December 21, 2024: The winter solstice occurs this morning. The bright gibbous moon is visible before sunrise. Five bright planets shine during the nighttime hours.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 7:15 a.m. CDT; Sunset, 4:23 p.m. CST. Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.
Winter Solstice
The Winter Solstice occurs this morning at 3:21 a.m. Central Time. The sun shines most directly toward the southern hemisphere. It is overhead today at noon at the Tropic of Capricorn, latitude 23.5° South.
The sun reaches its most southerly point, signaling the beginning of astronomical winter in the northern hemisphere and the least daylight of the year, 9 hours, 8 minutes at Chicago’s latitude. For our southern hemisphere readers, summer begins. Have a great day at the beach!
Morning Moon
Before sunrise, the bright gibbous moon, 64% illuminated, over halfway up from the horizon to overhead, is in the southwestern sky. It is 14.4° to Regulus’ upper left, Leo’s brightest star, and 13.4° to Denebola’s lower right, the Lion’s tail.
The moon is at its Last Quarter phase tomorrow at 4:18 p.m. Central Time.
Regulus is the brightest star that is closest to the plane of the solar system, known as the ecliptic. Planets and the moon pass by closely. In comparison, Denebola is over 12° above the plane, with the moon and planets passing far below it.
Morning Mars
Farther westward, Mars shines brightly to the upper left of the Gemini Twins, Castor and Pollux. At an hour before daybreak, the Red Planet is less than halfway up in the west and 11.6° to Pollux’s upper left.
Mars retrogrades in front of Cancer. Earth passes between the planet and the sun on January 15th.
Mercury in Southeast
Fifteen minutes later, Mercury is making its final appearance of the year in the southeast. Rising 117 minutes before the sun, the speedy planet stands 10° above the southeast horizon.
Mercury is with Scorpius, 5.3° to Graffia’s lower left and 7.3° to Dschubba’s lower left, the Scorpion’s forehead. It is brightening, visible through the growing hues of morning twilight. Use a binocular to find the planet and the stars.
Antares, Scorpius’ brightest star, is nearing its helical rising – first morning appearance. This morning, it is less than 3° above the horizon. Its color blends with the reds of dawn’s early light, making it a challenge to see even through a binocular.
Scorpius is climbing across the southeast horizon. The body and tail are still below the horizon, while the head is immediately above the line where the sky meets the ground. Its claws, Zubenelgenubi and Zubeneschamali, are higher as the arachnid reaches westward. The Scorpion does not fully appear until the end of February when Antares is nearly south and the arc of its tail nearly drags along the southern horizon from Chicago.
Four Bright Planets after sunset
After sunset, four bright planets are visible along an arc of the ecliptic at about three hours after sunset. First appearing about 30 minutes after sundown, brilliant Venus is low in the west-southwest when looking for the planetary quartet. The Evening Star is closing in on Saturn, 27.0° to the brilliant planet’s upper left.
Jupiter in Eastern Sky
Farther eastward, bright Jupiter is halfway up in the eastern sky. It retrogrades between Taurus’ horns, 6.4° to Aldebaran’s upper left, the constellation’s brightest star, and 10.4° to Elnath’s lower right, the northern horn.
At this hour, Jupiter is the second brightest starlike object in the sky, but it shines at only 25% of Venus’ intensity, while Aldebaran is less than 20% as bright as Jupiter.
Evening Mars
Mars, the third brightest star until Sirius rises, is over 5° above the eastern horizon, 11.4° to Pollux’s lower left.
The five planets are visible for about another week, before Mercury disappears into bright morning twilight. Mars appears higher in the eastern sky each evening as Venus shines from the western sky, making the four planets easy to see simultaneously for the next several weeks.
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