What's Up in the Night Sky?

December 2021 - Vol. 25, No. 12

Astra's Star Gate

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 too close to the Sun to be seen most of the month after superior conjunction late last month. VENUS still favors the southern hemisphere in the evening sky, moves even closer to the Sun as it approaches inferior conjunction early next year. MARS appearing after conjunction, will be faintly visible in the early morning sky by the end of the month. JUPITER low in the evening sky, sets early. SATURN also disappears in the early evening. URANUS is visible most of the night. NEPTUNE in Aquarius, sets before midnight.

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.

01 Neptune stationary.
02 Mercury at aphelion.
03 Mars .7 deg. S. of Moon, occultation from Mongolia, NE China, parts of E. Russia, Japan, Micronesia, Polynesia, and Hawaii.
Venus at greatest extent illuminated.
04 A total solar eclipse over Antarctica in a narrow band will not be seen by many because it is so remote.
Moon at perigee, expect large tides.
07 Venus 1.9 deg. N. of Moon.
08 Saturn 4 deg. N. of Moon.
09 Jupiter 4 deg. N. of Moon.
14 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. The peak is unfortunately close to the full moon on the 18th of the month.
15 Uranus 1.5 deg. N of Moon.
18 Moon at apogee.
Venus stationary
19 Mars at descending node.
Moon 1.8 deg. N of M35.
20 Venus at ascending node.
21 Solstice, Sun located at its southernmost point in Earth's sky.
22 Ursid meteor shower produces 10 meteors at its peak.
23 Mercury at greatest heliocentric latitude S.
31 Mars 0.9 deg. N. of the Moon, producing an occultation visible in parts of tip of S. America, S. Australia and other islands in the far south.

Lunar Almanac for December 2021

Phases of the Moon Phase and Date(s) Best viewed before local midnight
new moon New
Deep Space Objects
first quarter moon 1st. Qtr
Planets & Moon
full moon Full
last quarter moon Last Qtr
Deep Space & Planets

Topic of the month: Celestial Twins

Welcome to the last month in our 25th year! The evening sky welcomes the northern hemisphere to longer nights and views of the celestial vault, while in the south night is shrinking and Summer has arrived. The constellation of Gemini should be visible from a modestly dark site by 10 pm for citizens of Earth in the northern hemisphere. For many human civilizations, the constellation was associated with twins. The constellation of Pegasus against a celestial grid

Two of the constellations bright stars, Castor and Pollux, are less than 5 degrees apart in the night sky from Earth although they are not gravitationally bound to each other. Pollux, the brighter of the two, shines at 1.14 and is easily the brightest star in the constellation. Despite its brightness, it has been designated as Beta Geminorum (Beta Gem). The star is much more yellow than its "twin" as it has a K0 spectral classification and is considered an orange giant. A mere 52 light years away, Castor (visual magnitude 1.93) was discovered to be a double star in 1678. As astronomical knowledge became more sophisticated, the system was eventually identified as a system of three components, now designated Castor A, B, and C. Castor A and B were studied by William Hershel in 1803, he identified that the stars were actually gravitational bound and thus, Castor A/B is the first true physical binary that was recognized. Castor A and B are separated by about 6 arc-seconds and their revolution period about 467 years. Castor B is a pair of stars, reported as type A5 in Burnham's Celestial Handbook. They are of a similar size and each is about 1-1/2 the size of our Sun. Castor C is a pair of red dwarf stars, each about half the mass of our own Sun. This component has been designated YY Geminorum due to its variable nature. Castor A and B have a faint companion (separated 72 arc-seconds) that have the same parallax and proper motion. With six individual stars gravitationally bound together, Castor is considered to be a sextuple star system.

Amateur astronomers will want to look for an object in the constellation of Gemini known as NGC 2392 or the Eskimo Nebula. This object is an excellent planetary nebula. Although it is not quite as large as the more popular "Ring Nebula", M57 in Lyra, NGC 2392 is brighter at 8th magnitude. The central star of this planetary is also much brighter. At 8th magnitude it is easily seen in amateur telescopes, whereas the central star of the Ring is too faint for the small telescope. Don't look at CCD images and expect your view to approach the color and detail of those. The visual observation has its own charm and wonder. On a good night the edges of the Eskimo's parka will thrill the eye.

No discussion of Gemini is complete without mention of the huge star cluster known as M35. This cluster spans an area greater than the full moon and is visible at dark sites with the naked eye. The cluster was known before the time of Messier, but was found in his catalog and so the M designation has remained. The cluster contains at least 120 stars covering an area of 30 light years. Viewing this object with an amateur instrument gives one the impression of many double stars. Also visible as a fuzzy patch of light in the same field of M35, is the rich cluster NGC 2158. This cluster is more distant than M35 and would take a large amateur instrument at high power to resolve into stars.

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

The star chart above was generated by Stellarium, a free open source planetarium program. The above image was created by Dawn Jenkins, using Stellarium and a graphic editing program to format the image for this web page. Editing was done for educational purposes only. Stellarium offers much more to amateur astronomers and is being used in planetariums and to guide telescopes in the field. Simple charts like the one above can be used on the internet for non-profit, illustration purposes. Thank you to the makers of this fine program from Astra's Star Gate.

This installment of "What's Up?" is ©2021 by Dawn Jenkins for Astra's Stargate. View Ron Leeseburg's Farewell Issue for information on where to find information such as is presented in this almanac.