ORLANDO, Fla. – The Harvest Moon has been shining bright between thick clouds the last few nights, but it doesn’t happen in the same month every year.
This moon usually happens in September, but unlike most, it’s not dedicated to the month of September. Sometimes it happens in October.
Why? It has everything to do with when the autumnal equinox occurs. This particular moon occurs closest to fall. It’s when the lunar cycle and the Gregorian calendar line up.
Wait, there’s more.
Typically, the moon will rise later and later each night by almost an hour based on its orbit and the Earth’s orbit around the sun and its rotation.
The moon takes 27 days to complete a full circle, resulting in a 12-13 degree shift to the east daily. As a result of this shift, the Earth has to rotate a bit longer each day to bring the moon into view.
During the Harvest Moon, the moon rises at sunset for a few days, making it seem like there’s a full moon rising for more than one night. This is due to the shallow angle along our horizon this time of year.
For the last three days, the average moon rise time is about 20-30 minutes later, instead of almost an hour. Depending on location, this time can be even less. For example, Europe would only see a 20-minute delay in the moon rise time, compared to the 25-minute delay the United States experiences. After the three day period, the normal hour-long delay returns.
Why is it called the Harvest Moon?
Think back to when farmers relied on the sun for light to work. This moon provided a lot more light during the few nights it seems to rise around the same time. This was a big help to farmers harvesting the crops grown all summer long. It gave them extra time to work in the fields. If the autumnal equinox falls in October, this is no longer the Harvest Moon, but takes the name of Hunter’s Moon.