SkyEye

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

December 2012

The Calendar

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	Sat
2	Sun
3	Mon	Jupiter at opposition
4	Tue	Mercury at greatest elongation west
5	Wed
6	Thu	The Last Quarter Moon leaves the first half of the night dark to observe the southern hemisphere's Phoenicids and Puppid-Velids.
7	Fri
8	Sat
9	Sun	4 Vesta at opposition
9	Sun	Moon occults Spica: visible from southern South America from about 11:00 UT.
10	Mon
11	Tue
12	Wed	Moon occults Mercury: visible from Antarctica.
12	Wed	Moon at perigee only nine hours before New phase, leading to high tides.
13	Thu	The New Moon provides perfect observing condition for the ever-reliable Geminids (theoretical peak activity: 23:30).
14	Fri
15	Sat
16	Sun
17	Mon
18	Tue	1 Ceres at opposition
19	Wed
20	Thu	First Quarter Moon
21	Fri	Solstice on Earth
22	Sat	The waxing gibbous Moon means dark skies after around 02:00 local time in the northern hemisphere, allowing for good observations of the Ursids (theoretical peak activity: several predictions ranging from 03:00 UT to 08:00 UT).
23	Sun
24	Mon
25	Tue	Moon at apogee
25	Tue	Moon occults Jupiter: visible from central South America and southwestern Africa from 22:20 UT.
26	Wed	Uranus at east quadrature
27	Thu
28	Fri	Full Moon
29	Sat
30	Sun
31	Mon

Coming up next month...

The Quadrantids will be seriously compromised by moonlight when they peak on 3 January.

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: Libra » Scorpius » Ophiuchus » Sagittarius
Emerging from the solar glare in the morning sky, the closest planet to the Sun attains greatest elongation west on the fourth day of the month. It also undergoes a barely visible occultation by the Moon on 12 December. This elusive planet is best viewed from the northern hemisphere this month and remains on display until the new year.
Venus: Libra » Scorpius
The 'morning star' is quite low in the east before sunrise. It appears to be maintaining altitude from southern latitudes but is sinking quickly from the vantage point of the northern hemisphere.
Mars: Sagittarius » Capricornus
The red planet sets soon after the Sun.
4 Vesta: Taurus
The brightest of the asteroids is at opposition on 9 December. It is just barely visible to the naked eye under very dark skies.
1 Ceres: Gemini » Taurus
The largest object in the asteroid belt is at opposition on 18 December. Binoculars will be necessary to observe this seventh-magnitude object in the constellation of Taurus.
Jupiter: Taurus
Blazing away at nearly third magnitude, the largest planet is at opposition on 3 December and is visible all night. Look for an occultation by the Moon on 25 December.
Saturn: Virgo » Libra
The ringed planet is on view from the early hours of the morning.
Uranus: Pisces
Uranus reaches east quadrature on 26 December and sets around midnight.
Neptune: Aquarius
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.

The SkyEye banner features the supernova remnant known as the Crab Nebula. Six light years wide and 6500 light years distant, this expanding nebula is the shattered remains of a star that blew up nearly a thousand years ago. At its heart beats a pulsar, a neutron star which spins at the incredible rate of 30 times per second. The supernova explosion which produced this object was observed in 1054 in China, Japan and Arabia. It was also seen in North America by the Anasazi people who lived in what is now New Mexico and who depicted it in a petroglpyh. This image is a composite assembled from 24 individual exposures taken by the Hubble Space Telescope in October 1999, January 2000 and December 2000, and is courtesy of NASA, ESA, Jeff Hester and Allison Loll (Arizona State University). The colours represent different elements which were expelled during the explosion: neutral oxygen (blue), doubly-ionised oxygen (red) and singly-ionised sulphur (green). These elements will find their way into the next generation of stars and planets (and extra-terrestrial life?).