Home > Concepts, Observing, The Moon > Ephemeris: 09/08/2025 – Previewing the Harvest Moon Effect

Ephemeris: 09/08/2025 – Previewing the Harvest Moon Effect

September 8, 2025

This is Ephemeris for Monday, September 8th. Today the Sun will be up for 12 hours and 52 minutes, setting at 8:05, and it will rise tomorrow at 7:14. The Moon, 1 day past full, will rise at 8:30 this evening.

Last night’s full moon was not the Harvest Moon. We normally expect the Harvest Moon to come in September, but this year it does not because it is not the closest full moon to the autumnal equinox. The full moon of October 6th, this year, is the nearest full moon to the autumnal equinox. So it this month’s full moon is called the Corn Moon. But the effects of this full moon are the same as the Harvest Moon, in that the Moon rises only slightly later each evening for about a week or so. The Moon tonight will rise only 20 minutes later than it rose last night. The average day-to-day interval of moon rising is about 50 minutes. This earlier rising time had the effect of extending twilight which helped early farmers with an extra hour to gather in their crops.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum

The full moons of late summer and early autumn show the harvest moon effect. The Harvest Moon itself is the nearest full moon to the autumnal equinox. This year’s full moon in September is farther from the autumnal equinox than the full moon in October so it gets the name Corn Moon, however the effect is the same. The moon’s path in the sky near the eastern horizon when the Moon is full, this time of year, is very low to the horizon. This causes the Moon to rise much less than the 50 minutes average gain in rising times. The opposite is true for the late winter and early spring full moons which rise each night at a much greater interval than average. Created using Cartes du Ciel, (Sky Charts).
Categories: Concepts, Observing, The Moon Tags: ,