2021, September 20: Harvest Moon, Bright Planets

September 20, 2021:  The Harvest Moon occurs at 6:55 p.m. CDT, the full moon that occurs closest to the autumnal equinox.  In addition to the full moon, three bright planets are in the evening sky – Venus, Jupiter, and Saturn.

a full moon in the night sky
Photo Caption – The rising full moon (Photo by João Luccas Oliveira)

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:36 a.m. CDT; Sunset, 6:51 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

This evening the full moon occurs at 6:55 p.m. CDT.  At the mid-northern latitudes, this seasonal full moon is known as the Harvest Moon in its link to the agricultural growing patterns.  This is the full moon closest to the autumnal equinox.

From North America, the moon rises about 30 minutes after sunset.

At this season each night, the moon rises less than 30 minutes later each evening, aiding farmers to collect their crops without the aid of electric lights.  (See more about the geometry of the Harvest Moon Effect in this article.)

During the next several years, the date of the Harvest Moon varies from September 10 (2022) until October 6 (2025).  On September 22, 2029, the full moon time occurs just 70 minutes before the equinox.

In addition to the Harvest moon, Venus, Jupiter, and Saturn are in the evening sky.  Venus is in the west-southwest after sunset.  It shines through the colors of evening twilight. The brilliant planet sets 95 minutes after sunset.

2021, September 5: Jupiter and Saturn in the southeast after sunset.
2021, September 5: Jupiter and Saturn in the southeast after sunset.

Bright Jupiter and Saturn are in the southeast after sunset.  They are easy to locate.  Their places do not change much from night to night.  They are low in the southern sky before midnight and they set in the southwest before morning twilight begins.

Detailed Daily Note: One hour before sunrise, the bright moon (13.4d, 99%) is just above the west-southwest horizon. The moon is at its Full (Harvest) moon phase at 6:55 p.m. CDT. Three bright planets are in the evening sky.  Forty- five minutes after sunset, brilliant Venus is over 8° above the west-southwest horizon and 4.2° to the lower right of Zubenelgenubi. Through a telescope, Venus is an evening gibbous phase, 66% illuminated and 17.3” across.  Farther eastward, the bright moon (14.0d, 100%) is less than 5° above the east horizon. Jupiter, about 20° above the southeast horizon, is over 35° to the upper right of the lunar orb.  Jupiter is 101.9° east of Venus.  While Jupiter is retrograding, Venus’ rapid eastward motion has cut the gap 24.0° since September 1. At this hour retrograding Saturn, 16.3° of ecliptic longitude to the upper right (west) of Jupiter, is over 23° above the south-southeast horizon.  As the calendar day ends, the moon is over 40° up in the south-southeast.  Jupiter is over one-third of the way up in the south-southwest.  Use a binocular to see the background stars.  Jupiter is 2.6° to the lower right of μ Cap, 1.4° to the upper right of Deneb Algedi, and 1.9° above Nashira.  Saturn is over 20° above the southwest horizon, 1.2° below υ Cap.

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