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SKY HAPPENINGS

Moab UT (at City Hall)
38O34’ N Latitude 109O33’ W Longitude
4048 ft - 1234 m

The Sky for December 2015
By Faylene Roth

 

Sunrise-Sunset
for December

(The time of sunrise and sunset assumes a flat horizon. Actual time may vary depending upon the landscape.)

DATE

SUNRISE

SUNSET

1

7:17am

4:57pm

2

7:18am

4:57pm

3

7:19am

4:57pm

4

7:20am

4:57pm

5

7:20am

4:57pm

6

7:21am

4:57pm

7

7:22am

4:57pm

8

7:23am

4:57pm

9

7:24am

4:57pm

10

7:25am

4:57pm

11

7:26am

4:57pm

12

7:26am

4:57pm

13

7:27am

4:58pm

14

7:28am

4:58pm

15

7:29am

4:58pm

16

7:29am

4:58pm

17

7:30am

4:59pm

18

7:30am

4:59pm

19

7:31am

5:00pm

20

7:32am

5:00pm

21

7:32am

5:00pm

22

7:33am

5:01pm

23

7:33am

5:01pm

24

7:34am

5:02pm

25

7:34am

5:03pm

26

7:34am

5:03pm

27

7:35am

5:04pm

28

7:35am

5:05pm

29

7:35am

5:05pm

30

7:35am

5:06pm

31

7:36am

5:07pm

Cygnus the Swan takes a nosedive on the western horizon pointing still towards the unseen center of our galaxy. In this position, it is often called the Northern Cross. From Cygnus follow the Milky Way west to east across the northern sky, redirecting your gaze towards the outer edge of our galaxy: through Cassiopeia, Auriga, Gemini, Orion, Canis Minor, and Canis Major. The bright stars studding the eastern sky are Capella (Auriga), Aldebaran (Taurus), Castor and Pollux (Gemini), Betelgeuse and Rigel (Orion), Procyon (C. Minor), and Sirius (brightest and nearest of all in C. Major).

Twilight extends the period of daylight in three stages at each end of the day. Morning twilight begins with astronomical twilight—about 1-1/2 hours (nearly 2 during summer months) before sunrise—as the eastern horizon brightens. Nautical twilight continues—as the overhead sky turns blue and color returns to the surrounding landscape—for another 30-40 minutes. The final stage—civil twilight—provides adequate light for most outdoor activities for the half hour before the sun crests the horizon. The opposite progression occurs after sunset.

DAYLENGTH
The interplay between later sunsets and later sunrises contributes to a fairly consistent period of daylight throughout December. The shortest days of the month—December 19-23—measured at 9 hours, 28 minutes, vary by only a few seconds.

WINTER SOLSTICE
When the sun’s position on the ecliptic hovers above the Tropic of Capricorn, 23.5 ̊ S latitude, on December 21 at 9:48pm, we in the United States will celebrate the progression of the seasons from autumn to winter. Many European countries, however, place the beginning of the winter season in early November and consider the solstice to be the mid-point of the season. Meteorologists in the U.S. designate the months of December, January, and February as the winter season since the coldest average temperatures in the northern hemisphere occur during these months.

MOON HAPPENINGS
December 3 – Dark evening skies. A waning last quarter moon rises after midnight.
December 11 – Dark sky period for several days before and after the new moon (3:29am).
December 18 – Bright evening skies. A waxing first quarter moon sets after midnight.
December 24/25 –Moonrise on 12/24 (4:51pm) is closer to the actual full moon (12/25 at 4:11am) than the 12/25 moonrise (5:58pm).
(The moon rises later each day—as little as 30 minutes to as much as one hour. Time of moonrise and moonset may also be delayed in mountainous terrain.)

VISIBLE PLANETS
Jupiter – Regulus, Jupiter, Mars, and Venus form an arc above the eastern horizon each December morning. Regulus sits at the heart of Leo. Jupiter hangs below the lion’s tail. Look for Jupiter after 1:00am at the beginning of the month but before midnight by month’s end. A waning last quarter moon passes by Regulus then Jupiter between the mornings of December 2-4. In the wee hours of December 30-31 a waning moon near first quarter again moves past Jupiter. (Magnitude -2.0)
Mars -- Mars rises a few hours after Jupiter in Virgo. Look for it between Jupiter (above) and Venus (below). Mars appears very small and faint, but it can be easily identified by its reddish hue. By the morning of December 5 the waning quarter moon has moved below Mars. (Magnitude +1.4)
Venus – The dominant planet of the morning sky is the last to rise. Look for it around 4:00am with Spica (Virgo) to its lower right. By December 7 the waning crescent moon rises with Venus slightly below. (Magnitude -4.0)

Apparent magnitude values range from -4 to +6 for most planets and visible stars. The lower the value the brighter the object. A decrease of 1.0 magnitude is 2.5 times brighter.

Primary Sources: USGS; U.S. Naval Observatory; Your Sky at http://www.fourmilab.ch/yoursky/
To find out when the space shuttle and International Space Station are visible from your location, go to: http://spaceflight.nasa.gov/realdata/sightings/index.html and click on Sighting Opportunities.

MAJOR CONSTELLATIONS this MONTH


Overhead
Ursa Major
Ursa Minor
Cepheus
Cassiopeia
Perseus
Andromeda
Aries
Pisces
Cetus

Eastward
Auriga
Gemini
Taurus
Orion
Canis Minor
Canis Major

Westward
Lyra
Cygnus
Pegasus
Aquarius


MAJOR METEOR EVENTS
Shower
Peak
(December)
Range
(December)
Constellation Radiant
Rate
(/hr)
Details
Conditions
Geminids

13/14
4-16
Gemini
5-120
10pm-dawn bright, colorful, medium-slow
New moon provides dark skies
Best time to view any meteor event is between midnight and morning twilight when the radiant is overhead. Trace the path of any meteor backwards through the sky to reach its radiant--the region of the sky from which meteors appear to originate.

The star chart approximates the sky from astronomical twilight to midnight. As the night and month progresses, the constellations shift toward the northwest. The celestial equator is measured in hours (h). The ecliptic is measured in degrees

Note: Hold your hand at arm’s length to measure apparent distances in the sky. The width of the little finger approximates 1.5̊. Middle, ring, and little finger touching represent about 5̊. The width of a fist is about 10̊. The fist with the thumb extended at a right angle equals 15̊. The hand stretched from thumb to little finger approximates 20̊-25̊. The diameter of both the full moon and the sun spans only 0.5̊. Adjust for the size of your hand.

 

 
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