2021, October 9: Rare Grouping, Venus, Crescent Moon, Scorpius’ Head

October 9, 2021: A Venus-moon conjunction in Scorpius. Look for brilliant Venus, crescent moon, and the head of Scorpius in the southwest after sunset.  About every eight years, Venus and the moon appear near the head of the Scorpion after sunset.  Look for them about 45 minutes after sunset.

2021, October 9: Forty-five minutes after sunset, look for brilliant Venus, crescent moon, and the Scorpion’s head low in the southwest.
Chart Caption – 2021, October 9: Forty-five minutes after sunset, look for brilliant Venus, crescent moon, and the Scorpion’s head low in the southwest.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:57 a.m. CDT; Sunset, 6:18 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

DAILY NOTES FOR OCTOBER 2021

This evening there is a rare grouping of brilliant Venus, the crescent moon, and the three bright stars that mark the head of the Scorpion.

Look into the southwestern sky about 45 minutes after sunset.

This grouping fits within a binocular field and it will not be visible like this again for another eight years, October 10, 2029.

2021, October 9: Venus, crescent moon, Graffias, Dschubba, and Pi Scorpii fit into the same binocular field.
Chart Caption – 2021, October 9: Venus, crescent moon, Graffias, Dschubba, and Pi Scorpii fit into the same binocular field.

The three stars of the Scorpion’s head – Graffias (β Sco on the chart), Dschubba (δ Sco) and Pi Scorpii  (π Sco) – span about 6.5°.  That nearly fills a binocular field.  Getting Venus and the moon into the same field of view as the three stars is infrequent.  Including the moon is more of a long-shot.

The crescent moon passes Venus every month, either in the morning sky or the evening sky.

Venus revolves around the sun about every 225 days, but it catches and moves between Earth and Sun every 584 days, known as inferior conjunction.  Venus’ last inferior conjunction occurred on June 3, 2020.  The next occurs January 8, 2022.

During the interval from inferior conjunction to inferior conjunction, Venus springs into the morning sky, shining brightly. Then it disappears behind the sun and slowly moves into the evening sky, only to return to inferior conjunction and back into the morning sky.

Nearly every eight years, a few days, Venus passes between Earth and sun on the same date.  In the sky, Venus passes in front of the same stars in the same places as eight years prior.

The path that Venus makes through the stars this year is the same as it made eight years ago, within a few days.

2029, October 10: Venus, crescent moon, Graffias, Dschubba, and Pi Scorpii fit into the same binocular field.
Chart Caption – 2029, October 10: Venus, crescent moon, Graffias, Dschubba, and Pi Scorpii fit into the same binocular field.

On October 10, 2029 – one eight-year Venusian cycle into the future, the scene is similar to tonight.

From North America, On October 13, 2045, the three stars, Venus, and the crescent moon fit very tightly into a binocular field of view.

Step outside this evening, to see this rare grouping of Venus, crescent moon, and the Scorpion’s head

See the detailed notes below for near-groupings and challenging observations of this quintet.

Detailed Daily Note: Mercury is at inferior conjunction at 11:18 a.m. CDT. Forty-five minutes after sunset, brilliant Venus is over 9° above the southwest horizon, 0.7° to the lower left of Dschubba.  The crescent moon (3.5d, 17%) is 2.6° to the upper left of Venus.  This grouping of Venus, Moon, the head of Scorpius – Graffias, Dschubba, and π Sco – is unusual. They fit within the field of view of a 7×50 binocular (7°).  As seen from Chicago, such a close grouping occurs only two more times before 2050 in a sky dark enough to see the stars with a binocular.  Unlike a grouping with a single star, the three stars of Scorpius, span nearly 6.5°, restricting the tight target. On October 10, 2029, one-complete Venusian cycle away, the grouping occurs again and easily fits into a binocular field of view.  In 2037, the moon is too far away to fit into the binocular field from North America.  On October 12, the moon passes nearly 3° north of Graffias around 03:00 UT for locations farther west of Chicago.  All fit into the field except of π Sco. In 2043, all fit into the field of view, but the moon sets 38 minutes after sunset. While Venus and the moon are visible, the three stars are dimmer in the bright twilight and possibly not visible. Locations farther south such as Johannesburg, South Africa, Santiago, Chile, and Honolulu, Hawaii see the five objects in the same field of view when the moon is somewhat higher in the sky.  For Sydney, Australia, the moon is not in the field of view with the other objects.  From Key West, Florida, and San Diego, California, the moon is near the horizon as night falls. The next grouping in 2044 is a tight squeeze for all five objects, but the moon is low in the sky 30 minutes after sunset.  This suffers from the same twilight brightness challenge as the 2043 grouping.  At the October 13, 2045 grouping – three, eight-year Venusian cycles in the future, the quintet makes a tight fit in the binocular field.  The group is more compact in regions east of Chicago.  Westward from this location, the moon is likely outside the field of view.  This evening, Venus is 9.5° to the lower right of Antares. Farther eastward, Saturn is nearly 27° up in the south-southeast, 15.5° to the right of bright Jupiter.  Two hours after sunset, Saturn is nearly 29° up in the south, west of the meridian.  In the starfield, the Ringed Wonder is 1.5° to the lower right of υ Cap.  Jupiter, nearly 32° above the south-southeast horizon, is 3.7° to the lower right of μ Cap, 2.0° to the upper right of Deneb Algedi, and 1.4° above Nashira.  Saturn’s retrograde ends in two evenings.

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