2021, September 30:  Morning Moon, Gemini Twins

Astronomy, Sky Watching
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September 30, 2021: An hour before sunrise, the crescent moon is near the Gemini Twins.

2021, September 30: An hour before sunrise, the crescent moon is 3.0° to the lower right of Pollux.
Chart Caption – 2021, September 30: An hour before sunrise, the crescent moon is 3.0° to the lower right of Pollux.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:47 a.m. CDT; Sunset, 6:34 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

An hour before sunrise, the thick crescent moon, 37% illuminated, is high in the southeastern sky.  It is 3.0° to the lower right of Pollux.  The star and Castor, 4.5° above Pollux mark the heads of the Gemini Twins.

In mythology, the Twins were sons with different fathers.  One is immortal and the other was mortal.  When Castor is killed in battle, Pollux pleads with Zeus to bring him back to life.  Zeus made them both immortal, on the premise that they would be in the sky half the time.

Castor is a blue-white star and over 50 light years away.  It shines with a brightness of nearly 70 suns. The star consists of three stars.  Each has another star revolving around it. Castor is 45th on the list of the brightest stars seen from Earth.

Pollux is closer, over 30 light years and shines as a topaz star.  While closer to our sun, Pollux shines with a brightness of 60 suns, making it appear brighter than its twin star.  It is the 15th brightest star in Earth’s night sky.

A planet named Thestias, revolves around Pollux at about a distance that is slightly larger than Mars’ distance from the sun.  It is measured to be at least twice the mass of Jupiter.

This morning, take a binocular outside and attempt to fit the crescent moon, Pollux, and Castor in the same field of view.  It’ll be a tight view.

Detailed Daily Note: The thick crescent moon (23.4d, 37%) is nearly two-thirds of the way up in the southeast at one hour before sunrise.  The lunar orb is 3.0° to the lower right of Pollux (β Gem, m = 1.2). At month’s end, daylight is reduced to 11 hours, 47 minutes. Venus, Jupiter, and Saturn are in the evening sky after sunset.  During the month, Venus moved 33.1° to the east.  In comparison, Jupiter retrograded 2.8°, while Saturn moved 1.1° westward compared to the stars.  At month’s end, Saturn is 74.2° of ecliptic longitude east of Venus.  Jupiter is 15.8° eastward along the ecliptic from Saturn, 90.0° east of Venus.  Forty-five minutes after sunset, Venus is nearly 9° up in the southwest, 1.6° to the upper left of ι Lib, 10.0° to the lower right of Dschubba, and 17.3° to the lower right of Antares.  Through a telescope, Venus is an evening gibbous, 62% illuminated and 18.8” across.  The planet is 45° east of the sun this evening. At this hour Jupiter and Saturn are in the southeastern sky.  After Venus sets, Jupiter is the brightest “star” in the sky.  Two hours after sunset, Jupiter is over 30° above the south-southeast horizon.  In the starfield, it is 3.3° to the lower right of μ Cap, 1.7° to the upper right of Deneb Algedi, and 1.5° to the upper left of Nashira.  Saturn is less than 30° above the southern horizon, east of the meridian, and 1.4° to the lower right of υ Cap.  Notice Fomalhaut (α PsA, m = 1.2), over 10° above the southeast horizon, is nearly 23° to the lower left of Jupiter.

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