SkyEye

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

December 2009

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	Tue	Moon occults the Pleiades: visible from about 1130 UT in southeastern Asia, the Philippine Sea and Hawaii.
2	Wed	Full Moon
3	Thu
4	Fri	Moon at perigee
5	Sat
6	Sun	The waning gibbous Moon interferes somewhat with the Phoenicids.
7	Mon	Viewing of the Puppid-Velids is similarly disturbed by moonlight.
8	Tue
9	Wed	Last Quarter Moon
10	Thu
11	Fri
12	Sat
13	Sun
14	Mon	The ever reliable Geminids should peak in dark skies early in the morning.
14	Mon	Uranus at east quadrature
15	Tue	Moon occults Antares: too close to the Sun to observe.
16	Wed	New Moon
17	Thu
18	Fri	Mercury at greatest elongation east
19	Sat
20	Sun	Moon at apogee
21	Mon	Solstice on Earth
22	Tue	The Ursids also benefit from dark skies this year.
23	Wed
24	Thu	First Quarter Moon
25	Fri	Saturn at west quadrature
26	Sat
27	Sun
28	Mon	Moon occults the Pleiades: visible from about 2300 UT in the Bahamas, northern South America and northwestern Africa.
29	Tue
30	Wed
31	Thu	The second Full Moon in a month is popularly known as a Blue Moon.
31	Thu	As if this isn't enough, a partial lunar eclipse also occurs tonight.

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 hemisphereand longer in the northern hemisphere.
Mercury: Ophiuchus -> Sagittarius
Never very high above the horizon after sunset, Mercury gives southern hemisphere observers the best views this month. This tiny planet heads back towards the Sun around about greatest elongation east on 18 December.
Venus: Libra -> Scorpius -> Ophiuchus -> Sagittarius
The "morning star" is very low in the east, rising not long before the Sun.
Mars: Leo
With opposition next month, Mars rises mid-evening, thereby being visible most of the night.
Jupiter: Capricornus
Jupiter has its third close encounter of the year with Neptune. Look for them in the west since they both set by mid-evening.
Saturn: Virgo
West quadrature occurs on 25 December. Look for the shadow of the rings on the planet's disc.
Uranus: Aquarius
At east quadrature on 14 December, Uranus now sets before midnight, just as Saturn rises.
Neptune: Capricornus
Although Neptune is very close to Jupiter late this month, a small telescope is necessary to spot it.

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 view of Saturn from its satellite Iapetus and is courtesy of NASA/JPL/Space Science Institute. Of all the major satellites of Saturn, Iapetus is the only one with a significant orbital inclination. Thus, whilst the rings appear nearly edge-on from all of the other major satellites, from Iapetus they are usually seen at a tilt. This image was taken during the Cassini-Huygens mission on 10 September 2007 and consists of 15 red, green and blue spectral filter images.