To the reader:
The Skywatcher's Diary for December 2002 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
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ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: December 2002
Tomorrow morning is the last easy opportunity to catch the slim crescent Moon before it disappears in route to becoming New. An hour before sunrise, look for it 10 degrees (a fist width) above the east-southeastern horizon. Strikingly brilliant Venus perches 13 degrees to the Moon's upper right, and fainter Mars is 2 degrees to Venus' upper right. The star Spica, brighter than Mars, is another 7 degrees to the Red Planet's upper right. Spica, the brightest of Virgo's stars, stands 26 degrees above the southeast. Morning skywatchers should keep an eye on the Venus-Mars duo all month long.
Despite the fact that most of us are shifting into "winter mode," the sky can temporarily transport us back to summer. The Summer Triangle, that stalwart of warmer weather, hangs high in the west as evening twilight darkens. The three 1st-magnitude stars that mark the pattern's tips are widely spaced. Vega, the brightest of the trio, sits more than halfway up in the west. Deneb is half of that distance above Vega. Deneb marks the tail of Cygnus, the Swan. The last of the threesome is Altair, in Aquila, the Eagle. Look for it in the southwest not quite as high as Vega and 34 degrees (approximately 3 fists) to that star's left.
A total solar eclipse occurs today for those lucky enough to be in the right place. The Western Hemisphere is not in the path, however. The narrow band of Moon's shadow that produces the spectacle races across southern Africa, the Indian Ocean, and then drops off the Earth over Australia. This is the last total solar eclipse of any consequence until March of 2006, although several partials and annulars occur in the interim. Incidentally, the circumstances of the 2006 event are similar to another eclipse that some older readers may remember. In May of 1970 it crossed Mexico, Florida, and trekked up the eastern coast of the U.S. Both eclipses belong to Saros cycle 139.
New Moon occurs in the wee hours at 2:34 a.m. EST. Notice that the phase change technically happened the previous day (11:34 p.m. PST) for folks on the West Coast. Jupiter also begins its retrograde today. For the next 4 months the giant planet slowly drifts westward among the more distant stars, crossing the constellation border from Leo back into Cancer. Halfway through the retrograde cycle Jupiter reaches opposition, the period when it appears in the sky all night long.
The Moon returns to the evening sky starting tonight. Look for the young crescent in mid twilight, about 45 minutes after sunset, just to the right of due southwest. It sits only 3 degrees (6 moon diameters) above the horizon. If you look much after that time you're likely to miss the chance, since Luna sets 30 minutes later. Although trees and other obstructions on the horizon easily mask the hairline-thin crescent, give it your best try. There's something magical about the appearance of such a fragile Moon shimmering in the twilight.
Look at Venus and Mars before sunrise some morning soon. The planets slide within 1 1/2 degrees (3 moon diameters) of each other today and tomorrow morning. Venus is the gleaming object found in the southeast during twilight. At magnitude -4.7, it outshines everything but the sun and Moon. Mars, at magnitude +1.7, is 360 times fainter than its sibling, so it could easily be overlooked. One to two hours before sunup is the best time to catch the show. Venus remains in the vicinity of Mars over the next few weeks, slowly climbing higher and veering away from Mars. Near month's end Venus begins settling back toward the horizon while Mars continues drifting westward.
The Moon offers a pleasing face this evening. The almost-4-day-old crescent hangs in the south-southwest. Use binoculars to scan the bright surface looking for interesting features. Using a tripod to steady the binoculars will dramatically improve the view. The crater Langrenus should be visible nearly dead center, recognizable as a bright oval. Craters are also prominent along the terminator (left edge). The Moon sits among the stars of Capricornus, the Sea Goat, but that pattern is too faint to trace with moonlight present. The planet Neptune is also in the region, 8 degrees (almost a fist width) to Luna's upper left, but even less conspicuous than the constellation. Let the Moon pass before attempting to find this distant gas giant. You will need a good finder chart, astronomical binoculars or a modest telescope.
Although the shortest day is still two weeks away, the earliest sunset occurs tonight, for latitude 40° N. This situation seems illogical - you expect earliest sunset, winter solstice and latest sunrise all to coincide. The cause for the seeming inconsistency is the Earth's tilted axis and elliptical (rather than circular) orbit. Unfortunately, the explanation is not simple, so the effect remains mysterious to most people. The quirk has an upside. Most of us are more attuned to sunset than sunrise. Starting tomorrow, therefore, the days will seem to lengthen because the sun sets later. It feels like we're cheating winter, just a little.
The Moon has crossed over into the constellation of Aquarius this evening. Very little is apparent in this part of the sky because all the constellations are faint. This section is referred to as the "watery" portion of the zodiac. It contains the three water-related figures: Capricornus, Aquarius, and Pisces. The brightest object in the vicinity is Fomalhaut, a 1st-magnitude star in Piscis Austrinus, the Southern Fish. Look for it 16 degrees (a fist and a half) to the lower left of the Moon. Uranus sits 6 degrees to Luna's upper right. The most distant planet, Pluto, is in conjunction with the sun today, which means it lies in the same direction in space as our day star, but about 40 times farther away.
Saturn now rises in the east-northeast a half hour after sunset, so it's more than 10 degrees (a fist) up at the end of twilight. The planet climbs high enough by mid evening to become an excellent telescope object. By then Saturn has cleared the thick lower levels of the Earth's atmosphere that distort the magnified image. Those famous rings are particularly showy now because they tilt near maximum to our view. As the planet circles the sun every 30 years, we glimpse the rings in a variety of poses from edge-on to tipped 27° toward our line of sight.
The Moon passes First Quarter phase this morning at 10:49 a.m. EST, so when we see it this evening Luna should appear distinctly more than half full. It remains a good binocular/telescope object for the next few days, providing sharp views of craters along the sunrise terminator (left side). Approximately 30 degrees (3 fists) above and slightly to the right of the Moon sits a large square of nearly equally bright stars. Three of them are technically 2nd-magnitude and one is 3rd. The Great Square of Pegasus, as it is known, is about 1 1/2 fists on a side.
The waxing gibbous Moon rises just after midday, so if the sky is transparent you should be able to spot it later this afternoon in the southeast. After nightfall, see if you can detect the isolated 2nd-magnitude star 16 degrees below the Moon. It goes by the name Diphda, or Deneb Kaitos, the whale's tail. It is the brightest member of the constellation Cetus, the Whale or Sea Monster. Cetus plays the villain in the Perseus-Andromeda Greek myth. The constellation is difficult to trace because it's faint. The pattern is large, however, as a proper whale should be. The Moon doesn't reach the animal's head for three more nights, on December 15th.
The Geminid meteor shower reaches maximum tomorrow before daybreak. The Geminids and summertime Perseids are the two most reliable meteor displays of the year. Under favorable conditions a single observer should spot about one meteor per minute. The peak of activity is broad, so there isn't an exact time to observe. The Moon sets a couple of hours after midnight, so anytime from then until the start of morning twilight is best. Observe from a wide-open location so that you can scan as much of the sky as possible.
For those with access to a telescope, two of Jupiter's moons will cast shadows on the planet tonight. You also may need to be suffering from insomnia, since the event runs during the early morning hours. The first shadow, from the satellite Callisto, appears shortly after 12:08 a.m. EST. Io's shadow joins in at 2:33 a.m. The two cross the disk simultaneously until 4:50 a.m. when Io's shadow drops off, followed by Callisto's 2 minutes later.
Mercury begins a favorable evening appearance. Look for it very low in the southwest to west-southwest 45 minutes after sunset. The planet sits only 2 degrees off the horizon at that time. See if you can spot the 2nd-magnitude star Sigma (in Sagittarius) 2 degrees to its left. A week from now, Mercury will reach 6 degrees (half a fist) up, about the best situation to spot the planet during this apparition. Little wonder most people have never seen Mercury. Timing is the key. The planet becomes more difficult at the end of the month and disappears after the first week of January.
Look for the gibbous Moon in the eastern sky 2 hours after sunset. The Pleiades or Seven Sisters star cluster is 9 degrees (a fist) to the left at that time, but you may need binoculars to pick it out against the Moon's glare. Bright Aldebaran, the star marking the eye of Taurus, the Bull, will be easier to spot, 17 degrees to Luna's lower left. Tomorrow night the Moon jumps to 6 degrees above that star and 8 degrees below the Pleiades.
Saturn reaches opposition tonight, which indicates the planet is opposite the sun, as seen from Earth. It therefore rises at sunset, is visible all night, and is generally at its closest and brightest for the year. Saturn is particularly bright, now, due to two additional factors, unrelated to the opposition. The ringed beauty is near its perihelion, when the planet's closest to the sun during its 30-year orbit. Additionally, Saturn's rings are tilted open to our line of sight almost to their maximum, so they present their brightest face to us. Look for the planet 20 degrees (2 fists) to the Moon's lower left tonight.
As darkness falls the Moon sits 8 degrees to the upper right of Saturn, in the eastern sky. By tomorrow's first light of dawn, the Moon and Saturn have traveled all the way across the sky and will be found in the west only 3 degrees (6 moon diameters) apart. During the middle of the day tomorrow, when the Moon is out of our sight, it edges closest to Saturn, passing 2 degrees from the planet. Tomorrow evening the Full Moon appears 6 degrees to the planet's lower left, back in the east again.
Full Moon occurs this afternoon at 2:10 p.m. EST. Tonight, using binoculars, see if you can detect that the upper right part of the Moon is beginning to recede. The Full Moon of December was known in colonial America as the Long Night Moon or the Moon Before Yule. In earlier times the Roman mid winter festival of Saturnalia began on this date. It was eventually extended 6 additional days. The lively revelry of that ancient celebration has largely been preserved through our modern Christmas and New Years parties.
The Moon rises just less than an hour after sundown. It comes up nearly opposite the direction of sunset. Since the sun is now setting close to its most southerly point, expect the Moon to rise far north. Luna crosses the horizon about 36 degrees to the north (left) of due east, or 9 degrees south of northeast, for mid northern latitudes. The far north rising point means that the Moon will also set north of west. The arched trail it follows during the night mirrors the sun's daily path near the June solstice. Casual observers who see the Moon in the middle of the night at these times often remark at how high the Moon appears.
Winter officially begins (in the Northern Hemisphere) at 8:14 p.m. EST. Several extremes coincide with the December solstice: Shortest day, longest night, the sun's setting and rising points are farthest south, sun's midday altitude is lowest. From this point forward, the astronomical signs improve - days get longer and the sun climbs higher. From a celestial viewpoint this date might better be thought of as mid winter or perhaps the beginning of spring. As everyone is well aware, however, the weather lags the astronomical markers by several months.
The Moon rises in the east-northeast about 3 hours after sunset. Forty-five minutes later, Jupiter pops up 7 degrees (14 moon diameters) below Luna. The two bodies move in tandem across the sky throughout the night while the Moon inches closer to the planet. By dawn tomorrow the pair sits a third of the way up in the west-southwestern sky, and 4 degrees separate them. Tomorrow night Jupiter rises first, then the Moon follows in 30 minutes, 9 degrees to its lower left.
One advantage of the sun setting so early is that the sky becomes completely dark before anyone's bedtime. Youngsters and oldsters both can enjoy the celestial sights without disrupting their sleep schedules. With magnificent Orion and friends now in full display, the view is worth taking in. If you haven't done so recently, pause and inspect the bright stars in Orion. Betelgeuse, the upper left star is a cool giant. Its lower temperature gives the star a reddish-orange hue, particularly when compared to Rigel, the bright one on the lower right. Rigel is significantly hotter than Betelgeuse and, consequently, glows blue-white.
Tonight Jupiter makes an especially intriguing telescopic target. The giant planet and its family of moons always merit a look, but for a period tonight two of Jupiter's moons will simultaneously cast shadows on the planet. The show starts at 8:59 p.m. EST when Europa's shadow begins to cross Jupiter. A moderate amateur telescope will clearly reveal a small dark circle. At 10:55 p.m. it is joined by Io's shadow. The double shadow parade continues until 11:53 p.m. when Europa's shadow leaves the planet's disk, followed by Io's shadow at 1:11 a.m.
If you receive a sundial for Christmas, today is the perfect day to calibrate it. The Equation of Time is now zero. The Equation of Time is not really an equation, but rather an amount of time that indicates the difference between clock time and time read from a sundial. In other words, if your sundial has been properly designed and constructed for your location and correctly mounted, then today it should agree with your watch, assuming the latter is accurately set. The two kinds of time can be out of sync by up to 16 minutes. In most instances the Equation of Time correction is often much less of a problem for sundial users than the errors introduced by poor design or installation.
The Moon attains Last Quarter at 7:31 p.m. EST. Mercury reaches greatest elongation, too. That's astronomy jargon to say that the planet appears farthest from the sun. The angle between sun and Mercury is greatest - 20 degrees at this apparition. It also generally indicates a good time to try to spot this elusive planet. Look in the southwest 45 minutes after sunset. The planet sits about 6 degrees (half a fist) above the horizon at that moment. Although Mercury shines at magnitude -0.5, the twilight glow will make the planet seem much fainter. You may find binoculars helpful. Mercury is fading rapidly, dropping 0.1 magnitude per day, so don't hesitate.
Two hours after sunset the great Andromeda Galaxy sits very near the zenith, for mid northern latitudes. The galaxy, you may recall, is the farthest object you can detect with unaided eye. This colossal group of 300 billion stars lies at a distance of 2 million light years. Use naked eye and binoculars to scan the region. A portable lawn chair that allows you to lie back while gazing overhead is a great accessory. The darker the observing site, the better. From a pitch black location the Andromeda Galaxy is an amazing sight.
Venus is impressive. If you are up before sunrise the planet's hard to miss in the southeast. Venus gleams at magnitude -4.6, 7 times brighter than Jupiter, the next brightest planet. For the next two mornings Luna enhances the view. Tomorrow morning it perches 10 degrees (a fist) to the upper right of Venus. The following morning (Monday) the Moon drops to 4 degrees (8 moon diameters) below the planet. Mars is also in the scene but considerably fainter. Look for it 4 degrees to Venus' right.
Once Venus rises, almost 4 hours before sunrise, until Saturn sets, an hour before sunrise, four planets stretch across the morning sky. Venus and Mars sit in the southeast 4 degrees apart. Jupiter hangs a third of the way up in the west-southwest near the head of Leo, the Lion. Saturn is low in the west-northwest nestled among the winter stars. It's 15 degrees to the upper left of Aldebaran, 15 degrees to the upper right of Betelgeuse. The span from Venus to Saturn reaches nearly 150 degrees.
Tomorrow morning, an hour before sunrise, the old crescent Moon, only two days before New, sits 10 degrees up in the southeast. It's among the stars of Scorpius, which you can verify by spotting Antares, the brightest star in that constellation, 4 degrees to the Moon's lower right. The scorpion, usually thought of as a summer constellation, begins to emerge out of the sunrise glow every year around this time. It slowly climbs the southeastern sky, rising 4 minutes earlier each day.
You might catch a glimpse of the very old Moon tomorrow morning 45 minutes before sunrise. Look almost on the horizon, 7 degrees to the north (left) of due southeast. Use binoculars. If rising early to observe the crescent Moon isn't what you had planned for the first morning of the new year, then how about pausing long enough during the celebrations this evening to step outside, look up and admire the marvelous winter stars and planets. If for no other reason, do it to clear your head for the coming year.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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