2021, September 7, 8: Mercury, Lunar Crescent

September 7 & 8, 2021:  The crescent moon, emerging from bright sunlight after its New moon phase, appears near Mercury on these evenings.  On September 8, use a binocular to find the crescent 5.0° to the upper right of the speedy planet.

2021, September 7& 8: The thin moon appears near Mercury on these evenings. This chart shows them at 25 minutes after sunset.
Chart Caption – 2021, September 7& 8: The thin moon appears near Mercury on these evenings. This chart shows them at 25 minutes after sunset.

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by Jeffrey L. Hunt

Mercury is nearing its evening greatest elongation, although the apparition is difficult to observe from the mid-northern latitudes.  The moon reached its New moon phase on September 6.

Mercury is visible about 15° to the lower right of brilliant Venus at 25 minutes after sunset.  It is hiding in the bright light of early evening twilight.  Use a binocular to locate Mercury about 4° up in the west.  The moon makes a wide pass on the evenings of September 7 and September 8.

Here’s what to look for:

September 7: Find a clear western horizon, free from houses, buildings, trees and other obstructions.  About 25 minutes after sunset, Venus is visible to the unaided eye, over 10° up in the west-southwest.  Mercury is nearly 15° to the lower right of Venus.  The speedy planet is nearly 5° above the horizon and about 13° south of the west cardinal point.  The crescent moon is only 1% illuminated.  It is about the same altitude – height above the horizon – as Mercury and a few degrees north of the west cardinal point.

2021, September 8: Through a binocular, the crescent moon is 5.0° to the upper right of Mercury.
Chart Caption – 2021, September 8: Through a binocular, the crescent moon is 5.0° to the upper right of Mercury.

September 8:  Under the same conditions as last night, the moon is to the upper left of last evening’s position. The moon’s phase is 5% illuminated. The Mercury – Moon combination is easier to locate, although this occurs during bright twilight.  The moon is 5.0° to the upper right of Mercury.  Both fit into the same binocular field of view.

Tomorrow evening the moon is near Venus.  Meanwhile, bright Jupiter and Saturn are in the southeastern sky during the early evening.

Detailed Daily Note for September 7, 2021:Twenty-five minutes after sunset, Mercury is over 4° up in the west-southwest. The razor-thin crescent moon (1.0d, 1%) is about 4° up in the west, slightly north of the west cardinal point.  The lunar slice is 14.6° to the right of Mercury.  In the precision used in these notes, the age of the moon is 1.0d, but in the Chicago region at this time, the moon is 14 minutes shy of that complete day.  For locations farther westward, the moon is a little higher in the sky at this time interval. Use a binocular to locate the moon and the speedy planet.  At forty-five minutes after sunset, Venus is about 8° up in the west-southwest, 2.9° to the upper left of Spica.  Yesterday at this time interval, Venus was very close (0.1°) to 76 Vir.  This evening Venus is 1.2° to the upper left of that star, showing the rapid eastward movement of the brilliant planet along the plane of the solar system. Venus, Spica, and 76 Vir fit into the same field of view of a binocular this evening.  At this hour, Saturn is over 20° up in the southeast, 17.0° to the upper right of Jupiter.  The Jovian Giant is over 15° above the horizon in the southeast.  Two hours after sunset, Saturn is nearly 27° above the south-southeast horizon, 1.0° to the lower right of υ Cap.  Saturn slowly creeps west as it retrogrades.  Jupiter, retrograding in Capricornus along with Saturn, is over 25° up in the southeast, 4.2° to the upper right of ι Aqr, 1.4° to the lower right of μ Cap, and 1.7° to the upper left of Deneb Algedi.

Detailed Daily Note for September 8, 2021: Twenty-five minutes after sunset, the crescent moon (2.0d, 5%) is over 8° above the western horizon.  It is 5.0° to the upper right of Mercury.  Both fit into a binocular’s field of view. Twenty minutes later, brilliant Venus – stepping eastward in Virgo – is about 8° up in the west-southwest, 4.0° to the upper left of Spica and 2.3° to the upper left of 76 Vir.  Two nights ago, Venus had a close conjunction with 76 Vir.  The planet is moving eastward at about 1.1° of ecliptic longitude from night to night.  Farther eastward, Saturn is over 20° above the southeast horizon.  The Ringed Wonder is 17.0° to the upper right of Jupiter that is nearly 16° above the horizon.  Two hours after sunset, Saturn is over 27° up in the south-southeast, 1.0° to the lower right of υ Cap.  Jupiter – nearly 26° up in the southeast – is 4.3° to the upper right of ι Aqr, 1.6° to the lower right of μ Cap, and 1.6° to the upper left of Deneb Algedi.

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