|Events during December
|4th - Mercury passes through inferior conjunction.
10th - Total Lunar Eclipse - visible from eastern Europe, east Africa, Asia, Australia and the Pacific. Eastern Asia, Indonesia, Australia
and Japan are the best places for viewing this eclipse at a good altitude, near midnight.
22nd - Winter Solstice in the northern hemisphere, when the Sun reaches its most southerly point over the Tropic of Capricorn.
23rd - Mercury - at greatest western elongation (22║).
MOON: Full - 10th, New - 24th, Apogee - 405,415 kilometres - 6th, Perigee - 364,800 kilometres - 22nd.
Meteor Showers during December
The Geminids meteor shower lasts from the 7th to the 16th December,
peaking on the morning of the 14th.
The Geminids can be one of the best meteor showers of the year although un-favourable conditions pre-vail this year
due to a Full Moon on the 10th. The Geminids are slow meteors that create beautiful, some-times colourful, long arcs across the sky, many lasting a second or two.
This shower is seen to be intensifying every year. Originally observed at 20 to 60 meteors per hour, recent showers have seen 120-160 meteors
per hour under optimal conditions, around 2am to 3am local time. Geminids were first observed just 150 years ago, much more recently than other showers.
The Geminids originate from asteroid 3200 Phaethon. Together with the Quadrantids, they are the only major meteor showers not originating from a comet.
The best place to observe a meteor shower is somewhere dark, away from light pollution, and with the Moon out of the field of vision.
The less light visible, the more brilliant the meteor shower will be. The best way to observe meteors
is to lie outdoors in a recling chair or sun-lounger (easier for summer showers of course!). Try to take in as much of the sky as possible. When you see a meteor
mentally trace it backwards. After tracing back a couple, you will notice where their paths intersect at the radiant point.
Mercury passes through inferior conjunction
on December 4th and quickly moves out to the west of the Sun, reaching greatest western elongation
December 23rd. Consequently, the planet is visible as an early morning object from mid-December until the end of the year. From northern temperate latitudes,
Mercury will be seen low in the south-eastern sky at the beginning of twilight. It is at its brightest following greatest western elongation and, during the
last two weeks of December, it brightens from +0.2 to -0.4 magnitude.
The best times to observe Mercury in the northen hemisphere are when it is an evening star in the spring and a morning star in the autumn. In midsummer
the lighter skies make visibility difficult near the horizon.
Venus, at magnitude -4.0, is now a true Venusian spectacle in the early evening sky after sunset,
setting two hours after the Sun by the end of December. On 27th December the waxing crescent Moon will make a beautiful pairing with Venus in the evening twilight sky.
On the 8th June 2004, Venus was at inferior conjunction
and transited the sun. Transits of Venus are rare, taking place at greater
than 100 year intervals and usually in pairs. The last two transits of Venus were in 1874 and 1882. 2004's transit lasted 6 hours, the total event
visible from Europe as a small black disc crossing the lower part of the Sun from left to right. The next transit will be on 5th June 2012.
After that, transits of Venus won't occur again until 2117 and 2125.
Before and after inferior conjuction, when Venus is
the closest it comes to the Earth, are the times at which the planet is most brilliant and can be seen setting or rising
4 hours after or before the Sun.
Mars brightens further from +0.7 to +0.2 magnitude during December, heading towards
opposition in March 2012
. Remaining in Leo
, Mars rises in late evening by the end of the month
and is well placed for observation during the early morning hours.
There has been no opposition of Mars in 2011.
At opposition on the 28th August 2003, Mars was only 56 million kilometres from the Earth. It showed a
disc of 25.1 seconds of arc across which is almost as large as it can ever appear. Mars started 2003 at 310 million kilometres from
the earth at 4.5 seconds of arc and 1.6 magnitude. By opposition it brightened 50 times to reach -2.9 magnitude but faded to 0
magnitude by December. Even to the naked eye Mars was a striking object in the summer and autumn sky, easily identifiable by its
reddish hue in an area of sky poor in bright stars. Mars will not be as close again until 2018.
These favourable oppositions occur every 15 or 17 years but other oppositions occur at average intervals of 2 years 2 months during
which time the planet makes a complete circle of the Earth. In general Mars is observable every other year, being too close to the sun for favourable conditions
during other times. Brightness at opposition varies from -1.0 to -2.9 magnitude, and when furthest from the earth it fades to 1.7 magnitude. The planet can be
identified by its orange-red colour.
As in 2003, Mars comes nearest to the Earth at oppositions at the end of August. At these times it can be brighter than Jupiter,
although low in the sky in Aquarius for northern observors. In the northern hemisphere, the planet may be better seen at oppostions during autumn and winter months
when it is higher in the sky.
Jupiter is not long past opposition and is
still visible in the southern sky as soon as darkness falls, setting in the early morning hours.
Commencing December in the constellation of Aries, its
retrograde motion carries it into neighbouring Pisces. Jupiter reaches its 2nd stationary point
on December 26th and there-after resumes direct motion.
During December, magnitude fades from -2.8 to -2.6 as its distance from Earth increases. The waxing gibbous Moon lies just north of Jupiter on December 6th
making a striking pair in the evening sky.
After spending the past six years in the southern skies, Jupiter moved north of the celestial equator on February 5th 2011 to spend the next six years
in northern skies.
Varying from 603 (at its closest) to 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than
with Mars, from about -2.9 to -1.8 magnitude. Always a bright planet, Jupiter comes to opposition a month later each year, moving approximately from one zodiacal
constellation to the next.
The 4 largest of Jupiter┤s 60+ moons are easily visible through binoculars or a small telescope, ranging from 4.6 to 5.6 in magnitude. The innermost,
Io, takes 1.8 days to orbit the planet making its motion easily detectable within a few minutes.
Saturn passed through superior conjunction
in mid-October and, as the planet pulls away from the Sun, is becoming more visible. At magnitude +0.7, it can be seen in
Virgo moving eastwards until before dawn. The apparent tilt of the rings, as viewed from Earth, has increased to over 14║ by the end of 2011.
Saturn moves more slowly than Jupiter and can remain in the same constellation for several years. The brightness of the planet depends on the
aspect of its rings, as well as its distance from Earth and the Sun.
The planet crossed the equator into the northern hemisphere in 1996 where it remained until 2010 with the southern side of the ring system
facing Earth. Because of its distance, its brightness varies little between opposition and conjunction but is affected by the huge ring system. Seen edge on the
rings contribute little or no light.
Every 15 years the plane of Saturn's rings passes through the Sun, illuminating first the north and then the south side. For a few days the
rings are edge on to the Sun. About the same time the Earth passes through the ring plane and, depending on the Earth's position, this may happen just once or 3 times.
During 1995/96 there was a triple crossing and the next will be 2038/39. The last single crossing was in 2009 and the next will be in 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
Uranus remains in Pisces with a magnitude of +5.7. Although
barely visible to the naked eye, it is easily located with binoculars.
Brightness varies only slightly, reaching a maximum of +5.6 magnitude at opposition. Although this is bright enough to see with the naked eye, identifying it against
the stars can be difficult. At closest approach, Uranus is 2,856 million kilometres (1,775 million miles) from Earth.
Neptune is a morning object in Aquarius
visible in binoculars or a small telescope.
Neptune has an average magnitude of 7.9 which varies little with changing distance. At its closest,
Neptune is 4,341 million kilometres (2,697 million miles) from Earth.
No longer an offical planet and never brighter than +13 magnitude, Pluto is only visible through powerful telescopes.
First quarter: 2nd
Full moon: 10th
Last quarter: 18th
New moon: 25th