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2021, September 25: Morning Moon, Evening Planet Pack

The Pleiades star cluster.

The Pleiades star cluster. (U.S. Naval Observatory)

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September 25, 2021:  The bright morning moon approaches the Pleiades star cluster and Aldebaran.  In the evening sky, brilliant Evening Star Venus, Jupiter, and Saturn are easy to spot.

Chart Caption – 2021, September 25: One hour before sunrise, the moon is to the lower right of Pleiades star cluster and Aldebaran.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:42 a.m. CDT; Sunset, 6:42 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Note from the sunrise and sunset times, the length of day and night are equal today.  While the equinox occurred a few days ago, the lengths are equal today from the definitions we use for sunrise and sunset as well as refraction of the sun’s disk when it is near the horizon.

Morning Sky

An hour before sunrise, the bright moon, 82% illuminated, is high in the southwestern sky.  It is closing in on the Pleiades star cluster and the bright star Aldebaran.  The lunar orb’s glare makes it difficult to see the dimmer starfield.  Stand in the shadow of a house or building to see the dimmer stars or use a binocular to see them. 

The moon is over 9° to the lower right of the Pleiades star cluster, and nearly 18° to the lower right of the star Aldebaran.

Tomorrow morning look for the moon between the star cluster and the star.

Evening Sky

Three bright planets, Venus, Jupiter, and Saturn, continue to gleam from the evening sky.  Brilliant Venus steps eastward from night to night in the southwestern sky.  The planet is moving in front of the sidereal background of the Classic Scorpion, Libra and Scorpius.

Chart Caption – 2021, September 25: In the southwest, Evening Star Venus moves eastward through the Classic Scorpion.

Forty-five minutes after sunset, find Venus low in the sky, over 8° above the horizon.  Neighborhood trees, houses, buildings, other obstructions can block the view.  The planet is 2.9° to the lower left of Zubenelgenubi – “the southern claw of the scorpion.”

Notice the red-orange star Antares – “the rival of Mars” – to the upper left of Venus.  Locate Dschubba – “the scorpion’s forehead” – to the right of Antares.

Venus passes Dschubba on October 9.  The moon is also very close, making a rare grouping of Venus, the moon, and the trio of stars that represent of the head of Scorpius.  On that evening, the five objects fit into a binocular field.  This is not observable again until October 10, 2029.

Chart Caption – 2021, September 25: Bright Jupiter and Saturn in the southeast after sunset, retrograding in Capricornus.

Farther eastward this evening, Jupiter is less than one-third of the way up in the southeast.  After Venus, it is the brightest “star” in the evening sky.  Dimmer Saturn is to the right of the Jovian Giant.

Saturn does not look so bright when compared to Jupiter, but after the giant planet prototype, Saturn is only dimmer than Arcturus and Vega this evening.

Both planets are slowly retrograding in Capricornus.  This westward motion of the outer planets compared to the stars is an illusion as our planet passes between the planets and the sun and moves away.  Both continue this pattern until next month. 

Use a binocular to spot Jupiter near Deneb Algedi, “the kid’s tail,” and Nashira, “the lucky star of the verdant fields at the end of summer.”  Saturn is farther westward in Capricornus, 1.3° to the lower right of the dim star Upsilon Capricorni (υ Cap on the chart).

Capricornus is a relatively dim constellation.  The figure is part goat and part fish.  When connected with imaginary lines, the pattern resembles a futuristic airplane.

Find this planet pack in the evening sky until the end of year.Detailed Daily Note: One hour before sunrise, the moon (18.4d, 82%), nearly two-thirds of the way up in the southwest, is 9.2° to the lower right of Alcyone and 17.8° to the lower right of Aldebaran (α Tau, m = 0.8). Venus, Jupiter, and Saturn continue to sparkle in the evening sky.  Venus is rapidly moving eastward compared to the Classic Scorpion, but pokey giant planets Jupiter and Saturn are slowly retrograding in Capricornus.  Forty-five minutes after sunset, brilliant Venus is over 8° up in the southwest, 2.9° to the lower left of Zubenelgenubi and 22.9° to the lower right of Antares.  Through a telescope, Venus displays an evening gibbous phase that is 64% illuminated and 18.0” across.  Bright Jupiter, 95.9° of ecliptic longitude east of Venus, is over 21° above the southeastern horizon.  Saturn, at nearly the same altitude as Jupiter, is 16.0° of ecliptic longitude west of the Jovian Giant.  Two hours after sunset, Saturn is about one-third of the way up in the southern sky, east of the meridian.  It is 1.3° to the lower right of υ Cap.  Use a binocular to see the dimmer stars with the planets.  Jupiter, at about the same altitude as Saturn and in the south-southeastern sky, is 3.0° to the lower right of μ Cap, 1.5° to the upper right of Deneb Algedi, and 1.7° to the upper left of Nashira.  Four hours after sunset, the moon (19.1d, 76%) is nearly 15° up in the east-northeast.  The lunar orb is 5.2° below Alcyone.  The moon and the Pleiades star cluster snugly fit into the same binocular field.  Once you have seen this view, move the binocular so that the Pleiades are centered in the field to remove the moon and its gibbous glare from the field of view.

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