To the reader:
The Skywatcher's Diary for December 2003 has been prepared by
David Batch. Credit to the author and to
Abrams Planetarium,
Department of Physics and Astronomy at
Michigan State University, and mention of
our
Sky Calendar, would be
appreciated.
A sample issue of the Sky Calendar is available over the Internet. It
can be viewed via the World-Wide Web at
http://www.pa.msu.edu/abrams/SkyCalendar/Index.html
If you would like a printed sample of the December issue, please send a long,
self-addressed stamped envelope to:
December Sky Calendar
Abrams Planetarium
Michigan State University
East Lansing, MI 48824
Each month, the Department of Physics and Astronomy at Michigan State
University makes the Skywatcher's Diary available over the Internet. It can
be accessed at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Diary.html
Current and back-issues of the Skywatcher's Diary are available in our
archives
at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Archives.html
ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: December 2003
The bright "star" 5 degrees (10 moon diameters) to the upper right of the Moon
tonight is Mars. The planet continues to be a pleasing naked-eye object, although
it's no longer much to look at in amateur telescopes. The separation between
Earth and Mars has grown too great; the planet's tiny disk, as viewed through the
eyepiece, does not reveal any of the surface features that were evident last
summer.
Mercury will be easier to spot over the next couple of weeks thanks to its proximity
to Venus. The two planets can be found low in the southwest within 45 minutes of
sunset. Brighter Venus is more easily picked out of the twilight glow, about 7
degrees (less than a fist) above the horizon. Mercury sits 7 degrees to Venus'
lower right. Last night you might have noticed that a 3rd-magnitude star, Lambda
in Sagittarius, was less than a degree to the lower left of Venus. Tonight the star
is more than a degree below the planet. Use binoculars.
The Summer Triangle's presence in the evening sky continues even though its
seasonal namesake is a distant memory. The three bright stars that form the
pattern can be spotted in the west, about halfway between horizon and overhead.
A favorite faint constellation, Delphinus, the Dolphin, accompanies the Triangle.
Look for a small parallelogram positioned to the east (left) of the line connecting
the stars Deneb and Altair. It's 15 degrees (fist and a half) to the upper left of
Altair, and twice that distance to the lower left of Deneb.
The parallelogram that marks Delphinus measures only about a degree on a
side. Two of its stars are 4th magnitude and two are 5th magnitude, so it can't
stand up to the glare of streetlights. In a dark sky, however, the pattern is obvious.
The two brighter stars have strange names: Sualocin and Rotanev. They honor a
19th century Italian astronomer Nicolaus Venator. Do you see the connection?
Spell the star names backwards.
Saturn currently rises about 2 hours after sunset, so it climbs high enough for
convenient telescopic viewing by mid evening. Look for it in the east-southeast.
It's the bright "star" between the Gemini Twins (Pollux and Castor) and Orion. By
the end of the month, the planet rises as the sun sets. The magnificent ringed
world doesn't require enormous magnification. A modest telescope with good
optics will easily reveal the rings.
Forty-five minutes after sunset look for the 2nd-magnitude star Nunki, 2 degrees to
the lower left of Venus. The planet, at that time, sits 9 degrees (a fist) above the
southwestern horizon. Mercury can also be spotted 7 degrees to Venus' lower
right. The Moon, two days before full, lights up the opposite side of the sky. The
Pleiades star cluster can be found 7 degrees to Luna's left, although binoculars
may be needed to distinguish it within the Moon's glare.
Tonight the Moon cavorts between the Pleiades and Hyades star clusters. The
Pleiades cluster is easily recognized as a group, whereas the Hyades is more
diffuse. The collection of stars around Aldebaran, eye of Taurus, comprises the
Hyades cluster. Aldebaran is the bright star 7 degrees (14 moon diameters)
below and slightly right of Luna. Aldebaran is not part of the cluster, but rather a
foreground object about half as far away as the Hyades.
Full Moon occurs at 3:37 p.m. EST. Tonight's sunset is the earliest of the year for
mid northern latitudes. Contrary to intuition, the earliest sunset, latest sunrise,
and shortest day do not coincide. The shortest day occurs on the winter solstice,
as expected. But earliest sunset and latest sunrise are offset on either side of the
solstice by about two weeks. Most people don't notice the displacement since the
sunrise and sunset times change so slowly this time of year, and the length of
day remains essentially constant over the entire 4-week period.
Mercury reaches its farthest extent east of the sun today. Generally speaking, this
"greatest elongation" provides the best time to view Mercury in the evening sky.
How good the sight of this elusive planet becomes, however, is modified by the
time of year and latitude. For northern latitudes, a greatest eastern elongation that
occurs in spring produces the best view of Mercury. Tonight look for the planet low
in the southwest, 8 degrees (a fist) to the lower right of brighter Venus.
The Moon visits Saturn this evening. The pair of objects rises slightly to the south
(left) of northeast about 1 1/2 hours after sunset. The celestial partners separate
as the night progresses. They stand 4 degrees (8 moon diameters) apart at first.
By midnight the span reaches 6 degrees, and as they disappear into tomorrow
morning's twilight the separation is 8 degrees.
Jupiter reached western quadrature yesterday, which is astronomers' way of
saying the planet lies 90 degrees west of the sun. It also means the planet is
near its minimum phase, as seen from Earth, although that's merely a bit of trivia
since Jupiter is still 99 percent full. Mars reaches eastern quadrature later this
month and the situation is quite different. Because the planet is significantly
closer than Jupiter, its phase will be only 87 percent full. Mars should look
distinctly "out of round" in a moderate telescope.
A planetary challenge for tonight: Can you spot Venus and Saturn at the same
time? Venus sets and Saturn rises within 40 minutes of each other. During that
brief time, if the sky is clear and you have unobstructed views toward the east-
northeast and southwest, both planets should be visible. The ideal time to
attempt a sighting is an hour and forty minutes after sunset. At that moment each
planet will stand 2 1/2 degrees above the horizon. If you are not successful at first,
continue to try each clear night. The length of time that both planets are visible
increases by 6 or 7 minutes per night.
The Geminid meteor shower reaches its peak tonight. No one notified the Moon,
apparently, since the bright gibbous phase will spoil the show. The Geminids is
one of the two most reliable showers of the year. Summertime's famous
Perseids is the other. We can usually count on a meteor every minute, on the
average, out of these two showers, that is, when the weather and the Moon
cooperate. If you'd like to make the best of a less than ideal situation, observe
anytime from late evening until before dawn.
Tonight Mercury slides by Nunki, the same star that Venus passed on December
6, and at nearly the same distance. Look for the 2nd-magnitude star 2 degrees to
the lower left of Mercury. Use binoculars. Mercury sits low in the southwest about
45 minutes after sunset. Be careful not to mistake it for brighter Venus, which is 7
degrees higher, and farther south (left).
Before sunrise tomorrow morning, the Moon rests 4 degrees (8 moon diameters)
to the upper left of Jupiter. Both objects are within the boundary of the
constellation Leo, the Lion, although below the brighter stars that are associated
with the outline of the famous beast. The lion's heart, marked by the bright star
Regulus, lies about 20 degrees (2 fists) to the right and above the Moon and
planet.
The Moon reaches Last Quarter at 42 minutes past noon EST today. Last quarter
moons precede the sun across the sky by about a quarter day, so you should
expect the Moon to rise in the middle of the night and set near midday. If you are
unlikely to be in a conscious state before sunrise, you will have ample opportunity
to greet our faithful celestial companion during morning daylight hours. Look
toward the west to southwest.
As the Moon runs through its cycle of phases, most people understand that we
always see the same side of the Moon. Well, almost the same side. The Moon
does a slight wobble during the course of the month known to astronomers as
"libration." (Not libation -- that's what causes humans to wobble.) Consequently,
if we're patient, over time we can observe nearly 60 percent of the Moon's surface.
The reasons for this lunar listing are the Moon's tilted rotation axis, the Moon's
oval rather than circular orbit, and the parallax that occurs by observing from either
side of the Earth. For more information, see the website
http://www.minervatech.u-net.com/moon/not_libr_ac.htm
The Moon sits on either side of the star Spica early today and tomorrow. Luna
appears 7 degrees (14 moon diameters) above Spica this morning before
sunrise. Tomorrow morning it's 10 degrees (a fist) to the lower left of the star.
Spica is the brightest star in the constellation Virgo and is often pictured as
representing the shaft of wheat that the maiden holds in her hand.
Today was the original date of Saturnalia, the ancient Roman festival that
predates Christmas. Eventually the celebration was lengthened to 7 days.
Saturnalia was a time of wild revelry when the social order was turned upside
down. Rich and poor were equal. Masters ate with slaves and exchanged gifts.
The roots of the event were the midwinter (solstice) celebrations of Egypt,
Babylonia, and Persia. It's believed that the early Christians chose this time to
celebrate Christmas so that they would not draw attention to themselves.
An old crescent Moon hangs gracefully above the southeast horizon shortly before
sunrise tomorrow. Early risers may also glimpse Antares, the heart of Scorpius, 7
degrees below and slightly left of Luna. The best time to catch both objects is 45
minutes before sunrise. At that time the Moon is poised 10 degrees (a fist width)
above the horizon. Observers in Florida have the best chance to see an even
older and thinner crescent the following morning, if they look 15 minutes earlier.
For latitudes north of about 40 degrees, the Big Dipper is circumpolar, that is, it's
always above the horizon. This time of year at the end of evening twilight the
Dipper sits lowest in the sky, just skimming the northern horizon. If you've got a
dark sky and an unobstructed view to the north, determine how many of the
Dipper's seven stars you are able to find. The end of the handle will be the most
challenging.
The Solstice occurs at 2:04 a.m. EST, announcing the beginning of winter for the
Northern Hemisphere. Because the event happens simultaneously around the
world, its passing is marked according to the time zone of the observer. Our
English cousins, for example, observe it at 7:04 a.m. For friends and family on the
West Coast the solstice occurs 56 minutes before the calendar turns to Monday.
The Moon is New at 4:43 a.m. EST. The Moon also reached perigee (Moon
closest to Earth) less than 24 hours ago. Although this perigee was not as close
as last month's, the Earth and Moon are still relatively near -- 222,661 miles.
Those influenced by ocean tides should expect higher levels than usual. Coastal
inhabitants should be particularly alert if the tides combine with storm surges.
The first crescent after New Moon is visible tonight 30 to 45 minutes after sunset.
Look low in the southwest. Brilliant Venus aids the search for this captivating
sight. Forty-five minutes after sunset the planet hangs 14 degrees (1 1/2 fists)
above due southwest. The Moon rests 4 degrees off the horizon, 11 degrees
below and slightly right of Venus.
Take a few moments out of your busy schedule to observe the Moon and Venus
this evening. The crescent and planet pose 5 degrees (10 moon diameters) apart
in the southwestern sky. Forty-five minutes after sunset might be about the right
time to look if you also want to catch maximum sunset color. But you should be
able to spot the pair anytime from 30 minutes to 2 hours after sunset.
The crescent Moon continues to be a pretty addition to the evening sky over the
next several evenings. It also provides an ideal first target for anyone who
received a new telescope over the holidays. The Moon is the easiest celestial
target, and the crescent's side-lit craters -- those along the terminator -- offer the
budding astronomer instant reward. If you have difficulty finding and focusing on
the Moon, try practicing in daylight on neighborhood objects: lampposts, street
signs, radio towers.
Once some time has been spent carefully examining the Moon, Saturn makes a
good second target for the new telescope observer. Its rings are discernable in
modest telescopes and even some high-powered binoculars. The planet rises in
the east-northeast shortly after sunset, but don't be in a hurry. Wait two or three
hours for it to climb above the thick atmosphere so that the image is less
distorted.
Mercury has left the evening sky. In fact, it passed inferior conjunction, between
Earth and Sun, two days ago. The planet slipped 2 degrees above the sun,
unnoticed. It was 63 million miles from us at the time. Mercury next makes a good
morning appearance, beginning shortly after the New Year. It returns to the
evening sky in March.
The Moon joins Mars the next two nights. This evening it sits 7 degrees to the
lower right of the planet. Tomorrow night look for it 7 degrees to Mars' left. In
between, the Moon turns First Quarter. Officially that happens at 5:03 a.m. EST.
Both objects reside in a particularly faint part of the sky, among the stars of
Pisces, the Fishes, although during daylight hours tomorrow the Moon cuts
across the corner of Cetus, the Whale.
Two separate combinations of three planets can now be observed stretching
across the evening skies. The first is Venus (southwest), Mars (south), and
Saturn (east-northeast). Look for them from an hour after sunset until Venus sets,
about 1 1/2 hours later. The second planetary threesome occurs once Jupiter
rises, around 6 hours after sunset. Then it's Jupiter (east), Saturn (southeast),
and Mars (west). These groupings are a prelude to early spring when all five
naked-eye planets will be visible at once.
Saturn reaches opposition today. That is, the Earth is between Saturn and the
sun, so the planet appears opposite the sun in earthbound skies. Saturn also
appears closest to us during oppositions. Because Saturn's orbit is elliptical,
though, the Earth-Saturn distance varies. On subsequent oppositions, occurring
at roughly yearly intervals, Saturn will gradually appear farther away. Saturn is now
closer to Earth than it will be until December 2032.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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