Rare harvest moon on Friday the 13th has skywatchers excited about the once-in-20-years occurrence

It's rare for the whole of the US to experience a full moon on Friday the 13th. The last time this happened was on October 13, 2000, and the next will be in August 2049


                            Rare harvest moon on Friday the 13th has skywatchers excited about the once-in-20-years occurrence

Grab your binoculars and head outside!

Skywatchers are in for a spectacular show: a full harvest moon will make a rare appearance in the night sky in some parts of the US on Friday, the 13th. 

A full moon occurs when the side of the moon that faces the Earth is fully lit up by the sun. But not all full moons look the same. The term "harvest moon" refers to the full, bright moon that occurs closest to the start of autumn.

The name goes back to the time before electricity when farmers depended on the moon's light to harvest their crops late into the night. The moon's light was particularly important during fall when harvests are the largest.

The arrival of the Harvest Moon this year will depend on which time zone you happen to live in. "September's full Moon is coming up, the so-called 'Harvest Moon', which is the full moon nearest to the autumnal equinox (September 23)," stated a report in Farmers' Almanac, an annual North American periodical, which has been in publication since 1818.

"If you live in the Eastern Time Zone, the moment the moon turns full will occur just after midnight — at 12.33 am on Saturday, the 14th. But if you live elsewhere in the country — in the Central, Mountain, or Pacific time zones — the moment that the moon turns full comes before midnight on Friday, the 13th," the report said.

It added, "It has been calculated that to have a full moon occur on the 13th day of a particular month, and for that day to be a Friday, it is (on average) a once-in-20-year occurrence."

The name harvest moon goes back to the time before electricity when farmers depended on the moon's light to harvest their crops late into the night (Getty Images)

Friday the 13th is probably a spooky day for some superstitious people, as is a full moon. However, what is actually rare is a nationwide Friday the 13th full moon. The last time this happened was on October 13, 2000, and the next one will not appear until August 2049.

What makes the harvest moon unique is that while on average, the moon rises about 50 minutes later each day, at this time of year, the moon seems to rise at nearly the same time each night, leading up to when it is full. The interval between sunsets and when the moon rises reduces to approximately 27 minutes on average. 

"What sets this upcoming full moon apart from the others is that farmers, at the peak of the current harvest season, can work late into the night by this moon's light. For example, between September 12 and 14, the rising of the moon comes, on average, less than 27 minutes later each night, thus providing light for the farmer to continue gathering crops, even after the sun has set," shared the Farmers' Almanac.

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