2021, October 29:  Venus, Greatest Elongation


October 29, 2021:  Venus reaches its greatest elongation from the sun.  It is in the evening sky with Jupiter and Saturn.  The crescent moon and Mercury are in the eastern sky before sunrise.

Chart Caption – 2021, October 29: Venus is at its greatest elongation.


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:20 a.m. CDT; Sunset, 5:48 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Venus is at its greatest separation from the sun as seen from Earth.  This is known as the planet’s greatest elongation.  The angular separation, or elongation, is 47.0°.

The planet is east of the sun, appearing in the western sky after sunset.  The full name is greatest elongation east.  It’s a somewhat confusing term.  Perhaps it is better named the evening greatest elongation.

During March, Venus passed on the far side of the sun and slowly emerged in the evening sky.  For sky watchers at the mid-northern latitudes, the planet’s visibility has suffered from the low angle the plane of the solar system makes with the western horizon. For several weeks, the planet was low in the sky.  In contrast, observers at southern latitudes have observed the planet high in the sky. From there the angle of the solar system makes a large angle with the horizon.

Venus revolves around the sun faster than Earth.  In the short term, the planet gains altitude each evening and sets later until early December when it sets nearly 3 hours after sunset.  The planet brightens as it overtakes our world. The faster planet passes between Earth and sun during early January 2022.  It then quickly moves into the morning sky for a spectacular apparition that has conjunctions with Mars, Saturn, and Jupiter.

Morning Sky

Chart Caption – 2021, October 29: Before sunrise, the crescent moon is between Regulus and Pollux.

The crescent moon, 44% illuminated, is over two thirds of the way up in the sky, between Regulus and Pollux. This space on the celestial dome is Cancer.  The constellation has no bright stars.  Look for the scene about an hour before sunrise.

Chart Caption – 2021, October 29: Forty-five minutes before sunrise, Mercury is about 8° above the east-southeast horizon.

Fifteen minutes later, Mercury is about 8° above the east-southeast horizon.  It has passed its greatest elongation and is moving back toward bright twilight.  The planet is bright.  The star Arcturus is in the east-northeast, higher than Mercury and over 30° to the upper left of the planet.

Evening Sky

Chart Caption – 2021, October 29: Evening Star Venus is in the southwest after sunset, 2.7° to the lower left of Theta Ophiuchi (θ Oph).

Evening Star Venus is low in the southwest in front of the stars of southern Ophiuchus after sunset.  The planet is 2.7° to the lower left of Theta Ophiuchi (θ Oph on the chart).  The planet is stepping through the constellation, moving into Sagittarius in a few evenings.  Venus is 8.5° from Alnasl, “the point of the arrow” of Sagittarius.

Chart Caption – 2021, October 29: Jupiter and Saturn are in the southern sky after sunset.

Farther eastward, bright Jupiter is in the south-southeast.  It is to the upper right of the star Deneb Algedi. A binocular may help locate the background star. 

Saturn is over 15° to the right of Jupiter and at about the same altitude above the horizon.  While Jupiter is in eastern Capricornus, Saturn is in front of the stars in the western part of the constellation. Both planets are slowly moving eastward compared to the starry backdrop.

Detailed Daily Note: One hour before sunrise, the moon (23.0d, 44%), in Cancer, is over 64° above the southeast horizon.  It is between Pollux and Regulus (α Leo, m = 1.3).  Fifteen minutes later, Mercury is nearly 8° up in the east-southeast. Venus is at its evening greatest elongation (47.0°) at 3:52 p.m. CDT.  Forty-five minutes after sunset, brilliant Venus is nearly 12° up in the southwest, 2.7° to the lower left of θ Oph. Venus sets 136 minutes after sunset. Farther eastward, Saturn is nearly 29° above the southern horizon.  Bright Jupiter – nearly at the same altitude as the Ringed Wonder – is 15.3° to the left of Saturn. Two hours after sunset, Saturn is about 28° up in the south-southwest, 1.3° below υ Cap.  Saturn, over 33° up in the south and east of the meridian, is 3.6° to the lower right of μ Cap, 1.9° to the upper right of Deneb Algedi.



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