During December Mercury is at inferior conjunction on the 10th, the Geminids meteor
shower is from the 12th-14th, Winter Solstice is on the 21st and there is a full moon on the 26th.
The Geminids Meteor Shower
The Geminids meteor shower lasts from the 9th to the 19th December with maximum meteors from the 12th to the 14th. Favourable
conditions exist this year with a dark moon new on the 12th. Predictions are for an average rate of 100 meteors per hour at peak time.
The point from where the Geminid meteors appear to radiate is located within the constellation Gemini and is referred to
as the radiant. Shown as the red star on the chart, the radiant is located in the northern portion of the constellation
near Gemini's two brightest stars, Castor and Pollux. These meteors tend to move moderately fast, when compared to other
meteor showers, and Geminids tend to be rather bright.
To best observe the Geminids lie outside in a reclining chair. The Geminid radiant is above the horizon for nearly all
hours of darkness and the optimum observing point shifts throughout the night. Early in the evening the best observing
position is to point your feet north, west, or southward and look straight up. Late in the evening your orientation
could remain unchanged, but you should shift the center of your gaze to about 45 degrees above the horizon. By about 2.00h
you can point your feet in any direction, with your gaze centered about 45 degrees above the horizon. By late morning, the
best vantage point would be to point your feet towards the north, east, or south and set your gaze to a point again about
45 degrees above the horizon.
The Geminids are famed for meteors known as Earthgrazers. Soon after sunset these can be seen flying over the horizon
parallel to the atmosphere. They are long, slow-moving, vivid and bright with colourful tails. Last year we were enjoying
dinner by Lake Vinuela when one appeared to fly the length of the lake. It was truly spectacular.
The first Geminid shower appeared in 1862 and scientists are still in dispute as to whether they originate from a comet,
as do other meteor showers, or whether they eminate from an asteroid.
||Mercury is at inferior conjunction on the 10th December and at greatest western
elongation of 22 degrees on the 29th. By the end of the month Mercury rises 2 hours before the sun and, at -0.2 magnitude,
will be visible low in the southeast before sunrise. Venus is closeby on the 29th.
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 is now moving closer to the sun and can be seen in the southeast rising
about 7.30h by the end of December. Mars is closeby on the 5th and the moon on the 10th.
On the 8th June, 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 passes from Libra to Scorpio in late December and is low in the southeast
sky before sunrise. Venus is closeby on the 5th and the moon on the 10th.
At opposition on the 28th August last year, 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 remains in Virgo at -1.9 magnitude rising by 2.00h by the end of
December. The moon is closeby on the 7th.
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 is in Gemini throughout 2004. At -0.3 magnitude the planet rises soon
after sunset by the end of December. The moon is closeby on the 1st and 27th.
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 remains in Aquarius throughout 2004. By the end of December Uranus will
set by 22.00h. The moon is closeby on the 16th.
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 remains in Capricorn throughout 2004. At 8.0 magnitude Neptune is
sets by 20.00h by the end of December and has the moon closeby on the 15th.
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.|
||Last quarter: 5th at 02.00h
New moon: 12th at 02.00h
First quarter: 18th at 18.00h
Full moon: 26th at 16.00h