Earth--Day and Night Regions

Earth--Day and Night Regions

Planetary Positions

Sunday, December 25, 2011

The Night Sky This Month--December

The Night Sky This Month (December 2011)




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Key Stars



For observers at mid-northern latitudes, the Pleiades star cluster is

due south around 10 P.M. local time. Above it is Perseus, flanked by

Auriga and Cassiopeia. Orion can be found above the southeastern

horizon, and between it and the celestial pole glitters Capella. High

in the east are Castor and Pollux, the brightest stars of Gemini, and

below them Leo the Lion is rising. In the southwest is the Square of

Pegasus and Vega shines low above the northwestern horizon.



The Planets



Mercury



Mercury moves to December's morning sky, but will be hard to spot for

the first half of the month. By the end of the month, however, it will

rise almost ninety minutes before the Sun and will be easily

identified sitting 10 degrees to the lower left of the 1st-magnitude

star Antares (Alpha Scorpii).



Venus



Until late May 2012, Venus will appear as a brilliant yellow star in

the evening sky, right after sunset. This month the planet is located

15 degrees above the southwestern horizon half an hour after sundown,

and it remains on view until after 6 P.M. local time.



Mars



Mars pokes above the eastern horizon around midnight local time and

is well up in the south before dawn. The planet is on its way to

opposition next March, when it will be at its closest approach to

Earth and will reach a width of 14". Right now, the disk is less than

9"-wide, too small to show features in most instruments.



Jupiter



Jupiter reached opposition to the Sun in late October, when it was

closest to Earth and at its largest and brightest. Although Jupiter

is now slowly receding from our home planet, it remains visible well

after midnight and looks stunning through a telescope. The gas giant

shines at magnitude -2.7 and lies in a star-barren region near the

border between Aries and Pisces.



Saturn



Throughout December, Saturn is low in the southeast as dawn begins,

but gets a little higher every morning. The ringed planet resides

among the background stars of Virgo the Maiden and remains within 5

degrees of the blue-white star Spica all month. Through a telescope,

Saturn sports an angular size of 16", while the rings span 37".



Uranus



Uranus lies in the same binocular field of view as Lambda Piscium,

the star that forms the southeast corner of the "Circlet" in Pisces,

and is itself an easy binocular target. The planet glows at magnitude

+5.8 and looks just like a star of that brightness. A telescope easily

reveals its 3.4"-diameter disk, which has a distinct blue-green color.



Neptune



Seek out Neptune in western Aquarius, 1.5 degrees northwest of the

4th-magnitude star Iota Aquarii. The distant world lies 2.8 billion

miles from Earth and glows dimly at magnitude +7.9. A 4-inch diameter

telescope is probably the minimum required to see the planet and

resolve its disk, only 2.4" across.



Pluto



The dwarf planet is too deep in the evening twilight and cannot be

observed until mid-February 2012, when it will reappear in the

morning sky.



Bright Asteroids



Vesta



8th-magnitude Vesta is an easy find in small telescopes. Look for it

just after dusk, when Aquarius the Water-Bearer - the constellation

through which the asteroid tracks - is highest above the southern

horizon.



Amphitrite



This space rock wends its way through the rather faint constellation

Aries the Ram, which is nearly overhead for observers at mid-northern

latitudes around 8 P.M. local time. The asteroid glows at magnitude

+9.6 - outside the range of binoculars from a suburban backyard, but

well within the reach of a 3-inch scope.



Bright Comets



C/2009 P1 Garradd



Comet Garradd can be found among the background stars of the

constellation Hercules, a few degrees east of Delta Herculis, and

according to recent reports, it should glow at 7th magnitude. This

"dirty ice ball" appears as a bright, round fuzz ball roughly 10'

across, with little hint of a tail. The key to finding C/2009 P1

Garradd is to start half an hour after sunset from a site that has an

unobstructed view of the western horizon.



C/2010 G2 Hill



This comet was discovered on April 10, 2010, in the course of the

Catalina Sky Survey, and astronomers expect it to glow around 10th

magnitude throughout December. Search for it around 10 P.M. local

time, when it lies high in the south within the borders of the

constellation Taurus.



Meteor Showers



The Geminids are active from December 7 to 17th and peak very quickly

on the night of December 13 - 14. Most activity occurs after midnight

on the 14th, when as many as one hundred slow, graceful Geminids

might be seen per hour under ideal conditions. This year, however,

the Moon rises at mid-evening and shines all the way until daybreak,

so bright moonlight will wash out most meteors.



The Ursid shower is active from December 17 to December 26, and peaks

on the morning of December 23. The Moon is New on the 24th - which

means no moonlight, dark skies and perfect observing conditions! The

radiant lies near the bright star Kochab (Beta Ursae Minoris), which

appears below the Pole Star in the evening and above it before dawn.

The radiant is circumpolar from most of the Northern Hemisphere, so

viewing can last all night.



Sky Events



December 1 - Venus is at greatest eastern elongation, 27.3 degrees

east of the Sun in the evening sky.



December 2 - First Quarter Moon at 4:52 A.M. EST.



December 4 - Mercury is in inferior conjunction with the Sun.



December 5 - The Moon is at apogee, the point in its orbit when it is

farthest from Earth.



December 8 - The Moon is 3.1 degrees south of the Pleiades at 8:26

P.M. EST.



December 10 - Full Moon at 9:37 A.M. EST. A total lunar eclipse is

visible from western North America and across the Pacific Ocean to

Australia and Asia.



December 14 - The Geminid meteor shower is at peak activity.



December 17 - Last Quarter Moon at 7:48 P.M. EST.



December 21 - The Moon is at perigee, the point in its orbit when it

is nearest to Earth.



December 22 - The winter solstice occurs at 12:30 A.M. EST. Mercury

is at greatest western elongation, 21.8 degrees west of the Sun in

the morning sky.



December 23 - The Ursid meteor shower is at peak activity.



December 24 - Mercury is 6.6 degrees north of Antares (Alpha Scorpii)

at 5:36 A.M. EST. New Moon at 1:06 P.M. EST.



December 27 - The Moon is 6.7 degrees north of Venus at 5:52 A.M.

EST.



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