Graphic
Mercury rises nearly 2h before the Sun on the 1st, a bright -0.6 magnitude, but sinks back towards the horizon during the month, though brightening slowly. Very close to Mars and Jupiter over the 8th-12th (see below). Venus reappears low in the southwestern sky after sunset setting only minutes after the Sun on the 1st but more than an hour after by the 31st. A brilliant -3.8 magnitude it should become visible in bright twilight after mid-December. Mars rises about 06h 30m throughout the month and will be in a dark sky but low down from mid-month. Mars above the Moon on the 19th.
Jupiter is in Libra moving through Scorpius into Ophiuchus and rising about 07h on the 1st and 05h 30m by the 31st. Saturn is 0.3 magnitude and in Leo, a little to the west of the bright star Regulus. It is stationary on the 6th and then moves slowly westwards against the stars (retrogrades) as it approaches opposition in February. Moon near by on the 9th.
Uranus is in Aquarius setting about 21h 30m by the 31st. Moon near by on the 25th. Neptune is in Capricornus setting soon after 19h by the 31st. Moon near by on the 23rd.
The Moon: full 5d 00h, last quarter 12d 15h, new 20d 14h, first quarter 27d 15h. The full Moon will rise well round to the northeast and be above the horizon for over 17h. Moon near Spica on the 15th.
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The Earth: the winter solstice, when the Sun reaches its most southerly point over the Tropic of Capricorn, is on 22d 00h.
London area, sunset: 1 Dec 15h 50m, 31 Dec 16h 00m, sunrise: 07h 45m, 08h 08m. Nautical twilight ends: 1 Dec 17h 15m 31 Dec 17h 20m, begins: 06h 25m, 06h 45m. Edinburgh area, sunset: 1 Dec 15h 42m, 31 Dec 15h 45m, sunrise: 08h 20m, 08h 44m. Nautical twilight ends: 1 Dec 17h 16m, 31 Dec 17h 22m, begins: 06h 45m, 07h 08m.
In the dawn sky about the 10th three planets will come close together, Mercury (-0.6 magnitude), Mars (+1.5 mag) and Jupiter (-1.7 mag). Although low in the brightening dawn sky, they should be visible with the naked eye given a clear sky and low skyline though binoculars will be a help, especially for Mars. On the 7th Mercury will be above fainter Mars, with Mars above the brightest planet Jupiter. By the 10th all three planets will lie within a circle about twice the diameter of the full Moon or 1° across. The star close to Mercury and Jupiter is 2.6 mag Beta Scorpii which may be hard to see. By the 13th Jupiter will be above Mars, with Mars above Mercury. It is unusual to have three major planets so close together.
The Geminids meteor shower reaches maximum activity about 05h on the morning of the 14th. The Geminids is the richest and most reliable of the annual showers and on the night of the 13th-14th 60 or more meteors per hour are likely. The radiant area is near Castor (see chart), low in the east in the early evening but high in the south after midnight. The Moon will be past last quarter and rises after 01h so should not interfere too much. Some Leonid meteors were seen about the predicted time on November 19 but first reports suggest not a large number.
Comet 2006 M4 (Swan) became a naked eye object when seen in a dark sky. It underwent two outbursts in October becoming brighter than 5th magnitude for a few days with a faint tail 3° long. In December it will be a rather faint telescopic object.
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The shortest day at our latitude is on the day of the winter solstice, about the December 21, but the earliest sunset and latest sunrise occur ten days before and after this date (about December 13 and January 2). These dates are for Greenwich but vary by a few days with latitude: in northern Scotland the earliest sunset is about the 16th. The Sun does not move eastwards at a uniform rate, so successive noons as shown by a sundial are not exactly 24h apart. This arises because the Sun moves along the ecliptic not the equator so it runs slow near the equinoxes and fast near the solstices. It is complicated by the eccentricity of the Earth’s orbit which makes the Sun appear to move faster near perihelion (about January 4) and slower near aphelion (about July 3).
Astronomers invented a ficticious “mean” or average Sun which is assumed to move at a uniform rate along the equator and our clocks are related to this mean time. Four times a year the true and mean Suns coincide, about April 15, June 13, September 1 and December 25, when a sundial shows the Sun due south at mean noon. The greatest differences occur about February 11 when the Sun transits the meridian (is due south) at 12h 14m by our clocks while about November 4 it transits early, 16 minutes before mean noon.
The diagram shows the brighter stars that will be above the horizon in the latitude of London at 23h (11pm) at the beginning, 22h (10pm) in the middle, and 21h (9pm) at the end of the month, local mean time. At places away from the Greenwich meridian the Greenwich times at which the diagram applies are later than the above by one hour for each 15 deg west of Greenwich and earlier by a like amount if the place be east. The map should be turned so that the horizon the observer is facing (shown by the words around the circle) is at the bottom, the zenith being at the centre. Greenwich Mean Time, known to astronomers as Universal Time and expressed in 24-hour notation, is used in the accompanying notes unless otherwise stated.