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Ephemeris: 09/08/2025 – Previewing the Harvest Moon Effect
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
Ephemeris: 08/20/2024 – The Moon will pass Saturn tonight
This is Ephemeris for Tuesday, August 20th. Today the Sun will be up for 13 hours and 47 minutes, setting at 8:39, and it will rise tomorrow at 6:52. The Moon, 1 day past full, will rise at 9:25 this evening.
The bright Moon tonight will have a companion. It will be the planet Saturn, which the Moon will pass below this evening. The Moon being very bright will make it difficult to spot Saturn. So it will seem that Saturn is moving above the Moon, not the other way around. It may take a pair of binoculars to spot Saturn because it will be less than the diameter of the Moon above and to the left of the Moon early in the evening. Moving to the upper right of the Moon towards midnight. Our next full moon will be the Harvest Moon. We’re already seeing the harvest moon effect, that is the Moon rises at nearly the same time on consecutive nights, or almost so. Tomorrow’s Moon will rise only 21 minutes later than tonight’s Moon, at much less than the 50 minutes per night average.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT–4 hours). Times will be different for other locations.
Addendum
Saturn will be occulted (covered up) by the Moon tonight for portions of the Earth
Ephemeris: 09/28/2023 – Tomorrow night’s full moon is the Harvest Moon
This is Ephemeris for Thursday, September 28th. Today the Sun will be up for 11 hours and 52 minutes, setting at 7:29, and it will rise tomorrow at 7:38. The Moon, 1 day before full, will set at 7:43 tomorrow morning.
Tomorrow night’s full moon is the Harvest Moon. It is the most famous of the named full moons, and was very useful in the days before electric lights. The reason is that the Moon, around the time it is full, doesn’t advance its rising time very much from night to night, effectively adding its light to twilight to allow more time to gather in crops. This is because the Moon is moving north as well as eastward. The farther north it is, the longer it stays up and retards the advance in rise times. On average, the Moon rises 50 minutes later each night. This week, the interval is down near 22 minutes advance in moonrise times per day, extending twilight and the amount of time each day to harvest the crops for a few more days.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT –4 hours). They may be different for your location.
Addendum
My interest in the Harvest Moon is not in harvesting the crops. I just have a little garden, so it doesn’t take that long to pick tomatoes or whatever. But as an amateur astronomer I’m more interested in deep sky objects than I am in planets. Deep sky objects or DSOs are objects beyond the solar system and are usually very dim, which requires dark skies to view them. Near the Harvest Moon and even in August near the full moon it takes nearly a week for that @#$%^&* Moon to get the heck out of the evening sky, so I don’t have to stay up till after midnight to see anything. That’s I why have this interest in the Harvest Moon. Know your enemy!
09/08/2022 – Ephemeris – We are going to have an early Harvest Moon this year
This is Bob Moler with Ephemeris for Thursday, September 8th. Today the Sun will be up for 12 hours and 53 minutes, setting at 8:06, and it will rise tomorrow at 7:14. The Moon, 2 days before full, will set at 5:54 tomorrow morning.
We are going to have an early Harvest Moon this year, on the early morning of Saturday the 10th, this Saturday coming up. The Harvest Moon is the closest full moon to the autumnal equinox, which is on the 22nd. The earliest a Harvest Moon can fall is on the 8th of September. The reason that the Harvest Moon is so famous is that at sunset the Moon’s path, in the sky, is shallow to the horizon. So it rises much less than its average 50 minutes later each night. This effectively lengthens the amount of useful twilight, allowing more time to harvest the crops. It compensated for the rapid retreat of the daylight hours this time of year. It’s not so important now, but back before electric lights it definitely was.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.
Addendum
The Harvest Moon rising as seen in Stellarium. The planetarium program Stellarium, which I use a lot, also colors the rising and setting Moon and Sun. It also reproduces the effect of atmospheric refraction, which makes objects close to the horizon look higher than they are. Thus, extended objects close to the horizon appear squashed a bit vertically.
The Harvest Moon effect is a phenomenon where the Moon’s nightly advance in rising times become much shorter than the average 50 minutes. This has the effect of extending the bright part of twilight for up to a week near the Harvest Moon. Complicating effects this year are the fact that the Harvest Moon is a supermoon, being a bit brighter than normal, and also moving faster than normal, negating the harvest moon effect somewhat. The Moon’s perigee was on the 7th, so the Moon is slowing down*, which shows in the delay numbers. Also helping to shorten the delay is that the path of the Moon is a bit shallower than the ecliptic. The Moon is south of the ecliptic, heading northward to its ascending node.
The Moon moves fastest in its orbit at perigee, and its slowest at apogee, at its farthest from the Earth.
08/24/2021 – Ephemeris – The Harvest Moon is coming next full moon
This is Bob Moler with Ephemeris for Tuesday, August 24th. Today the Sun will be up for 13 hours and 36 minutes, setting at 8:33, and it will rise tomorrow at 6:57. The Moon, 2 days past full, will rise at 10:00 this evening.
We are at that time of year when the advance in Moon rising times from night to night is shorter than the average 50 minutes per night. Tonight the Moon will rise only 21 minutes later than it did last night, and tomorrow’s Moon will rise 20 minutes later than it will tonight. It’s what I call the harvest moon effect, though Harvest Moon will be next month. I find the effect lasts for three full moons, centered on the start of autumn. That’s because the angle of the Moon’s and also the Sun’s paths in the sky called the ecliptic intersect the horizon at a shallow angle near sunset. It’s also the reason Venus will stay close to the western horizon for its evening appearance this year. The planets also hang around the ecliptic, where the zodiacal constellations are.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.
Addendum
The autumn vs spring sunset ecliptic (orange line). I’m using the autumnal equinox 2021 and vernal equinox 2022 as examples. At the autumnal equinox sunset, the ecliptic runs low in the south, and the ecliptic meets the horizon at a low angle. At the vernal equinox in March, the ecliptic runs very high in the south. It meets the horizon at a steep angle. Click on the image to enlarge it. Created using Stellarium and GIMP.
Near the autumnal equinox, the ecliptic appears low in the south at sunset. Planets near the Sun like Venus are seen low in the west and set soon after sunset. At the opposite end of the sky, a rising Moon near full will rise at less than the 50 minutes later each night average.
09/13/2019 – Ephemeris – Harvest Moon tonight
Ephemeris for Friday, September 13th. Today the Sun will be up for 12 hours and 38 minutes, setting at 7:57, and it will rise tomorrow at 7:20. The Moon, 1 day before full, will rise tonight 8:12.
Tomorrow is the Harvest Moon. In fact the instant of full moon is 12:33 a.m. tonight, so one could consider the Harvest Moon tonight. Funny thing though, this morning the Moon will reach apogee from the Earth, of 252 thousand miles (406 thousand km), making it the opposite of a super moon, a mini moon. I bet you wouldn’t notice if I didn’t tell you. The Harvest Moon is the name given to the nearest full moon to the autumnal equinox. It is a special time of the lunar cycle when the Moon rises much less than the 50 minutes later average each night. This appeared to extend twilight allowing farmers before the advent of electric lights extra time to gather in their crops each day.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Harvest Moon effect from September 11 to the 15th, 2019. Note the shallowness of the ecliptic and Moon’s motion near sunset in this period. Click on the image to enlarge. Created using Cartes du Ciel (Sky Charts).
09/25/2018 – Ephemeris – The harvest moon effect
Ephemeris for Tuesday, September 25th. The Sun will rise at 7:33. It’ll be up for 12 hours and 1 minute, setting at 7:34. The Moon, 1 day past full, will rise at 8:17 this evening.
The full, or nearly full moon, just rising, looks like a large orange pumpkin. The color, like the red of the sunset is caused by the scattering out of blue light by the atmosphere. It can happen at any full moon, not just the Harvest Moon, which was officially yesterday. What the Moon around the Harvest Moon does do is rise only a little later each evening. This helped the farmers in earlier times extend daylight to bring in the crops. On average the moon rises or sets 50 minutes later each night. However when the Moon is in the part of the sky where it is moving northward as well as eastward, then it rises only a little later each night. Tomorrow’s Moon will rise only 27 minutes later than it will this evening.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Bob Moler's Ephemeris Blog 