Lunar light

A sliver of moon seen over Mansfield glows golden on a late summer evening. The moon will be full just after midnight on Friday the 13th.

September’s full moon is coming up — the so-called “Harvest Moon,” which is the full moon nearest to the autumnal equinox (Sept. 23). The arrival of this year’s Harvest Moon will depend on which time zone you happen to live in.

If you live in the Eastern time zone, the moment the moon turns full will occur just after midnight, at 12:33 a.m. on Saturday the 14th. But for those in the Central, Mountain, or Pacific time zones, the moment that the Moon turns full comes before midnight on Friday the 13th.

Interestingly, the last time this happened — June 13, 2014 — it was the reverse of what will happen this month. Nationwide, we haven’t had a Friday the 13th full moon since Oct. 13, 2000, and it won’t happen again until Aug. 13, 2049.

What sets this upcoming full moon apart from the others is that, traditionally, farmers at the peak of the current harvest season could work late into the night by this moon’s light. The moon rises about the time the sun sets, but more importantly at this time of year, instead of rising its normal average 50 minutes later each day, the moon seems to rise at nearly the same time each night leading up to when it’s full.

For example, between Sept. 12 and 14, the rising of the moon comes on average less than 27 minutes later each night, providing light for farmers to continue gathering crops even after the sun has set.

The reason for this seasonal circumstance is that at this time of the year, the path of the moon through the sky is as close to being along the horizon as it can get. Thus, from night to night the moon moves more horizontally than vertically, and rises sooner from one night to the next.

Micro moon?

To add to this full moon madness, this upcoming full moon very nearly coincides with apogee — that point in its orbit which places it at its greatest distance from the Earth: 252,100 miles away.

Last February, when the full Moon coincided with perigee, its closest point to Earth, it was more than 30,000 miles closer and was accordingly branded a “supermoon.”

But this month’s full moon will appear about 14 percent smaller, leading some to call it a “micro” moon.

Some will claim that this year’s full Harvest Moon indeed appears to be smaller than usual. But the truth of the matter is that without knowing in advance whether a full moon of a given month might be branded either “super” or “micro,” the appearance of our natural satellite to most eyes really doesn’t look all that much different.

Here’s hoping for clear skies so you can get outside and enjoy it!

Joe Rao is a contributing astronomer for the Farmers’ Almanac: farmersalmanac.com.

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