What's Up in the Night Sky

December 2015 - Vol. 19, 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 Aldeberan, 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 will be visible after the first week of the month and well placed for northern observers. VENUS will shine brightly in the morning sky, a lunar occultation will be visible in North and Central America. MARS is still also in the morning sky, moving into Virgo. JUPITER rises in late evening. SATURN reappears in the morning sky this month, before month end. URANUS sets after 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. Unfortunately some of these events may occur during daylight hours in your area.

DATE	EVENT
02	Regulus 3.0 deg N. of Moon.
04	Jupiter 1.8 deg N. of Moon.
05	Moon at apogee.
06	Mars 0.1 deg N. of Moon occulatation in central and eastern Africa, Southern India, Indonesia and Australia.
07	Venus 0.7 deg S of Moon occultation from North and Central America and the Carribbean.
13	Saturn 3 deg S. of Moon.
14	Geminid meteor shower, up to 120 per hour! Viewers in the northern hemisphere should look in the evening sky while sourthern observers may have better luck after midnight.
20	Uranus 1.2 deg N. of Moon, occultation from parts of Antarctica, southern S. America and Falklands.
21	Moon at perigee.
22	Winter Solstice at 4:48 UT. The longest night in the northern hemisphere, the longest day in the south.
23	Mars 3.3 deg N. of Spica. Ursid meteor shower peak. This shower can produce up to 10 meteors per hour at its peak. Aldebaran 0.6 deg S. of the Moon occultation from Russia, Northern Asia, Northwest Africa, Eastern Canada and Europe.
26	Regulus 2.7 deg N. of Moon
30	Jupiter 1.5 deg N. of Moon.

Lunar Almanac for December 2015

Phases of the Moon	Phase and Date(s)	Best viewed before local midnight
	New 11	Deep Space Objects
	1st. Qtr 18	Planets & Moon
	Full 25	Moon
	Last Qtr 03	Deep Space & Planets

Topic of the month: The Charioteer, Auriga

cygnus 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 when 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 spectrocope 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 from the constellation of 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. 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 9883 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 2.01about 10 deg E. 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 sometime every night of the year.

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

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