SkyEye

Welcome to SkyEye, your guide to this month's celestial events.

December 2010

All times and dates are given in Universal Time (UT).
Nightly darkness estimates are calculated for 45° N and 30° S.
Like total solar eclipses, lunar occultation events can be seen only from limited regions on Earth (and sometimes not at all if the occultation takes place during daylight hours). However, the Moon will appear close in the sky to its "target" for some hours either side of the actual occultation, regardless of where you are.

Date		Event
1	Wed	Mercury at greatest elongation east
2	Thu
3	Fri
4	Sat
5	Sun	New Moon
6	Mon	Moonless skies favour this year's return of the Phoenicids (theoretical peak activity: from 15:30 UT).
6	Mon	Moon occults Mars: visible from about 22:30 UT in Cuba, Manitoba, and central and southeastern United States.
7	Tue	Similarly, observers of the poorly-studied Puppid-Velids enjoy dark skies.
8	Wed
9	Thu
10	Fri
11	Sat
12	Sun
13	Mon	First Quarter Moon at apogee
14	Tue	The waxing gibbous Moon leaves the second half of the night dark for observing the ever-reliable Geminids (theoretical peak activity: from 11:00 UT).
15	Wed
16	Thu	Jupiter at east quadrature
17	Fri
18	Sat	Uranus at east quadrature
19	Sun
20	Mon	Mercury at inferior conjunction
21	Tue	Full Moon
		A total lunar eclipse is visible from the Americas, most of the Pacific Ocean, most of Australasia and Asia, most of Europe, western Africa and much of the Atlantic Ocean.
		Solstice
22	Wed	Impossibly light skies obliterate the Ursids this year.
23	Thu
24	Fri
25	Sat	Perigee
26	Sun
27	Mon
28	Tue	Last Quarter Moon
29	Wed
30	Thu
31	Fri

The Solar System

The word planet is derived from the Greek word for "wanderer." Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies including comets, are not so constrained, often moving far above or below the ecliptic.

Sun: Ophiuchus » Sagittarius
Although Ophiuchus is not a member of the zodiac, the ecliptic passes through it. A solstice occurs on Earth on 21 December The word solstice means "sun stands still" so that on this day, the solar declination reaches an extreme. In this case, the Sun appears directly over the Tropic of Capricorn in the southern hemisphere. From now until the solstice in June, days will be getting shorter in the southern hemisphere and longer in the northern hemisphere.
Mercury: Sagittarius » Ophiuchus
Greatest elongation east on the first day of the month sends this tiny planet back toward the western horizon where it is lost in solar glare by mid-month. Inferior conjunction is on 20 December.
Venus: Virgo » Libra
The "morning star" continues to rise higher in the east ahead of the Sun. This turns into a slight descent for northern hemisphere observers by the end of the month.
Mars: Ophiuchus » Sagittarius
The red planet is getting increasingly difficult to see low in the west at sunset.
Jupiter: Aquarius » Pisces
East quadrature occurs on 16 December, making this an excellent time to observe telescopically the interplay of the planet, the Galilean satellites and their shadows. The king of the planets sets around midnight.
Saturn: Virgo
The ringed planet rises shortly after midnight.
Uranus: Pisces
Like its much brighter neighbour, Uranus reaches east quadrature this month (two days after Jupiter) and sets around midnight. These two planets have the last of their three encounters next month.
Neptune: Capricornus
A small telescope is necessary to view the most distant planet in the solar system. It sets mid-evening.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union (IAU) recognises 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies or some of the closest stars to the Sun.

Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if summer (daylight savings) time is in effect.

Local Time	Northern Hemisphere	Southern Hemisphere
1730 hours (1830 hours summer time)	45° N	30° S
1930 hours (2030 hours summer time)	45° N	30° S
2130 hours (2230 hours summer time)	45° N	30° S
2330 hours (0030 hours summer time)	45° N	30° S
0130 hours (0230 hours summer time)	45° N	30° S
0330 hours (0430 hours summer time)	45° N	30° S
0530 hours (0630 hours summer time)	45° N	30° S

For More Information...

Consult our online glossary for non-technical explanations of many of the astronomical terms used in these pages.
Blue moons, eclipses, the dates of Easter and much more can be found at the Interactive Astronomy Pages.
For more information about the objects and events described in SkyEye, visit these astronomy-related sites.

Credits

Much of this information can be found in this month's issue of your favourite amateur astronomy magazine available in your local bookshop. Another excellent source is the current edition of the Astronomical Calendar by Guy Ottewell and published by the Universal Workshop at Furman University.

The SkyEye banner features a collision of galaxy clusters and is courtesy of NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara) and S. Allen (Stanford University). When MACS J0025.4-1222 was formed, gravity caused the ordinary matter in the colliding galaxy clusters to slow down whereas the dark matter, which at best interacts only weakly with itself, continued on its original course. Thus, this object provides both confirmation of the existence of dark matter and a further understanding of its properties. This image is a composite of Hubble Space Telescope and Chandra X-ray Observatory data where dark matter is coloured blue (mapped by Hubble using gravitational lensing techniques) and ordinary matter is coloured pink (mapped by Chandra detecting X-rays from gas heated by the collision).