a perigee moon, either rising in the East at sunset or dropping down in the West at sunrise might seem to make the moon appear so close that it almost seems that you could touch it. You can check out this effect for yourself by first noting the times for moonrise and moonset in your area here: http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-year-us

And one final note: Saturday also marks the midpoint of spring in the Northern Hemisphere. The exact moment between the March equinox and the June solstice occurs at 10:11 a.m. EDT May 5.  And this spring's big full moon seemingly places an exclamation point on this seasonal benchmark. Traditionally, the full moon of May is known as the "Flower Moon" since flowers are now abundant most everywhere. It is also known as the Full Corn Planting Moon or the Milk Moon.

Happy moon watching!

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

Copyright 2012 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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  • A perigee moon rises above the Almudena

    A perigee moon rises above the Almudena Cathedral in Madrid on March 19, 2011. A perigee moon is visible when the moon's orbit position is at its closest point to Earth during a full moon phase. AFP PHOTOAFP PHOTO/ Pedro ARMESTRE (Photo credit should read PEDRO ARMESTRE/AFP/Getty Images)

  • Biggest Moon In Almost 20 Years Rises In DC

    WASHINGTON - MARCH 19: In this handout photo provided by NASA, the full moon is seen as it rises near the Lincoln Memorial, March 19, 201, in Washington, DC. The full moon tonight is called a 'Super Perigee Moon' since it is at it's closest to Earth in 2011. The last full moon so big and close to Earth occurred in March of 1993. (Photo by Bill Ingalls/NASA via Getty Images)

  • A perigee moon rises next to the Nationa

    A perigee moon rises next to the National Monument and the Capitol Hill in Washington, DC, on March 19, 2011. A perigee moon is visible when the moon's orbit position is at its closest point to Earth during a full moon phase. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

  • A perigee moon rises in Washington, DC,

    A perigee moon rises in Washington, DC, on March 19, 2011. A perigee moon is visible when the moon's orbit position is at its closest point to Earth during a full moon phase. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO / Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

  • The full moon rises behind the statue of

    The full moon rises behind the statue of Mahathma Gandhi in Hyderabad on March 19, 2011. Full Moons vary in size because of the oval shape of the Moon's orbit. It is an ellipse with one side (perigee) about 50,000 km closer to Earth than the other (apogee). Nearby perigee moons are about 14 percent bigger and 30 percent brighter than lesser moons that occur on the apogee side of the Moon's orbit. According to US Naval Observatory in Washington, D.C. 'The full Moon of March 19 occurs less than one hour away from perigeea near-perfect coincidence that happens only 18 years or so'. AFP PHOTO/Noah SEELAM (Photo credit should read NOAH SEELAM/AFP/Getty Images)

  • The full moon is seen behind a bronze st

    The full moon is seen behind a bronze statue standing on the left bank of Vltava river on Mala Strana Prague's quarter early on March 20, 2011. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO / MICHAL CIZEK (Photo credit should read MICHAL CIZEK/AFP/Getty Images)

  • The full moon rises over rooftops March

    The full moon rises over rooftops March 19, 2011 in this view from the east side of Manhattan in New York. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO / Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images)

  • A March 20, 2011 photo taken at approxim

    A March 20, 2011 photo taken at approximately 0457 GMT shows the moon seen from Chevy Chase, Maryland. The moon is in its closest orbit to Earth, at 356,577 Kms away, the closest in 18 years. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)

  • The statue of freedom, ontop of the US C

    The statue of freedom, ontop of the US Capitol Hill is pictured against a perigee moon as it rises in Washington, DC, on March 19, 2011. A perigee moon is visible when the moon's orbit position is at its closest point to Earth during a full moon phase. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO/Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

  • A perigee moon rises in Washington, DC,

    A perigee moon rises in Washington, DC, on March 19, 2011. A perigee moon is visible when the moon's orbit position is at its closest point to Earth during a full moon phase. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO/Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/Getty Images)

  • The full moon rises March 19, 2011 in th

    The full moon rises March 19, 2011 in this view from the east side of Manhattan in New York. The full moon coincided with its closest approach to the Earth, 221,565 miles (356,575 km), making the so-called 'super moon' look slightly larger than average. AFP PHOTO/Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images)

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