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Saturday, November 12, 2016

Closest Perigee-Synergy Moon on November 14, 2016

Astronomy Club Meeting, Saturday, November 12
Please join the Davis Astronomy Club on Saturday, November 12 starting at 7:00pm at the Explorit Science Center (3141 5th Street, Davis) when we will discuss the November 14 supermoon in particular and our moon in general. Everyone is invited to the free meeting indoors, followed by a star party outdoors (weather permitting). 

Closest Perigee-Synergy Moon (Supermoon) on November 14, 2016
by Vinita Domier

On November 14 at 3:52am, just two hours before it is in full phase, our nearest celestial neighbor, the moon, will make its closest approach to Earth, resulting in a perigee-synergy moon, or supermoon. This phenomenon occurs when a new or full moon coincides with its shortest distance from Earth, resulting in the full moon appearing up to fourteen times bigger and hence thirty times brighter since it is up to 26,000 miles closer.

The November 14 supermoon is a very special one because the last time the full-phase supermoon was this close was on January 26, 1948, and the next closest supermoon will not occur until November 25, 2034. This supermoon is also part of the triad of supermoons this year, as it was preceded by one on October 16, and is going to be followed by another on December 12. Incidentally, the last total lunar eclipse visible in North America on September 27, 2015 was also a supermoon.

Like all celestial bodies, the moon’s (27.3-day sidereal period) orbital path around the Earth is elliptical in shape, with the Earth at one of the foci. This results in the moon’s distance varying between 225,804 miles at its closest approach known as perigee, to 251,968 miles at its farthest approach know as apogee, with the average distance of the moon from Earth being 238,800 miles.

The Earth and the moon together also orbit the sun resulting in the moon’s (29.5-day synodic period) phases cycle. Even though one half of the moon is always bathed in sunlight and the other half is always in shadow, from our earthly perspective we see varying degrees of the lit and dark parts of the moon. The orbital dance results in moon phases changing from new (when 0% of the lit side is visible), to quarter (when 50% of the lit side is visible), to full (when 100% of the lit side is visible), and back to quarter and new again. 

Two times in a 12-month period, during the moon-Earth system’s yearly orbital path around the sun, the three celestial bodies somewhat align. A perfect straight line alignment, known as synergy of the Earth-moon-sun system, results in an eclipse visible from Earth. A lunar eclipse will occur during a synergy if Earth is in a straight line between the sun and the full moon, resulting the moon being partially or totally obscured by the Earth’s shadow. A solar eclipse will occur during a synergy if the new moon is in a straight line between sun and Earth, resulting in the sun being partially or totally obscured by the moon’s shadow for Earth observers.

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 For more information, please contact Vinita Domier at

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