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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 2012
By Faylene Roth


DAYLENGTH
The period of daylight continues to shorten until December 18 when the length of the daylight period levels off at 9 hours 28 minutes for the next four or five days. By December 24 the days are lengthening but only average a gain of one-half minute per day through the end of December. Civil twilight adds about one half hour of usable light at dawn and dusk. During the next half hour—nautical twilight—color and detail disappear from the surrounding landscape and overhead skies become dark. At the end of the final stage of twilight—astronomical twilight—residual light of the setting sun fades below the horizon.

WINTER SOLSTICE
Winter begins in Moab on December 21 when the sun appears at its southernmost point in the sky at 4:12am as seen from the northern hemisphere. The sun appears overhead at 23.5 degrees south latitude which is marked on geographical maps as the Tropic of Capricorn because the sun was in the constellation Capricornus at solstice time when the maps were made. Today, due to precession of the equinoxes which is caused by the wobble of the earth’s axis, the sun is at the same latitude but appears farther west in the constellation Sagittarius when the winter solstice occurs.

Sunrise-Sunset
For December 2012

Day Sunrise Sunset
1
7:17am
4:57pm
2
7:18am
4:57pm
3
7:19am
4:57pm
4
7:20am
4:57pm
5
7:21am
4:57pm
6
7:22am
4:57pm
7
7:23am
4:57pm
8
7:24am
4:57pm
9
7:25am
4:57pm
10
7:25am
4:57pm
11
7:26am
4:57pm
12
7:27am
4:58pm
13
7:28am
4:58pm
14
7:28am
4:58pm
15
7:29am
4:58pm
16
7:30am
4:59pm
17
7:30am
4:59pm
18
7:31am
4:59pm
19
7:31am
5:00pm
20
7:32am
5:00pm
21
7:33am
5:01pm
22
7:33am
5:01pm
23
7:33am
5:02pm
24
7:34am
5:02pm
25
7:34am
5:03pm
26
7:35am
5:04pm
27
7:35am
5:04pm
28
7:35am
5:05pm
29
7:35am
5:06pm
30
7:36am
5:07pm
31
7:36am
5:07pm

MOON HAPPENINGS
Dec 6 – Last Quarter Moon rises soon after midnight.
Dec 13 – New Moon occurs at 1:42am.
Dec 19 – First Quarter Moon sets in the early am hours.
Dec 28 – Full Moon occurs at 3:28am. Watch it rise on the 27th (4:50pm)
and the 28th (5:45pm)pm.
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

METEOR HAPPENINGS
One of the year’s best meteor events—the Geminid Meteor Showers—is active from December 6 through December 18. Peak activity coincides with the new moon this year on the night of December 13/14. With clear skies, viewers can expect to see up to 60 meteors and fireballs per hour between 1:00am and 5:00am. Debris from an asteroid—rather than a comet—produces these multi-colored meteors.

The Delta Arietid and the Ursid Meteor Showers occur later in the month, but good viewing will be obscured by a waxing gibbous moon. Meteor activity for the Arietids (constellation Aries—just west of Jupiter) peaks on the night of December 20/21. The Ursids peak on the night of December 22/23. Consider viewing in the pre-twilight hours of the morning after the moon has set.

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

VISIBLE PLANETS
Jupiter – Mighty Jupiter shines in the eastern sky as evening twilight fades and remains visible into the early morning hours near the constelllation Taurus. It reaches opposition on December 3. At opposition the planet is on the opposite side of Earth from the sun which brings it to its closest position to the earth for this year. On December 25 Jupiter rises just ahead of a waxing gibbous moon. They appear less than two degrees apart. (Magnitude -2.8)

Mars – On December 14 look for the red planet in the evening twilight to the right of a very thin waxing crescent moon. Both Mars and the moon may be easier to find on December 15 when the planet appears below a slightly larger moon. Mars begins the month in Sagittarius and moves into Capricornus before month’s end which keeps it very low on the western horizon. (Magnitude +1.2)

Mercury – The innermost planet is never easy to see, but those who care enough to try may find it in the morning sky during the first two weeks of December. Look for it in Scorpius less than 10 degrees below Venus in the eastern sky. On December 4 Mercury reaches its greatest apparent distance from the sun which can improve its visibility. (Magnitude -0.3)

Saturn –
At the beginning of December Saturn rises with Virgo about one-half hour before Venus in the early morning twilight. The ringed planet rises earlier each day—between 3:00am and 4:00am by month’s end which means it will appear to move from Virgo into Libra. Look for a spectacular showing on the mornings of December 9 and 10 with a waning crescent moon hanging above Saturn and with Venus and Mercury below. Magnitude +0.6)

Venus – The “star” of the morning sky rises a little later each day which keeps it close to the southeastern horizon throughout the month. It’s in the constellation Scorpius. The spectacular morning event mentioned above continues on December 11 with a very thin waning crescent moon above Venus. Saturn glows above the moon and a fainter Mercury shines below Venus. (Magnitude -4.0)

Note: 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

Andromeda
Aries
Auriga
Perseus
Pegasus
Pisces
Triangulum

Northward

Cassiopeia
Cepheus
Ursa Major
Ursa Minor

Eastward

Canis Minor
Gemini
Orion
Taurus

Southward

Aquarius
Canis Major
Cetus

Westward

Cygnus
Lyra

The Milky Way spans the northern sky from west to east studded with brilliant stars in Cygnus, Cassiopeia, Auriga, Orion, Gemini, Canis Major and Minor. The long neck and broad wings of Cygnus the Swan takes on the appearance of a cross as it dives towards the western horizon. Andromeda the Galaxy appears high above—a faint fuzzy glow off the northeast corner of Pegasus in the constellation Andromeda.


Hold the star chart high above your head and match the compass directions to the direction you are facing. Adjust the star chart by orienting Ursa Major (Big Dipper) to match its position in the sky.

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.

Moab sky Map for December 2012
 
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