Get ready for Saturday's 'Supermoon' with some facts from OMSI - KPTV - FOX 12

Get ready for Saturday's 'Supermoon' with some facts from OMSI

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Get ready, skywatchers. A "supermoon" is coinciding with Cinco de Mayo this year.

Due to the moon's position in the sky, its relationship to the Earth and the fact that it occurs during a full moon, what you'll see on the night of May 5 is what some are referring to as  a "supermoon."

It's happening at 8:35 p.m. on Saturday. Here's all you need to know, courtesy of OMSI Planetarium Manager Jim Todd.

  • As temperatures warm and the ground thaws, flowers are abundant and in bloom by this time. Thus, May's moon is called the Flower Moon; but it can also be called the Corn-Planting or Milk Moon. When we look at the full moon on Saturday, it will be just 221,705 miles away making it the Moon's closest approach to Earth in 2012.


  • Full moons vary in size because of the elliptical (oval) shape of the Moon's orbit. Perigee, or the Moon's closest approach Moon to Earth is about 31,068 miles closer to Earth than the its apogee or farthest distance. The Moon's distance at perigee changes by 3% over a period of 18.6 years, but in general while at perigee, a full moon would appear about 14% bigger and 30% brighter than a corresponding full moon at apogee, but it's not really all that much more dramatic than a regular full moon.


  • In March 2011, the full moon was less than one hour away from perigee--a near-perfect coincidence that happens about every 18.6 years.  On 2012 May 5, the full moon will occur within a minute of reaching actual perigee position (perigee at 8:34 p.m. PDT, and the full Moon at 8:35 p.m. PDT), but the actual perigee this month will be just a bit farther than the one of last year. 


  • According to the NASA JPL Solar Systems Dynamics (Horizons) computer, the "super-Moon" of 2011 March 19 was a tiny bit bigger than the "super-Moon" of 2012 May 5/6:
    2012-May-06 angular diameter: 2008" (= 0.5577 degree)
    2011-Mar-19 angular diameter: 2010" (= 0.5583 degree)


  • Before 2011, the comparable biggest/closest full Moon was March of 1993, and presumably the next comparably large full Moon will be 18.6 years from then sometime in late 2029.


  • Many are calling this full moon the "Supermoon," blaming it for dramatic land and ocean tides which trigger earthquakes. The tides are greatest during full and new moons, when the sun and moon are aligned either on the same or opposite sides of the Earth.  A very small correlation exists between full or new moons and seismic activity, because the stronger tidal forces caused by the alignment of the sun and moon puts added stress on tectonic plates. However, seismologists have found no evidence connecting lunar perigees to heightened seismic activity. Instead, the Earth constantly stores up energy and releases it any time the built-up energy becomes too great.

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