2023: Harvest Moon Effect

Harvest (Photo by Johannes)


by Jeffrey L. Hunt

Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24

The moon is Full at 4:57 a.m. CDT on September 29th and is so named the Harvest Moon. Traditionally, this moon aided agricultural societies at the mid-northern latitudes during their harvest times.

Photo Caption: A bright moon. (Photo by Roberto Nickson )

Every Full moon phase provides brightly illuminated landscapes, but the geometry of the solar system’s plane provides more-consistent moonlight during this season.

Throughout the month on average, the moon rises fifty minutes later each day-night cycle as the lunar orb moves eastward through its orbit.  During autumn evenings, the plane of the solar system, known as the ecliptic, makes a shallow angle with the eastern horizon near sunset.

Chart Caption – 2023, September: The locations of the moon are displayed at 45 minutes after sunset beginning September 24th through the 29th.

As the moon moves farther eastward, it moves 13° each evening compared to the starry background, but compared to the horizon, the moon’s altitude – height above the horizon – changes little. The accompanying chart shows the eastward place of the moon compared to Saturn and the eastern horizon from September 24th through the 29th at 45 minutes after sundown. The moon is farther eastward, but about the same altitude as the previous night.

A Full moon. Photo by João Luccas Oliveira on Pexels.com

Looking at moonrise times for Chicago, Illinois from the US Naval Observatory’s MICA computer program, the delay of moonrise is considerably less than the average. On the Full moon night, the delay from the previous night is only twenty-three minutes.

The following table shows moonrise and sunset times and the delay of moonrise on subsequent days.

DateMoonrise (CDT)Delay from Previous Day (minutes)Sunset (CDT)
Sept. 244:28 p.m.6:45 p.m.
Sept. 255:07 p.m.396:43 p.m.
Sept. 265:40 p.m.336:41 p.m.
Sept. 276:07 p.m.276:40 p.m.
Sept. 286:32 p.m.256:38 p.m.
Sept. 296:55 p.m.236:36 p.m.
Sept. 307:20 p.m.256:34 p.m.
Delay of Moonrise, September 2023

On those nights leading up to the Harvest Moon date, the bright moon easily provides light after sundown to work outside without the need for outdoor lighting.  On the Full moon night, the moon rises only nineteen minutes after sunset and while the landscape is brightly lit during the early phase of twilight.  Civil Twilight, about the time most street lights switch on, occurs 27 minutes after nightfall. The moon provides some light to perform some outside work during the early evening.

Chart Caption – 2024, March: Locations of the moon are displayed at 45 minutes after sunset, beginning March 21st through the 24th.

Looking ahead six months, a different geometric arrangement is in play with the March 2024 Full moon, known as the Worm moon, and the eastern horizon.  The ecliptic makes a higher angle with the eastern horizon, similar to the eastern morning sky during September 2023, giving a favorable view of Mercury. Unlike the autumn lunar path, the spring path is obviously different. The moon’s nightly altitude is sharply different as the Full phase approaches.

Photo Caption – Scenic view of beach during dawn (Photo by Alex Montes on Pexels.com)

During the rising sequence around the March 25, 2024, Full phase, the rising time interval from night to night is around 60 minutes. The moon does not linger near the horizon as it does during autumn.  While there are no traditional outdoor activities associated with this Full phase, the timings are greatly different from the September Full moon sequence.

The following table shows moonrise and sunset times as well as the delay of moonrise from the previous date.

DateMoonrise (CDT)Delay from Previous Day (minutes)Sunset (CDT)
March 213:41 p.m.7:05 p.m.
March 224:43 p.m.627:06 p.m.
March 235:45 p.m.627:07 p.m.
March 246:45 p.m.607:08 p.m.
March 257:46 p.m.617:09 p.m.
Delay of Moonrise, March 2024

It should be noted here that the short delay of moonrise occurs at any moon phase, when the ecliptic makes a shallow angle with the eastern horizon.  A waning crescent moon, First Quarter phase, Last Quarter moon, and any gibbous phase can show the short delays between rises times from night to night.

Photo Caption – 2023, August 30: Perigee Blue Moon (Photo by Tim S.)

This year, the Harvest Moon occurs when the moon is near perigee, the point in the orbit closest to Earth.  So, we will see articles and photographs celebrate the Harvest Supermoon. 



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