Shine on, shine on Harvest Moon, up in the sky… The Harvest Moon is the full moon that occurs the closest to the autumnal equinox. In 2017, the equinox falls almost exactly halfway between two full moons. The full moon on October 5 is officially the Harvest Moon, because it is slightly closer to the equinox on September 22 than the full moon of September 5-6.
However, in most respects, the September 2017 and October 2017 full moons can be regarded as Harvest Moon co-stars. By that we mean that both have the characteristics of a Harvest Moon. The primary Harvest Moon characteristic has to do with the moonrise. On the average, the moon rises some 50 minutes later with each passing day. Around the time of the full Harvest Moon, the lag time between successive moonrises is reduced to a yearly low.
In 2017, there’s no appreciable difference between the lag in moonrise times associated with September and October full moons. In both of these months, the moon rises a shorter-than-usual time after sunset for several evenings in a row, following the date of full moon.
There's a detailed explanation of why there's a difference in the lag in moonrise times, and how it makes the Harvest Moon seem bigger and brighter. I read it and thought, "But that's only in the Northern Hemisphere!" Well, duh. In the Southern Hemisphere, autumn, and the Harvest Moon, comes in March or April. Read more about what makes a Harvest Moon special, and why you should enjoy it in both September and October this year. -Thanks, Walter!
(Image credit: Roadcrusher)