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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 2010
By Faylene Roth

December days are clipped abruptly short. Earliest sunsets of the year linger over the first twelve days of the month, varying by less than one minute. Later sunsets then slowly extend the length of the afternoon another 10 minutes by month’s end, while later sunrises are shortening the day by 19 minutes. The shortest period of daylight this month is 9 hours 28 minutes, which occurs December 19-23. Sunrise and sunset times are calculated for a flat horizon. Actual times vary depending upon the surrounding landscape. Dawn and dusk extend the period of daylight. Civil twilight continues about one-half hour before/after sunrise. Nautical twilight marks the next half hour of changing light before/after civil twilight. Astronomical twilight illuminates the sky with a faint glow in the half hour before/after nautical twilight.

DATE

SUNRISE

SUNSET

1

7:17am

4:57pm

2

7:18am

4:57pm

3

7:19am

4:57pm

4

7:20am

4:57pm

5

7:21am

4:57pm

6

7:22am

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

7:27am

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

7:31am

4:59pm

19

7:31am

5:00pm

20

7:32am

5:00pm

21

7:32am

5:01pm

22

7:33am

5:01pm

23

7:33am

5:02pm

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

7:36am

5:06pm

31

7:36am

5:07pm

MOON HAPPENINGS
December 5 – New Moon occurs at 10:36am
December 13 – First Quarter Moon sets after midnight
December 21 – Full Moon rises at 5:38pm
December 28 – Last Quarter Moon rises after midnight
(The time of moonrise and moonset assumes a flat horizon. Actual time may vary.)

WINTER SOLSTICE
By the time the full moon rises on December 21, the sun will have reversed its southern progression through the sky. At 4:38pm the sun hovers directly overhead at 23.44 degrees south latitude. Thousands of years ago the sun was in the region of the sky defined by the constellation Capricorn when the winter solstice occurred. That is why world maps mark this latitude as the Tropic of Capricorn. Today, because of precession of the equinoxes (aka wobble of the earth’s axis), the sun appears west of this point at the winter solstice in the region of Sagittarius. Sagittarius is visible in the night sky during the summer months (east of Scorpius) very low on the southern horizon from our latitude.

METEOR ACTIVITY
The Geminid Meteor Shower provides the major source of meteor activity this month. Look for these bright white tailless meteors between December 7 and 17. The shower peaks on the night of December 13/14 and can produce over 100 meteors per hour. Gemini, the radiant for this meteor shower rises in the early evening. Meteors become easier to see as the radiant climbs higher in the sky. A first quarter moon sets soon after midnight which lessens its impact on the eastern sky, although best viewing will be after midnight. The Ursid Meteor Shower, with a radiant in Ursa Minor (Little Dipper), peaks on the night of December 21/22. A full moon in the sky all night washes out most of these meteors, which are known for their flashy tails. The Ursids continue activity through December 26, so continue to scan the northern sky later in the week during the early evening hours before the moon rises.

LUNAR ECLIPSE
A total lunar eclipse is visible throughout North America on the evening of December 20/21. The following timetable is provided by Clark Planetarium in Salt Lake City.
Partial phase begins: 11:32pm MST on the 20th
Total phase begins: 12:40am MST on the 21st
Maximum eclipse: 1:18am MST
Total phase ends: 1:53am MST
Partial phase ends: 3:01am MST

Local Stargazing
Red Rock Astronomers offers telescope viewing before Moab’s Light Parade on Saturday, December 4. Look for them near the Moab Information Center at the corner of Main and Center. Sponsored by WabiSabi. All ages are welcome. For information call 259-4743 or 259-3313.
Last month Red Rock Astronomers hosted the Great World Wide Star Count at Old City Park. The GWWSC, sponsored by University Corporation for Atmospheric Research in Boulder, CO, seeks to promote interest in astronomy and to monitor the darkness of our night sky. Participants in the local star count detected 5th magnitude stars, despite partly cloudy skies. Visible stars range in magnitude from -1 to 6 (see Note following VISIBLE PLANETS). The quality of our night skies remains good when looking directly overhead, even though a significant light dome does arise above Moab and Spanish Valley. Outdoor lighting (commercial and residential) poses the greatest threat to maintaining our dark skies as a natural resource. Shields over the tops of outdoor lights direct the light downward where it is useful. Lights that radiate 360 degrees produce glare, waste energy, and reduce the quality of our dark skies. In past years, we have easily detected 6th magnitude stars on clear nights. It is our decisions that determine whether we retain this valuable resource.

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.

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.


VISIBLE PLANETS
Jupiter - Find Jupiter high in the southwestern sky at evening twilight. By month’s end it sets before midnight. On December 13 look for Jupiter’s bright yellow orb near the first quarter moon. Jupiter moves from Aquarius to Pisces this month. (Magnitude -2.3)

Saturn - The yellow planet rises in the eastern sky during the night and appears overhead in the morning twilight. A thin waning crescent moon rises with Saturn on December 1 and again on December 31 when Saturn appears above the moon and Spica (Virgo). Saturn is in Virgo throughout the month. (Magnitude +0.3)

Venus - Look in the morning sky a few hours before sunrise for the brightest of all our planets. On December 31 a waning crescent moon rises with Venus. Venus moves from Virgo to Libra this month. (Magnitude -4.4)

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.

MAJOR CONSTELLATIONS this MONTH

Overhead
Andromeda
Aries
Auriga
Pegasus
Perseus
Pisces
Triangulum

Northward
Cassiopeia
Cepheus
Draco
Ursa Major
Ursa Minor

Eastward
Canis Minor
Gemini
Orion
Taurus

Southward
Aquarius
Canis Major
Cetus





Westward
Cygnus
Lyra

Winter’s display of the Milky Way directs our view towards the outer edge of the galactic arms. Trace its path from west to east across the evening sky—Cygnus, Cepheus, Cassiopeia, Auriga, and on between Orion and Gemini, then between the two bright dog stars (Sirius and Procyon).

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.

 
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