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Northern Hemisphere – December 2012
Ian Morison tells us what we can see in the northern hemisphere night sky during December
The constellations of Cygnus, Lyra and Aquila are in the west after sunset.
Taurus, Orion, Gemini and Canis Major rise in the east as the evening progresses.
To the south is the Square of Pegasus, containing around 8 visible stars if your eyes are
sensitive enough.
You can star-hop from the Square to the Andromeda Galaxy and may also see M33, the
Triangulum Galaxy.
The Pleiades and Hyades star clusters are in Taurus, with the planet Jupiter between them.
The bright star Aldebaran appears to be within Hyades, but is actually nearer to us.
Below Taurus is Orion, with the Orion Nebula visible as a fuzzy glow beneath the
Hunter's Belt.
Below the bright star Sirius, in Canis Major, is the open cluster M41. Most of its stars are
young and blue, but there is a red giant at its centre.
The Planets – December 2012
Jupiter rises at sunset at the beginning of the month and is visible
throughout the night as it reaches opposition (opposite the Sun in the sky)
during December. Shining at magnitude -2.8, it reaches 60 degrees' elevation
in Taurus in the south, helping us to see it with little atmospheric
interference. It is 5 degrees to the upper left of the star Aldebaran at the start
of December, moving westwards towards the Pleiades in its retrograde
motion during the month. With an angular size of around 48", plenty of
detail can be seen using a small telescope, especially on a night when the
Earth's atmosphere is still.
Saturn rises around 04:00 UT (Universal Time) at the beginning of the
month and about 02:30 at the end. Its brightness rises from +0.7 to +0.6
during December, while its angular diameter increases from 15.7 to 16.1".
Its rings now cover around twice that diameter as they have now opened out
to around 18-19 degrees from the line of sight, the greatest angle for six
years. With a small telescope, you can see Saturn's southern hemisphere, the
gap between its brightest rings and some of its moons.
Mercury reaches greatest western elongation (its furthest from the Sun in
the sky) on the 4th, being around 20 degrees from the Sun, and on that day
rises two hours before the Sun, near to Venus. It remains at magnitude -0.5
during the month, beginning December 48 percent illuminated and with an
angular size of 7.4", and ending it 96 percent illuminated and 4.8" in
Mars is low in the south-west, moving eastwards from Sagittarius into
Capricornus. It has a magnitude of +1.2 and an angular size that decreases
from 4.3 to 4.2" during December, making surface details difficult to see.
Venus, at magnitude -4, is still easily visible in the pre-dawn sky. It starts
the month at an elevation of 17 degrees at dawn, dropping to 10 degrees by
the end. Its angular size drops from 11.6 to 10.9" as its illuminated fraction
increases from 88 to 94 percent.
Astrophysics – December 2012
Jupiter is in a better position to observe this month than for some years. Its
North Equatorial Belt has broadened, and the Great Red Spot, in the South
Equatorial Belt, is currently a pale pink colour.
The Moon occults the open cluster M27 around midnight on the night of
the 3rd to the 4th, with stars disappearing and reappearing.
Saturn, Venus, Mercury and a crescent Moon appear together before dawn
on the 10th and 11th.
The Geminid meteor shower can be best seen after midnight on the 14th
and 15th, with the new Moon not spoiling the view. The meteors come from
dust released by the asteroid 3200 Phaethon, rather than a comet, and the
radiant is near the bright star Castor in Gemini. Remember to keep warm as
you observe!
The lesser-known Ursid meteor shower, with its radiant in Ursa Major near
to the star Kochab in Ursa Minor, can be seen around 2-3am UT on the
22nd and 23rd, producing perhaps 10-15 meteors per hour.
Around new Moon on the 10th-15th, you can see Neptune through
binoculars at magnitude +7.8, close to the star Iota Aquarii.
Jupiter is close to a nearly-full Moon in the east after sunset on the 25th,
and they may even be joined in the sky by something else.
What to look out for on December 25, 2012