Bright Stars, great December Meteors and Two Comets.
by Leo Enright
The
December night sky always features a wonderful display of brightest
stars. Locally, sunset time varies by only eight minutes over the whole
month. On December 1, sunset here is at 4:25PM EST, and is only a few
seconds earlier from evening to evening until by December 10 it is at
4:24PM. That is the date of the earliest sunset of the whole year.
After that, the sunset time is again just seconds later from day to day
until by December 31, it is at 4:33PM. In the mornings, the change is
slightly greater from day to day, but still less than one minute per
day, as the sunrise time moves from 7:25AM on December 1 to 7:47 on
December 31. Locally the latest sunrise of the year is not until
January 3. Perhaps most of your friends may simply think that both
earliest sunset and latest sunrise occur on the date of the Winter
Solstice, which this year is December 22. The solstice simply means
“the sun stands still”, and by carefully watching the sky, you can see
that fact actually happening. All you need to do is observe the sun’s
evening setting position on the western horizon over a period of
several weeks, and note that it goes slightly southward each day until
the solstice, when it stops and starts moving northward
evening-to-evening. Similarly watching the sunrise position over
several weeks will show it moving southward along the eastern horizon
until the solstice, when it “stands still” and then starts moving
northward again. In short, “solstice” is about POSITION of the sun, NOT
about TIME of sunrise or sunset.
December nights bring to
prominence the brilliant display of bright stars around the head and
shoulders of Orion, the Great Hunter, as he marches across our southern
sky, followed by his familiar hunting dogs, Canis Major and Canis
Minor. The stars, Betelgeuse and Bellatrix, indicate his shoulders;
Rigel and Saif mark his knees, and Alnilam, Alnitak, and Mintaka show
his belt. Straight to the left from his belt is the brightest star in
the whole sky, Sirius, the eye-star of his larger dog, and above it and
a bit to the left is the sky’s sixth brightest star, Procyon, the eye
of the smaller canine. Above and to the left of Betelgeuse are Castor
and Pollux, the twin-gentlemen of Gemini. To the right of Orion’s other
shoulder (Bellatrix) is reddish Aldebaran, the bloodshot eye of Taurus,
the great Bull, whom the Hunter is pursuing westward across the
heavens. Turning around to the northwestern sky, we can see the three
bright stars that dominated the sky in the summer and early fall, but
they are now setting – the Summer Triangle. One of them, that we knew
then as Deneb, brightest star in Cygnus the Swan, is still easily seen,
but it seems to be at the top of a large cross standing upright on the
northwestern horizon. Little wonder mediaeval Christians called it, not
Cygnus, but “the Northern Cross” which dominates that part of the sky
during the month before Christmas. Be sure to enjoy its view as well as
that of the bright stars in the south.
Among the five bright
planets that may be seen with the unaided eye, only three of them are
readily visible during the entire month of December. Jupiter, which for
months has been a bright object low in the southwestern sky after
sunset, may perhaps be seen there, but only for the first few days of
December. Mars is the planet that dominates the evening sky this
December. This bright reddish object, seen among the stars of the
constellation Gemini, rises in the east at the end of evening twilight
on December 1, and slightly earlier each evening until by the end of
the month it may be seen shortly after sunset. Over the month its
brightness increases dramatically; early in the month Mars is outshone
by Sirius (see above), but by mid-month, it will be noticeably brighter
than even that star. Its brightness will continue to increase until
near the end of December. For those who have a telescope, Mars will
appear larger, and show more surface detail, than at any time over the
next eight years. Careful observers will notice it moves to the right
among the stars and in the direction of the constellation Taurus.
Saturn, seen among the stars of the constellation Leo the Lion, rises
in the east about midnight in early December and slightly earlier each
evening until at month’s end it may be seen at 10PM. The final
naked-eye planet to be seen is brilliant Venus, which completely
dominates the morning sky in the three hours before sunrise. It is
still bright enough to be seen in the daytime. In fact, in the past
month, while observing in the early morning hours, I have been easily
able to see my shadow from the light of Venus alone. Try that some
morning when there is no moon, or other object like an outdoor light,
to create a distraction. Mercury may not be seen this month because its
direction is too close to that of the sun.
Try to watch the moon
this month as it moves past several of the planets. On the morning of
December 1, it appears close to Saturn. In the eastern sky on the
mornings of December 4, 5, and 6, watch the waning crescent moon to the
right of Venus. Try to see it on each one of those mornings in order to
appreciate how far the moon moves in the sky in a 24-hour period. Be
sure to watch the Full Moon as it appears to be close to Mars on the
night of December 23.
Though
I rarely suggest that readers ought to observe an object that requires
binoculars, I will now make an exception. This month there will be two
fairly bright comets in the sky, ones that will require binoculars to
appreciate. First, Comet Holmes (officially called Comet 17P/Holmes, at
left) is a truly remarkable object which I have been observing night
after night since October 24. On that day, an extremely remarkable
event occurred. For some reason (still not completely understood by
astronomers) something happened to a rarely seen comet originally
discovered in 1892. Within hours this comet suddenly exploded in
brightness from an object far too faint to see even with a large
amateur telescope to naked-eye brightness! The greatest comet outburst
ever recorded! Also, its coma (the halo of gas and dust around the
comet’s nucleus) expanded from a small sphere to the largest object in
the solar system – in a matter of about three weeks! It has been slowly
moving through the constellation Perseus, which is easily seen well up
in the northeastern sky in the evening, and about mid-way between the
large “W” of Cassiopeia which is above it and the very bright star
Capella, which is below it. Among the brightest stars of Perseus, use
your binoculars to find this large glowing coma and then follow it from
night to night as long as you can. The second comet is called Comet
Tuttle (officially Comet 8P/Tuttle), and it may reach, or almost reach,
naked-eye brightness in late December. On the nights of December 19 to
25, it will be crossing right through the middle of the “W” of
Cassiopeia (see above). This comet may have a distinct tail much more
easily seen than that of Comet Holmes.
On the nights of December
13 and 14, the annual Geminid Meteor Shower reaches its peak. This
shower is often regarded as the best, or second best, of the whole
year. If the sky is cloud-free, it is indeed worth watching. Face in a
southeast or southwesterly direction, dress warmly, relax on a
reclining lawn chaise well away from any light pollution, and enjoy the
show. Record the numbers of meteors (sometimes incorrectly called
“shooting stars”) that you see per hour.
More information
about observing the night sky is available in the book “The Beginner’s
Observing Guide” now on sale at Sharbot Lake Pharmacy.
