What's Up in the Night Sky

December 2023 - Vol. 27, No. 12

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

Some believe the winter night sky is the most beautiful of the year! By mid-month, misty Pleiades, the famous open star cluster of the constellation Taurus, is visible due S. at 10 pm. Although part of the constellation Taurus, it lies above its "lazy V" asterism whose brightest star, orange-tinted Aldebaran, glows near the point of the lower branch of the "V". Above are the constellations Perseus, Cassiopeia (whose "W" shaped asterism is unmistakable) and Auriga. Lovely Orion, whose asterism reminds me of a slightly lopsided hour glass, moves upwards from the SE. Note its three "belt" stars located at the "pinch" of the hour glass. The hazy object below the middle belt star is M42, the Great Orion Nebula, a region of space where stars are being born. Orion is followed by the bright stars Procyon (Canis Minor) and Sirius (Canis Major). Along with the bright star Betelgeuse (Orion), these three stars form the famous "Winter Triangle". To the E shine the Gemini twins, Castor and Pollux. In the SW, the diamond-shaped "Great Square of Pegasus" stands on one corner while high in the N, Ursa Major's asterism, the Big Dipper, stands on its "bowl".

MERCURY reaches greatest elongation on the 4th, then moves toward the Sun, reaching inferior conjunction on December 22. VENUS remains in the morning sky this month. MARS is too close to the Sun to be seen. Brilliant JUPITER shines brightly as the night begins, fading to -2.7 mag after last month's opposition. SATURN in Aquarius, sets around 9pm. URANUS in the evening sky is still well placed for those with a dark site that may find the gas giant with unaided vision. Most will need optical aid to observe. NEPTUNE sets before midnight, resuming prograde motion on the 7th, it will return to Pisces mid-month.

Review how to determine Angular Measurement.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time. Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times or check with the U.S. Naval observatory. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
01	Pollux, Alpha Geminorum 1.6 deg. N of the Moon.
04	Mercury at greatest elongation E. Moon at apogee.
07	Neptune stationary.
09	Venus 4 deg. N. of Moon.
12	Alpha Orionis (Betelgeuse) occulted by asteroid 319 Leona visible to observers and Europe and southern United States. The maximum duration is 11.6 seconds, begins shortly after 1 UT for all locations. This is an excellent opportunity for astrophotographers! Go to Steve's Asteroid Occultation Page to get the details.
13	Mercury stationary.
14	Mercury 4 deg. N. of Moon. Geminid meteor peak. This meteor shower is unusual in that it is associated with the 3200 Phaethonan asteroid that orbits the Sun every 1.4 years. Most showers are associated with periodic comets. The Geminid shower is one of the most prolific meteor shower that may produce about 120 meteors per hour at its peak. Best observed after midnight.
16	Moon at perigee.
17	Saturn 2.0 deg. N. of Moon.
19	Venus at greatest heliocentric lat. N. Neptune 1.3 deg. N. of Moon, occultation from parts of E. Antarctica, S. edge of Australia.
22	Solstice, the shortest day of the year 2023. Jupiter 3 deg. S. of Moon.
23	Ursid meteor shower produces 10 meteors at its peak. (4 UT) Mercury at greatest heliocentric lat. S. Uranus 3 deg. S. of Moon.
24	Moon 1.0 deg. S. of the Pleiades (M-45).
27	November's full moon is often called the "Cold Moon" because it is marks the begin of the cold winter in North America.
28	Pollux, Alpha Geminorum 1.7 deg. N of the Moon.
30	Mercury at greatest helicentric lat. N.
31	Jupiter stationary.

Lunar Almanac for December 2023

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 12	Deep Space Objects
	1st. Qtr 19	Planets & Moon
	Full 26	Moon
	Last Qtr 04	Deep Space & Planets

Topic of the month: The Charioteer, Auriga

Awash in the winter Milky Way, rising behind Perseus is the constellation of the charioteer, Auriga. The constellation of Auriga is completely over the horizon in the mid-fall when evening comes to the northern latitudes. For some unclear reason, the charioteer is depicted with goats under his arm perhaps from the time that the constellation was associated with the Good Shepard. Auriga features Capella, whose name means little she goat, the northernmost first magnitude star as seen from planet Earth. At 45 light years distant, this star was discovered to be a double by spectroscope just before the turn of the 20th century. Later observations revealed that Capella was actually a multiple star system with at least 4 components.

The constellation Auriga is usually identified as a pentagon, but the star in the southern tip is El Nath, the Beta star of the constellation Taurus and not "officially" recognized as part of Auriga. Near Capella, three stars form an elongated triangle. Eta and Zeta are known as "the kids," part of the triangle formed with Epsilon Aurigae. Eta Auriga (Almaaz, or "he-goat") is one of the most interesting stars in the night sky. It is an eclipsing binary star, containing two stars that revolve around a common center, every 9,883 days or 27 years. For two years, the eclipsing binary system dims from 3.0 to 3.8 magnitude as an unseen companion star hides the view of the primary for Earthbound viewers. The last time this happened was in 2009-2011 and the star was studied intensely by variable star observers. Still, a conclusive model has not been constructed that explains the complete system dynamics.The best theories will be tested again in 2036.

Other stars in the constellation have well-known proper names as well. Beta Auriga is known as Menkalinan, itself an eclipsing binary, shines around mag 1.92 to 2.01 about 10 deg. East of Capella. Perhaps best remembered in Auriga, are the fine star clusters M36, M37, and M38. M36 is the smallest, consisting of 60 stars. M37 is the largest containing about 150 stars and is about 20' in diameter. M38 contains perhaps 100 stars and also has a smaller and fainter cluster of stars nearby, NGC 1907.

A number of galactic clusters lie in this region of the Milky Way, including NGC 1664 containing 40, 10th magnitude stars. NGC 2281 consists of 30 stars arranged in a crescent shape. Auriga offers a wealth of star clusters as well as variables and doubles to intrigue amateurs. This constellation never disappears in the Sun from the northern hemisphere and can be seen at some time every night of the year.

--See You Under the Stars!
Astra for Astra's Almanac