THE SOUTHWORTH PLANETARIUM

70 Falmouth Street      Portland, Maine 04103

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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded January 1970

2021-2022: LIV

"Oh, don't let's ask for the moon. We've already got the stars."

-Bette Davis

THE DAILY ASTRONOMER

Tuesday, December 7, 2021

December 2021 Night Sky Calendar Part IV

Earliest sunset?!

Although winter begins on December 21st, the earliest sunset (4:04 pm.) at our latitude occurs on December 13th. This discrepancy between the solstice and earliest sunset arises because Earth is not a uniformly dense sphere moving along a circular orbit. Instead, it is an oblate spheroid traveling along an elliptical orbit. Consequently, the earliest sunset and latest sunrise times do not occur on the December solstice. For our latitude, the latest sunrise time (7:15 a.m.) happens on January 5th.

WEDNESDAY, DECEMBER 22: MOON NEAR PRAESEPE

See the waning gibbous moon (89%  illuminated) near Praesepe, or the Beehive Star Cluster, this evening.    Praesepe is the only prominent feature within the faint zodiacal constellation Cancer the crab.  

As Praesepe is fainter than the Pleiades, the lunar light interference will likely wash the cluster out for the evening. All the same, the moon will at least guide to you the Cancer constellation, which is difficult to observe in all but the best conditions.

SUNDAY, DECEMBER 26: LAST QUARTER MOON

MONDAY, DECEMBER 27: MARS 4.5 DEGREES NORTH OF ANTARES! (PLATINUM EVENT!!!!)

Wait? How could the close approach of a faint planet only visible in the eastern pre-dawn sky and the star Antares be considered the month's most spectacular event? Well, the Mars-Antares appulse certainly won't be the brightest event. However, it is quite noteworthy because Mars will appear close to its stellar nemesis. The name "Antares" means "rival to Mars," as both appear reddish. Mars appears red because of iron oxide in its soil.

Antares' crimson tint is indicative of its comparatively low effective temperature. As for the rivalry, this time Antares prevails as the star will be almost twice as bright as Mars. Of course, one will find it difficult to observe them both as they'll rise around 5:30 a.m. this morning.

WEDNESDAY, DECEMBER 29: MERCURY 4.2 DEGREES SOUTH OF VENUS (OBSIDIAN EVENT!!!!)

Ok, so, we ran out of the traditional medal metals. Tonight one will see the two "inferior planets" together in the western evening sky! Distinguishing between them won't prove difficult as Venus will be 110 times brighter than its planetary companion. Mercury sets at 5:20 p.m, Venus follows about ten minutes later.

PLANET WATCH

MERCURY

The first world is not visible during the first half of December. However, it quickly ascends into the western evening sky starting around the third week. VERDICT: Truly, don't bother trying to find Mercury until late this month. Best date to find Mercury is the 29th when it will appear close to Venus!

VENUS (PICK PLANET!)

Of course Venus is the month's pick planet. After all, it attained its maximum brightness for the year earlier this month. While Venus will exit stage west in the early evening, it certainly enlivens the evening sky. VERDICT: Oh, even if you've just arrived home from a nerve-damaging commute, just snap a glance skyward and allow the incandescent Aphrodite to beguile your senses. Venus is always worth a look.

MARS

Well, we can assure you that Mars will be the pick planet NEXT December, when it will reach opposition. Now, the red planet remains low in the pre-dawn eastern sky and, at magnitude 1.6, is about as bright as Castor. However, keep your eye on Mars throughout 2022 as it draws closer to Earth and grows brighter in the sky. VERDICT: No worries if you're not inclined to wander out into the harsh pre-dawn cold just to glimpse Mars. The red planet will become easier to see throughout next year!

JUPITER

Jupiter and Venus make a lovely pair this month. Although only a third as bright as Venus, Jupiter still outshines all the night sky stars. We will watch Jupiter drawing closer to the setting Sun throughout the winter before vanishing in March.

VERDICT: Seeing Venus, anyway? Just look off a bit to the east to see Jupiter!

SATURN

Saturn is that dim planet between Venus and Jupiter! Though moderately bright, it pales in comparison to its two brilliant planetary cohorts. VERDICT: If you're seeing Venus and Jupiter, look between them to find Saturn. The ringed planet disappears into the dusk by mid-winter, so observe it while you can!

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