Archive | September 22, 2012

Harvest Moon

Image Credit: Dan Bush of Missouri Skies

Shine on, shine on harvest moon

Up in the sky,

I ain’t had no lovin’ Since January, February, June or July

Snow time ain’t no time to stay Outdoors and spoon,

So shine on, shine on harvest moon,

For me and my gal

~ Shine On Harvest Moon By Nora Bayes and Jack Norworth (1903)

Traditionally in skylore, the Harvest Moon is the full moon closest to the autumnal equinox. In 2012, for us in the Northern Hemisphere, the autumnal equinox comes on September 22. The full moon for us in the U.S. will come on the night of September 29. That makes the September 29-30 full moon the Harvest Moon

Harvest Moon is just a name.  It’s the name for the full moon nearest the autumnal equinox. In the Northern Hemisphere, you’ll always see the Harvest Moon in either September or October.  In the Southern Hemisphere, a moon with these same characteristics always comes in March or April.

But the Harvest Moon is more.  Nature is particularly cooperative around the time of the autumn equinox to make the full moonrises unique around this time.

Here’s what happens.  On average, the moon rises about 50 minutes later each day.  But when a full moon happens close to the autumnal equinox, the moon (at mid-temperate latitudes) rises only about 30 minutes later daily for several days before and after the full Harvest moon.  Why?  The reason is that the ecliptic– or the moon’s orbital path – makes a narrow angle with the evening horizon around the time of the autumn equinox.  The narrow angle of the ecliptic results in a shorter-than-usual rising time between successive moonrises around the full Harvest Moon.the actual size of the Harvest Moon depends on the year.  The Harvest Moon has the reputation of being especially big and bright and orange.  But it isn’t really the Harvest Moon’s size or brightness that distinguishes it from other full moons.  In fact, the 2012 Harvest Moon is a touch smaller than an average-sized full moon.

Still, you might think otherwise.  That’s because the Harvest Moon has such a powerful mystique.  Many people look for it shortly after sunset around the time of full moon.  After sunset around any full moon, the moon will always be near the horizon.  It’ll just have risen.  It’s the location of the moon near the horizon that causes the Harvest Moon – or any full moon – to look big and orange in color.  

The orange color of a moon near the horizon is a true physical effect.  It stems from the fact that – when you look toward the horizon – you are looking through a greater thickness of Earth’s atmosphere than when you gaze up and overhead.  The atmosphere scatters blue light – that’s why the sky looks blue.  The greater thickness of atmosphere in the direction of a horizon scatters blue light most effectively, but it lets red light pass through to your eyes.  So a moon near the horizon takes on a yellow or orange or reddish hue.

 

Photo Credit: Harvest Moon By Dan Bush-

Excerpts From: earthsky.com

http://earthsky.org/astronomy-essentials/harvest-moon-2