Tuesday, September 9, 2014

Harvest Moon

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

~By Nora Bayes and Jack Norworth (1903)

The Harvest Moon is the full moon closest to the autumnal equinox.  In the Northern Hemisphere, the 2014 autumnal equinox comes on September 23, so the September 8-9 full moon counts as the Northern Hemisphere’s Harvest Moon.

Along ocean coastlines this full moon will to bring along wide-ranging spring tides for several days following full moon. High tides will climb higher than usual and the low tides will fall lower than usual.

 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 to 35 minutes later daily for several days before and after the full Harvest moon because the ecliptic – 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.  After the full Harvest Moon, you’ll see the moon ascending in the east relatively soon after sunset for a few days in a row at northerly latitudes. Because of this, it seems as if there are several full moons – for a few nights in a row – around the time of the Harvest Moon. The shorter-than-usual time between moonrises around the full Harvest Moon means no long period of darkness between sunset and moonrise for days in succession. The light of the Harvest Moon helped farmers to gather their crops, despite the diminishing daylight hours. As the sun’s light faded in the west, the moon would soon rise in the east to illuminate the fields throughout the night.

in 2014, the Harvest Moon comes one month after the year’s closest and largest full moon on August 10, 2014. So this year’s Harvest Moon counts as a supermoon.  A moon is a supermoon when it’s full and makes it closest approach to Earth in its orbit.

The orange color of a moon near the horizon 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 sky above looks blue because the atmosphere scatters blue light. 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.

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