In many cultures, September's full moon is associated with the harvest. Songs have been written about it, video games have rendered it, and literature has romanticized it; the cultural importance of the harvest moon goes without saying, but do you know the historical significance of the harvest moon? Gardeners can surmise that the harvest moon coincides with the time of year when much of the Northern Hemisphere begins to harvest their summer's bounty - which is true! There is a little more to the harvest moon than a signifier of the season's end, though.
Throughout the year, the moon rises an average of about 50 minutes later each day; however, for a few nights around the harvest moon, the moon rises at nearly the same time, around sunset. It rises about 25 to 30 minutes later across the northern US, and about 10 to 20 minutes later farther north in Canada and Europe.
Before modern farming techniques, the harvest moon was an incredibly significant event. It allowed farmers to utilize the extra light that the full moon provided after sunset to extend their harvest for a few days. This made it possible to gather as many crops as they could before autumn, and eventually, winter, would set in.
Want to know the science behind this phenomenon? Here's the astronomical explanation of this event:
When paired with the larger orbit of the Earth around the Sun, the moon's orbital motion carries it farther eastward from night to night. On any given moonrise, the moon occupies a specific place in the sky, but when the Earth rotates towards that point 24 hours later, the moon has shifted about 12 degrees, taking the Earth about 50 minutes longer to rotate towards the moon--thus, the moonrise spectacle!
Why then is September's moon (the moon closest to the autumnal equinox) more consistent than others? With the axial rotation of the Earth and the simultaneous tilting of the planet that brings about our seasonal changes, the moon's orbit on successive nights in late summer is nearly parallel to the horizon at that time, and the Earth does not have to turn as far to bring up the moon. This is more noticeable further north, and less noticeable further south. This makes sense when learning that the term "harvest moon" was first coined by Northern Europeans.
The harvest moon has cultural implications in Eastern cultures, too. The Mid-Autumn Festival in China occurs around the harvest moon and is celebrated by baking and eating mooncakes, lighting lanterns as symbolic beacons that light people's path to prosperity and good fortune, and gathering together to celebrate the harvest of summer.
People have long used the moon as a planting guide, and to this day we still recognize the changing of seasons and the timing of the months by our lunar guide. We hope this harvest moon brings bountiful harvests of summer's endeavors and bright moonbeams as summer turns to fall and day turns to night.