To the reader:
The Skywatcher's Diary for December 2001 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
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ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: December 2001
The Moon, just a day past Full, rises about an hour after sunset. Notice that it comes up significantly north of due east -- almost farthest north for the month. Twelve degrees (a fist width) to the upper right of the Moon sits bright Saturn. To the Ringed Planet's lower right hangs Aldebaran, the 1st-magnitude eye of Taurus, the Bull. Capella, brighter than Aldebaran but fainter than Saturn, shines 24 degrees to the upper left of the Moon.
At dawn tomorrow morning the Moon is 1 degree (two moon diameters) to the upper right of Jupiter. Can you still find Venus? The planet's long stint as a morning "star," which began back in March, is coming to an end. With each passing morning, Venus drops a little lower, decreasing the chance you will spot it. Thirty minutes before sunrise the planet is just to the south of ESE and 3 degrees above the horizon. Look from a vantage point with an unobstructed eastern horizon, and use binoculars to help initially locate it.
Saturn reaches opposition today, so we, on Earth, are between the sun and the planet. Saturn rises at sunset and sets at sunrise, which means it will be visible during all dark hours. After opposition, Saturn officially becomes an evening object to astronomers, although the planet has been visible in early evening for some time now. Saturn also shines brightest for the year, at magnitude -0.4. Technically, the planet is the brightest it's been in three decades, but that's a statistical record. The difference in maximum brightness from last year to this is not noticeable.
Mercury is at superior conjunction today, which indicates the planet is on the far side of the sun, as seen from Earth. Because Mercury's orbit is tilted relative to the Earth's orbit, the planet does not usually pass directly behind the sun, from our perspective, but rather a little above or below the day star. Today it slides a degree under the sun. You will have to take our word for it, however, since the sun's brilliance won't allow you to directly verify Mercury's position. Mercury next shows up briefly in the evening sky during January.
Before daybreak tomorrow, the waning gibbous Moon rests high in the SW. If you are out early enough, notice the star Regulus, the heart of Leo, the Lion, 5 degrees (half a fist) to the lower left of Luna. The Moon sits at the base of a rough semicircle of fainter stars that represents the head of the beast. These stars will best be seen once the Moon moves on. The next morning (Friday the 7th) the almost-Last-Quarter Moon appears in the south, 12 degrees to the left of Regulus and 13 degrees to the right and slightly below Denebola, the lion's tail.
Pluto is in conjunction with the sun, so, similar to Mercury two days ago, it is on the far side of Sol. The most distant planet is not directly behind the sun, but passes 10 degrees above it, from our viewpoint. Pluto's orbital tilt is 17 degrees, the greatest of all the planets and more than twice as large as the next contender, Mercury. The highly inclined orbit is one of the bits that has caused some to suggest that Pluto be reclassified and lose its planet status. More compelling is the recent awareness of a group of iceball objects similar to Pluto, although smaller and farther out.
The Moon reaches Last Quarter at 2:52 p.m. This evening marks the earliest sunset for those of us near 40 degrees north latitude. A reasonable, but incorrect, assumption is that the earliest sunset and latest sunrise occur on the shortest day -- the solstice, December 21. The actual situation is more complex. Because the Earth's orbit is slightly elliptical, our planet's speed around the sun varies. This changing rate produces the offset of earliest sunset (today) and latest sunrise (January 5) from the solstice. A similar effect occurs at the June solstice.
At the end of dusk, Orion begins his climb over the eastern horizon. Second-magnitude Bellatrix, the hunter's left shoulder, rises first. The other shoulder, Betelgeuse, pokes up next, followed shortly by the "belt" stars (Mintaka, Alnilam, Alnitak, in that order) and Rigel, the left foot. Three hours after sunset the remaining foot, Saiph, makes its appearance, and completes the well-known winter pattern of seven bright stars.
Tomorrow morning, before dawn, the crescent Moon stands 6 degrees (half a fist) to the upper left of Spica, the brightest star in Virgo. In addition to being the anchor for that zodiacal constellation, Spica is a useful marker for tracing the plane of the solar system. It lies within 2 degrees of the ecliptic, the imaginary line that represents the projection of that plane into space. The ecliptic runs between the Moon and Spica, tomorrow morning, but closer to the star. Regulus, in Leo, and high in the SW at that time, sits even closer to the ecliptic.
Mars continues to hold forth as the brightest object in the southern early evening sky. The planet began this month as a zero-magnitude object, but has now officially dropped to 1st magnitude, registering in at magnitude 0.5. While offering a pleasing sight to the unaided eye, Mars is disappointing in a telescope. Earth has pulled far away from the Red Planet, compared to its closest approach last June. Consequently, Mars has become a small yellow-orange, featureless dot in amateur telescopes. The planet will continue to roam the SW evening sky, growing ever fainter, until June 2002, when it disappears into twilight as a 2nd-magnitude object.
Jupiter rises at the end of evening twilight just to the right (south) of NE. This king of planets then dominates the sky until sunrise. It sits among the stars of Gemini, the Twins. Pollux and Castor, the brightest stars in that constellation, are 12 degrees (a fist width) to the planet's left. Jupiter is currently retrograding, so it is slowly slipping westward relative to the background constellation stars, and away from Pollux and Castor. Note its position relative to the surrounding stars, then look every week or two to detect its orbital motion.
Tomorrow morning a thin "old" Moon, only 32 hours before New phase, hovers 8 degrees (a fist) to the upper right of Venus. The key to successfully spotting Venus is timing. The planet rises only 35 minutes before the sun. Start looking then, and wait for Venus to get high enough to find, probably about 10 minutes later. A flat, unobscured ESE horizon is necessary. Use binoculars to aid in initially spotting the Moon and planet against the bright dawn sky.
The Geminid meteor shower reaches its peak tonight. All of the excitement surrounding last month's spectacular Leonid shower may skew an observer's expectations. The Geminids are a good, reliable shower, much like the Perseids in mid August. An average observer from a dark site should anticipate seeing one meteor every minute, on the average. While that number is a far cry from the one meteor every few seconds that Leonid observers were reporting last month, remember, the Leonid storm was a once-in-a-lifetime event. The absence of moonlight makes this year's Geminids definitely worth a looksee. The best time to observe is anytime after 10 p.m. until the approach of dawn.
A solar eclipse occurs today, so what must be the phase of the Moon? Solar eclipses can occur only when the Moon is near New. This particular eclipse is annular, which indicates that at maximum eclipse the Moon cannot completely cover the "surface" of the sun. It leaves a bright ring of sunlight, the annulus, and consequently the feathery outer corona that is most often associated with solar eclipses will not be visible. For most of the U.S. the eclipse will be partial, and requires special eye protection to view safely. For the eastern U.S., including Michigan, the sun sets before the eclipse ends. The eclipse for us, therefore, occurs at a very low altitude. In Michigan the eclipse begins just after 4 p.m. EST, then reaches maximum near 5 p.m., when 25% or less of the sun is covered. Specific times for various cities and tips for safe viewing can be found at http://sunearth.gsfc.nasa.gov/eclipse/ASE2001/ASE2001.html.
Times of maximum eclipse:
Detroit: 4:57 p.m. EST
Kalamazoo: 5:01 p.m.
Lansing: 5:00 p.m.
The thin crescent Moon, only 26 hours after New, can be spotted, with effort, just after sunset. Look low in the SW (7 degrees to the north of due SW) 25 minutes after sundown. Timing is critical since the Moon sets about 45 minutes after sunset. Use binoculars to help find the hairline crescent sitting just above the horizon. The appearance of the first crescent after New Moon marks the end of Ramadan, the Islamic month of fasting.
The crescent Moon is an attractive sight in the southwestern evening sky over the next several nights. Look an hour after sunset, or earlier if you wish a more colorful, but brighter, background. The Moon is passing through a faint part of the zodiac, the extreme eastern portion of Sagittarius and Capricornus. Consequently, Luna performs solo -- no other bright objects closeby. Mars is the bright star-like object considerably farther to the upper left. The Moon does not reach that planet's vicinity until Thursday.
At the end of evening twilight notice the Summer Triangle. The three brightest stars on the western side of the sky comprise this pattern. In order of brightness they are Vega, Altair, Deneb. Why are they referred to as "summer," you may wonder, when all other traces of that season have vanished? That designation denotes the time of year when the group is visible all night long. Rather than considering the name inaccurate, allow it to remind you of a warm summer evening. It's worth a try.
The sun enters Sagittarius today. As the Earth orbits the sun, our day star appears to travel through the portion of the sky known as the zodiac. The sun advances eastward about a degree per day, so that after a year it scoots completely around the sky. Today the sun appears to cross the boundary of Sagittarius, in which it remains until January 19. This is not the astrologers' Sagittarius that you read about in daily horoscopes. The sun passed into that sign on November 22, and leaves it December 21, according to those who follow the ancient superstition.
At the end of evening twilight the crescent Moon sits 3 1/2 degrees (7 moon diameters) to the left of a 3rd-magnitude star known as Delta in Capricornus. Although bright moonlight may make the star difficult to pick out, success in doing so offers you the chance to find Uranus, also in the vicinity. Delta is the brightest star near the Moon. Binoculars may help you spot it. Notice a 4th-magnitude star, Gamma, 1 1/2 degrees (3 moon diameters) to the lower right of Delta. Uranus sits at a right angle from these two stars, 1 1/2 degrees to the upper right of Gamma. The planet is only 6th magnitude, so you will need binoculars to view it. If moonlight interferes, determine how to find Delta without the Moon nearby, wait a couple of nights until the Moon is well on its way, then try again.
The bright "star" to the upper right of the Moon this evening is Mars. Four and a half degrees (9 moon diameters) separate the two bodies. The 1st-magnitude star 16 degrees (a fist and a half) to the Moon's lower left is Fomalhaut, in the faint constellation of Piscis Austrinus, the Southern Fish. It is the lowest of all the 1st-magnitude stars we see from Michigan, rising only 17 degrees above the southern horizon, at maximum, from the middle of the state. Next lowest of the bright stars is Antares, heart of the summertime constellation Scorpius.
The Winter Solstice occurs at 2:21 p.m. EST, welcoming in the official start of winter in the northern hemisphere. At the exact moment of solstice the sun stands directly over a location on the Tropic of Capricorn in the South Pacific Ocean off the coast of Chile. Today is also the shortest day/longest night of the year for us. The sun is above the horizon for about 9 hours out of 24. While plenty of winter weather still faces us, we can take solace in the knowledge that the amount of daylight begins increasing daily. We have withstood the darkest time of the year.
The Moon passes First Quarter phase today at 3:56 p.m. EST. If the sky is clear you should be able to find the Moon at that exact moment, even though the sun does not set for another hour. Look for Luna a third of the way up in the SE. Once the sky darkens, notice Mars 22 degrees (a fist width) to the right of the Moon, both objects in the south. The planet sets almost 6 hours after sunset, followed by the Moon nearly 2 hours later.
To obtain a star map showing this and other sky events, send a self-addressed, stamped envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824.
With the rising of Sirius in the ESE 3 hours after sunset, the Winter Hexagon is complete. Not a true constellation, the hexagon shape is created by tracing through many of the brightest wintertime stars. Begin with Rigel, the foot of Orion. Proceed to Sirius, 24 degrees (two fists) to the lower left. Then move 26 degrees to the left and slightly up to find Procyon, just above the eastern horizon. Next is Pollux, the brighter of the Gemini Twins, 23 degrees to the upper left. Climb 34 degrees higher to Capella. Then swing back 30 degrees to the right to reach Aldebaran. Finish off the pattern by returning to Rigel, 27 degrees to the lower right.
Today and tomorrow are good days to check the accuracy of a sundial because the Equation of Time is near zero. In other words, apparent solar time (what sundials provide) and mean solar time (clock time) are equal. Normally the Equation of Time correction must be applied to the reading from a sundial in order to agree with your watch. The sundial can be as much as 16 minutes off. Now, however, if the sundial has been properly set for its longitude, no further correction is needed.
While much of the western world celebrates Christmas, the Romans, before Christianity, observed Dies Natalis Invicti Solis, the Birthday of the Invincible Sun. The celebration recognized the sun's emergence from the depths of darkness. Its climb northward had begun once again, and with it, the promise of longer days and warmer weather to come. A number of the customs we observe this time of year have their origins in this ancient Roman holiday.
The Big Dipper, a.k.a. Ursa Major, is circumpolar from mid northern latitudes. It is close enough to the North Celestial Pole that, as viewed in Michigan, the constellation never rises or sets as it swings around the sky. That group of stars, therefore, should be visible to us at all times of night, year round. The Big Dipper is now at its lowest around the end of evening twilight. Although technically visible, it becomes a challenge to find, particularly from an area with houses and trees closeby. Even from a remote location, unless the sky is exceptionally clear, several of the pattern's stars may be lost in haze near the horizon. Test your observing site. How many of the seven stars can you locate?
The Moon occults Saturn early tomorrow morning. After sundown tonight, take note of the Moon's position 4 degrees (8 moon diameters) to the upper right of Saturn. The Moon travels in its orbit roughly its own diameter every hour. By around 4 a.m. (in Michigan) the Moon passes in front of the planet, blocking it from view. Because the Moon is at waxing gibbous phase, 2 days before full, the left edge is still dark. The contrast between the dark lunar limb and the bright planet will make a dramatic event. Although binoculars provide a good view, use a telescope to get the full effect. For exact times of disappearance for various cities, consult http://www.lunar-occultations.com/iota.
Detroit times: Disappearance 3:57:09 a.m. EST, Reappearance 4:37:24 a.m.
Kalamazoo times: Disappearance 3:55:08 a.m. EST, Reappearance 4:38:25 a.m.
Lansing times: Disappearance 3:56:11 a.m. EST, Reappearance 4:37:00 a.m.
If you received a new telescope recently, Saturn and Jupiter -- on either side of the Moon tonight -- make wonderful targets to hone your observing skills. Saturn's rings are magnificent -- sure to delight everyone. The rings are currently tipped significantly toward us, making them easy to examine. Be sure to look for Cassini's Division, a dark "split" in the bright rings. Jupiter's cloud bands should be visible, if the night is clear, and the 4 major moons are easy. They look like stars aligned on either side of the planet. Check hourly to notice their shifting positions as they orbit Jupiter. When you use your telescope, remember to start with the lowest power eyepiece and increase magnification as the conditions and your experience dictate. If you have trouble pointing the scope, practice in daylight by sighting distant towers or buildings.
Overnight the Moon will be eclipsed, so what is the Moon's phase? Lunar eclipses occur when the Full Moon passes through the Earth's shadow. The eclipse is penumbral, so the Moon only enters the light, outer portion of the shadow. Frequently, penumbral eclipses are not detectable without instruments. This time, the Moon plunges deep into the penumbra, so the southern part of the Moon's disk should appear noticeably dusky at deepest eclipse (5:29 a.m. EST). The event begins 2 hours earlier, but don't expect to see much change until near maximum.
The just-past-full Moon rises 20 minutes after sunset. Jupiter is 6 degrees (12 moon diameters) to its upper right. Once the Moon clears the treetops, notice the bright stars Pollux and Castor -- Gemini Twins -- 8 degrees to the left of Luna and 5 degrees apart. Pollux is the lower of the brotherly duo. Tomorrow night the Moon doesn't rise until 1 1/2 hours after sunset. Then it sits 10 degrees (a fist) directly below the Twins.
After you count down the new year tonight, step outside to catch a breath of fresh air and take in the magnificent scene. The brilliant winter stars are at their best around midnight, front and center in the south. This year they are punctuated by bright ornaments: the Moon, Jupiter, and Saturn, draped through Gemini and Taurus. The majestic hunter, Orion, stares down upon us as he has since before humans were around to acknowledge his presence. The steadfastness and beauty of the heavens have inspired humans for thousands of years. They can still work their magic, if we only allow them to do so.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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