|Special Events in December
During December there is a new Moon on the 1st and again on the 31st, Mars is stationary on the 10th,
Mercury is at greatest western elongation on the 12th, the Geminids meteor shower is from the 12th to the 14th
(unfavourable conditions for visibility with a nearly full Moon), there is a full Moon on the 15th, the Winter Solstice is
on the 21st at 20.00h and Venus is stationary on the 23rd.
||Mercury is at –0.4 magnitude rising almost 2 hours before the Sun at about
the time of greatest western elongation of 21º on the 12th December. Mercury is visible low in the southeast at dawn.
The best times to observe Mercury 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 has been hanging as an incredibly brilliant object, following the
setting sun, for the last two months. During December, on the 7th, Venus reaches greatest brilliancy of –4.7 magnitude,
setting two and a half hours after the Sun. The planet is stationary on the 23rd with the Moon closeby on the 4th.
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. June's transit
began at 7.20h and lasted 6 hours until 13.20h, 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 in late 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. The dates of the next two inferior conjunctions are October 28th 2010 and October 26th 2018.
||Mars is stationary on the 10th, thereafter resuming direct motion against the
background of stars. Fading from the beautiful October and November display (reaching –2.3 mag) to –0.8 magnitude, by the
end of 2005 Mars sets about 04.30h. The Moon is closeby on the 11th and 12th.
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 for another 15 years.
These favourable oppositions occur every 15 years but other oppositions occur at average intervals of 2 years 2 months. 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.
||Jupiter, remaining in Virgo, slightly increases in magnitude to –1.8 and rises
as Mars sets at about 04.30h by the end of 2005. The Moon is closeby and below on the 27th.
Being 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than with Mars, from about -2.8 to -1.8 magnitude.
The 4 largest moons of Jupiter are easily visible through 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, remaining in Cancer, also increases slightly in magnitude to 0.0 and
rises about 19.30h by the end of 2005. The Moon is closeby and above on the 19th.
Saturn crossed the equator into the northern hemisphere in 1996 where it will remain until 2010 with the southern side of the ring system facing the 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 next single crossings will be in 2009 and 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
||Uranus, remaining in Aquarius, sets about 22.00h by the end of 2005. The Moon
is closeby on the 7th.
Brightness varies slightly reaching 5.6 magnitude at opposition. This is bright enough to see with the naked eye but identifying it against the stars is difficult.
||Neptune, remaining in Capricorn, sets about 20.00h by the end of 2005. The Moon
is closeby on the 6th.
Neptune has an average magnitude of 7.9 which varies little with changing distance.
||Never brighter than 13 magnitude, Pluto is only visible through powerful telescopes and we will therefore not be reporting on its position in the sky.|
||New moon: 1st and 31st
Full moon: 15th