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Update on Lunar Info

You may have seen or heard about next week's full moon.  The message circulating is the first one below.  I was a bit suspicious so I sent it to Dr. Marston in our Astronomy department.   His response is the second message below.  NEVER TRUST THE INTERNET.

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This year will be the first full moon to occur on the winter solstice, Dec. 22, commonly called the first day of winter.  Since a full moon on the winter solstice occurred in conjunction with a lunar perigee (point in the moon's orbit that is closest to Earth) The moon will appear about 14% larger than it does at apogee (the point in it's elliptical orbit that is farthest from the Earth) since the Earth is also several million miles closer to the sun at this time of the year than in the summer, sunlight striking the moon is about 7% stronger making it brighter.  Also, this will be the closest perigee of the Moon of the year since the moon's orbit is constantly reforming.  If the weather is clear and there is a snow cover where you live (ha ha), it is believed that even car headlights will be superfluous.

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Information provided by Dr. Anthony Marston, Drake University.

Some of this is somewhat true. 
It is a full moon on 22 December and the Earth is closer to the Sun in the winter than in the summer, but not on 22 December -- more like early to mid-January.

The numbers appear well off.
First of all the variation in Earth Sun distance is of the order 1% in a given year (at 93 million miles this comes out to less than 1 million miles -- not the millions of miles quoted and overall 2% change in sunlight striking the Earth). Second, the Moon's orbit does not change by as much as 14% to give the 14% difference noted above. Half of that is closer to the mark -- and I'm being generous (this would be the approx. brightness increase seen as compared to an average full moon).

I think someone is exaggerating just a bit.

This is the second message like this that I have seen. The first one included predictions of tidal stresses causing earthquakes. This isn't going to happen.   ---------------------------


Thomas Rosburg
Dept. of Biology
Drake University
2507 University Ave.
Des Moines, Iowa  50311-4505

515-271-2920
thomas.rosburg@drake.edu


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