2021, December 31:  Mars – Moon Conjunction, Four Evening Planets


December 31, 2021: This morning before sunup, the thin waning crescent moon appears near Mars and the star Antares.  Four planets – Venus, Mercury, Saturn, and Jupiter – are on parade in the southwest after sundown.

Chart Caption – 2021, December 31: The waning crescent moon is near Mars and Antares before sunrise.


by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:18 a.m. CST; Sunset, 4:30 p.m. CST.  Check local sources for sunrise and sunset times for your location.

Morning Sky

This morning the thin crescent moon – 7% illuminated – is low in the southeast before sunrise.  Find a clear horizon.  Mars is 3.9° to the lower left of the lunar slice.

If you’ve not seen Mars in the morning sky, the thin crescent points the way to it.

Mars is not as bright as might be expected.  It is brighter than nearly all the stars in the immediate region – except Antares – but it is not gleamingly bright. The Red Planet is over 200 million miles away this morning.

The planet reflects about 25% of the sunlight that strikes it and is only about half the size of Earth.

When it is close to us near its opposition, when Earth is between the planet and the sun, the planet’s presence in the night sky is unmistakable.  Now, nearly three months after its solar conjunction, the planet slowly climbs into the morning sky, fairly far from Earth on its Martian orbital path around the sun.

The star Antares, known as “the rival of Mars,” is 3.3° to the lower right of the lunar crescent and 5.2° to the lower right of Mars.

Antares marks the heart of the celestial Scorpion.  At this hour, most of its tail and body are below the horizon.  Its classic pincers Zubeneschamali and Zubenelgenubi, are higher in the sky and reach westward.

The moon reaches its New moon phase on January 2 at 12:33 p.m. CST.  It then appears as a thin sliver in the evening sky.  Look for Venus and the moon on the evening of December 6 for a spectacular conjunction.  The planet is near its brightest light along with a thin crescent moon.  This is the most photogenic appearance of the pair during this evening appearance of the planet and the moon.

Evening Sky

Chart Caption – 2021, December 31: Four evening planets – Venus, Mercury, Saturn, and Jupiter – are in the southwest after sundown.

After sundown, four bright planets are on parade in the southwest.  The brightest is Venus.  Look for it shortly after sunset because it is on a quick slide into bright sunlight and its inferior conjunction in about a week.

At forty-five minutes after sunset, the planet is only 4° up in the sky.  Bright Mercury is 6.7° to the left of the Evening Star.

At this hour bright Jupiter is about one-third of the way up in the southwestern sky, nearly 40° to the upper left of Venus.

Because Venus is very low in the sky and its sets only 70 minutes after sunset.  With its rapid departure from the evening sky, it is easy to mistake Jupiter for it.

Through a telescope, Venus is a razor-thin evening crescent phase that is only 2% illuminated.

Saturn is about midway between Jupiter and Venus.

Jupiter, Saturn, and Mercury are moving eastward along the plane of the solar system, while Venus is retrograding.

What is the last date that you see Venus in the evening sky?  Look earlier each evening.



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