2023, December 4: Leo Moon, Mercury at Greatest Elongation

Venus, Mercury and the crescent moon,: March 18, 2018
Photo Caption – Venus, Mercury and the crescent moon,: March 18, 2018


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:02 a.m. CST; Sunset, 4:20 p.m. CST.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Chart Caption – 2023, December 4: This chart displays Mercury’s location with its orbital path at sundown.

Mercury reaches greatest elongation today.  The planet is visible at its maximum angular distance from the sun.  Mercury and Venus revolve around the sun closer than Earth and they are restricted to where they can appear, always centered on the sun.  In contrast, the outer planets can appear anywhere along the solar system’s plane, known as the ecliptic, and anytime during the night.

Mercury reaches the this point today at 8:28 a.m. CST.

The planet is east of the sun, meaning that it is visible in the western sky after sunset.  At this elongation, the planet’s visibility is further limited by the shallow angle the ecliptic makes with the horizon at this season.  This results in a poor showing for this appearance.  At sunset, the speedy planet is only 10° up in the southwest.  At thirty minutes after sunset, during bright twilight, the planet is over 6° above the horizon. A binocular is needed to see it in the bright twilight. Fifteen minutes later, it is about 4° up, still a binocular object as its light passes through the thicker layer of air near the horizon that dims and blurs celestial objects.  Overall, a challenging observation.

Chart Caption – 2024, March 24: Mercury’s location at sunset, with its imaginary orbit at sundown.

When Mercury reaches greatest elongation east again on March 24, 2024, the ecliptic’s angle at the horizon is large and the planet is over 17° up in the west at sunset.  At forty-five minutes after sundown, it is over 10° up in the sky, an excellent display for this planet!

Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24

Here is today’s planet forecast:

Morning Sky

Venus and Jupiter are nearing their planet-to-planet opposition in less than a week.  On that morning, Jupiter sets as Venus rises.  Afterward, Jupiter sets before Earth’s Twin planet appears above the horizon.  This morning, over three hours before sunrise, Venus is low in the east-southeast and Jupiter is low in the west. The pair is over 172° apart.  They are bright enough to shine through the horizon’s haze and are visible if the horizon is unobstructed.

Chart Caption – 2023, December 4: The moon is with Leo, high in the south before daybreak.

The moon is with Leo this morning.  An hour before sunrise, find the lunar orb, 57% illuminated, high in the south-southwest, 5.0° to the upper left of Regulus, the Lion’s brightest star.

Leo is a westward-facing character that we see in silhouette.  A backwards question mark, known as the Sickle of Leo, for its resemblance to a farmer’s cutting tool, marks the animal’s head.  The haunches and tail, identified as Denebola, is made by a triangle to the east of the sickle.

Regulus, meaning the prince, is the fifteenth brightest star visible from the mid-northern latitudes.  It is about eighty light years away, shining with a brightness of nearly 150 suns.

Chart Caption – 2023, December 4: Before sunrise, Venus and Spica are in the southeast.

Brilliant Venus is over 25° above the southeast horizon at this hour.  Stepping eastward in front of Virgo’s starfield, the Morning Star is 6.9° to the lower left of Spica.  It is heading toward a conjunction on the 17th with Zubenelgenubi, nearly 16° to the planet’s lower left and less than 15° above the horizon this morning.

Mars is rising before the sun, but not early enough to see it.

Evening Sky

Chart Caption – 2023, December 4: Mercury, at greatest elongation, is low in the southwest after sundown.

Arriving at greatest elongation, Mercury is 6° up in the southwest at thirty minutes after sundown.  Use a binocular.

Chart Caption – 2023, December 4: Saturn is in the south after sunset.

At an hour after sunset, Saturn is in the southern sky.  Moving eastward in front of Aquarius, the Ringed Wonder is 7.5° to the upper left of Deneb Algedi, Capricornus’ tail, 10.2° to the upper right of Skat, the Aquarian’s leg, and 10.7° to the lower right of Lambda Aquarii (λ Aqr on the chart).

Look for Fomalhaut, slightly dimmer than Saturn, nearly 20° to the lower left of the planet.

Chart Caption – 2023, December 4: An hour after nightfall, bright Jupiter is in the eastern sky.

Bright Jupiter is easy to spot, over 30° above the east-southeast horizon. It is still retrograding in front of Aries, 11.3° to the lower right of Hamal, the Ram’s brightest star, and 13.7° to the upper right of Menkar, the Sea Monster’s nostril.  A binocular might be needed to see the stars, especially in areas with outdoor lighting.

Chart Caption – Jupiter’s retrograde motion against the starfield is demonstrated for 2023.

Jupiter’s illusion of retrograde has carried it noticeably west of an imaginary line from Hamal to Menkar.  Retrograde continues until month’s end.

Use a binocular to inspect the Pleiades and Hyades star clusters.  The Pleiades, to Jupiter’s lower left, resembles a tiny dipper. Topaz Aldebaran, below the Pleiades and nearly 10° up in the eastern sky, is near the Hyades, and together they appear as a sideways letter “V,” making Taurus’ head.

In two evenings, Aldebaran rises at sunset and it is visible in the sky all night, setting in the western sky at sunrise.


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