|Events during December
This month the apolypitcal forces foretold by Nostradamus and the Mayans come to pass with the precession of the Equinoxes on the 21st December 2012
3rd: JUPITER is at opposition in Taurus
4th: MERCURY is at greatest western elongation (21°)
13th-14th: GEMINIDS METEOR SHOWER peaks (duration 7th to 16th December)
21st: WINTER SOLSTICE in the northern hemisphere, when the Sun reaches its most southerly point (the lowest viewed from the north) over the Tropic
of Capricorn giving us the shortest days and longest nights.
6th: Last quarter
9th: the crescent Moon lies near Spica, (the brightest star in Virgo at magnitude +0.95)
10th: the crescent Moon is to the right of Saturn in the morning sky
11th: in the southeast sky, at 7:30h just before dawn, the crescent Moon forms a spectacular pairing with Venus, while Mercury lies just to the lower left and Saturn higher on the right.
12th: Perigee at 357,075km
15th: in the evening sky the crescent Moon lies above Mars
20th: First quarter
25th: Apogee at 406,100km + the Moon lies close to Jupiter with Aldebaran (a giant red star, the brightest in Taurus, at magnitude +0.85) to the lower left
The GEMINIDS Meteor Shower, duration from 7th to 16th December, are currently the most active of the regular annual showers with rates outstripping even
those of the August Perseids for a 24-hour period around their 13th-14th maximum – a real treat for observers prepared to brave chillier nights. In recent years
the zenithal hourly rate has peaked at 120-140 meteors per hour. From a lunar point of view, with a new Moon on the 13th, this year conditions are ideal with zero
interference from moonlight. Geminid meteor activity is expected to peak this year at about 20:00h Spanish time on Thursday 13th December with good rates from
before dawn on the 13th through to early morning hours on the 14th. The larger number of brightest Geminid meteors and fireballs usually occur after maximum peak,
therefore late evening and early morning of December 13th/14th.
Geminid meteors enter Earthīs atmosphere at a relatively slow 35 km/s and tend to last longer than most in luminous flight. Unlike an average Persied or Orionid
meteor, which last a few tenths of a second, Geminids are often longer than a second and sometimes fragment showing a chain of light. Their low speed and abundance
of bright meteors makes the Geminids a prime target for digital astrophotography.
JUPITER, at opposition, is at its brightest this month. Opposition is a term that literally means a planet is opposite the Sun in the sky as viewed from
Earth. The Moon is at opposition when full. A planet at opposition is at its closest approach to the Earth and is best suitable for observing although, at a distance
of 609 million kilometres (378 million miles), “close” is a relative term.
With a diameter of 143,000 kilometres, Jupiter is so vast it could contain 1,300 Earths and,
as itīs composed almost entirely of gas, is efficient at reflecting sunlight. Although so huge, Jupiter spins faster than any other planet in our Solar System,
rotating every 9 hours 55 minutes.
Jupiter has a family of more than 60 moons, the four largest of which are visible to the naked eye or through binoculars held rigidly.
Galileo first saw these “Galilean moons”, worlds in their own right, in January 1610. Io, At a mean distance of 421,600 kilometres, orbits Jupiter closer than our Moon
to Earth. It is the most volcanic body known in the solar system with lava lakes and flows, and sulphurous geysers reaching 500 kilometres high. Europa, with a
diameter of 3,130 kilometres – about the same as Earth`s Moon, is the smallest of the Galilean satellites. It orbits Jupiter at a mean distance of 670,900 kilometres
and appears to harbour a global ocean of liquid water, hidden under a frozen surface, where alien fish may swim.Ganymede is Jupiter`s largest moon and, with a diameter
of 5,262 kilometres, is also the largest in the solar system. It orbits its parent planet at a mean distance of 1,070,000 kilometres. Callisto, the second largest moon
about the same size as Mercury, orbits Jupiter at a mean distance of 1,883,000 kilometres.
MERCURY reaches greatest western elongation
(21š) on 4th December and,
from the tropics and northern temperate latitudes, is visible as a morning object until the third week of the month with brightness increasing slightly from -0.2 to -0.5
magnitude. From the northern hemisphere this is the most interesting morning apparition of the year, due to the proximity of Venus during the first two weeks of the month.
The brilliant Venus is a useful guide to locating a much fainter Mercury.
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, remaining at magnitude -4.0, is visible in the eastern sky before dawn. At the beginning of
December, Venus rises two and a half hours before the Sun from northern temperate latitudes, less from further south, but by the end of 2012 it rises just one and a
half hours before the Sun from all latitudes as its elongation from the Sun decreases. The planetīs phase increases
from 88% to 94% during December.
On the 8th June 2004 and 5th/6th June 2012, 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. Prior to that, the last two transits of Venus were in 1874 and 1882. Transits of Venus won't occur again until 2117
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, remaining at magnitude +1.2, moves from Sagittarius
into Capricorn during December. The planet sets under two hours after the Sun and continues to be rather low in the
south-western sky at dusk.
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 at opposition on 3rd December and
therefore at its brightest this month and visible throughout the night. The good news for us is the planetīs northerly declination allows a great view for
observers in the northern hemisphere. Jupiter is moving retrograde in
Taurus and is in line with the northern arm of the V-shaped Hyades cluster at opposition.
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 Jupiterīs 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, at magnitude +0.6, moves eastwards from Virgo
into neighbouring Libra this month and continues to be visible in the south-eastern sky before dawn. The tilt of the rings,
as viewed from Earth, has increased to almost 19° by the end of the year.
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, at magnitude +5.8 in Pisces, is visible with
sharp eyesight or binoculars, setting around 1:30h.
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)
NEPTUNE, the most distant planet at magnitude +7.9 in Aquarius,
can be revealed through a telescope and sets about 10:30h.
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.
Last quarter: 6th
New moon: 13th
First quarter: 20th
Full moon: 28th