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Dudley Observatory
Supporting research and education in astronomy, astrophysics, and the history of astronomy |
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Skywatch December 2004
Thursday December 2, 2004 Observe the Last Quarter Moon on November 5th. The New Moon occurs on November 12th. Saturn is the only unaided-eye planet in the evening now. It rises around 8 P.M. at the beginning of December and as early as twilight by the end of the month. In another hour Saturn will appear above the buildings and trees. Saturn forms a crooked line with Pollux and Castor in Gemini. Saturn shines several times brighter than either of these two stars. Venus and vastly dimmer Mars rise together before the first light of dawn as December begins. Locate the Great Square, of the constellation Pegasus, almost straight overhead. From the northeast corner, find three bright stars in a long line, arcing across the sky west to east, just south of Cassiopeia, the big W. From the middle of these three stars (called Mirach) go north towards Cassiopeia past one star, Mu Andromedae, to a second star, Nu Andromerae, in a slightly curving line. The Anromedia Galaxy named M31 is just barely visible to the unaided eye on a good dark night, just to the west of Nu Andromedae. In the finderscope , Aim at Nu Andromedae and the galaxy should be easily visible in the finderscope. In the telescope the galaxy M31 looks like a bright oval embedded in the center of a long patch of light, which extends clear across th e field of view. Off to the south, and a bit east, is what looks like an oversized star making a right triangle with two faint stars. This Is the companion galaxy, M32. Increasing the magnification, you can see it is an egg-shaped cloud of light. With M31 in the center of your low power field, M110 is just outside the field of view, to the northwest. Its on the opposite side of M31 from the other little companion, M32. Its dimmer, and spread over a larger area, than M32, making it harder to see. It has an oval shape, elongated north to south. The Andromeda Galaxy M31 is the largest of 20 or so galaxies, including our own Milky Way galaxy, which make up the “Local Group”. With 300 billion stars, and a diameter of 15,000 light years, it is considerably larger that the Milky Way. It is a spiral galaxy, but since we are seeing it nearly “on edge”, its harder to see any spiral structure, especially in a smaller telescope. The best estimates locate this galaxy at 2.5 million light years from Earth. It is the most distant object the human eye can see without a telescope. In the 1920’s Hubble calculated the enormous distance to this galaxy, using observations of special stars called “Cepheid” variable stars in M31. This is the Skywatch Line for Monday, December 6,
The sky at sunset is remarkably bland. There are no bright planets. Things change rapidly after twilight’s end. By 10 PM Orion, the Hunter, and Sirius, his dog, are well up in the East. Below Orion is Lepus, the Rabbit. Just to the right of Lepus should be a faint, fuzzy object. Binoculars reveal it to be Comet Machholz. Like all comets, this is named after its discoverer. Donald Machholz, of California, is a veteran comet hunter; this is his tenth find. He used a small amateur telescope and spent nearly 1500 hours before finding it. The comet will be best seen next month. It is now visible to rural skies. Suburban light pollution may hamper backyard observation. Ordinary binoculars should be sufficient, while telescopes enhance the experience.
Saturn is well placed for observation at this time. The Ringed Planet appears below Gemini, just to Orion’s left. Saturn materializes as a much brighter star below the twins. Saturn is a great telescope object. Saturn is also of news interest. The Cassini space probe is circling Saturn and gathering data. Attached to Cassini is Huygens, a probe that will soon detach from the mother ship and penetrate Titan’s atmosphere. Not much is known about the Solar System’s largest moon, and one with an atmosphere. Will Huygens land or splash down?
The Moon and Jupiter rise at about the same time, 1:50 AM. They appear in the dim constellation Virgo. They are separated by about one degree and make a very nice duo in binoculars or telescope. The Moon is a thin crescent. At 3:40 AM, the Moon begins to occult, or hide, Jupiter. First, several of Jupiter’s moons fall victim to our satellite, then the planet itself is covered. Since Jupiter is fairly large, it takes about a minute for the Moon’s lit rim to cover the entire planet. After about an hour, Jupiter and its satellites emerge from the dark side.
Clear Skies
Joe Slomka
Skywatch Line for Wednesday, December 8, 2004 Sue French 374-8460
At one time or another, almost everyone has looked up at a starry sky to see a shooting star flash across the sky. Although the blaze of light may look like a falling star, it has nothing to do with the stars and is more properly called a meteor. Meteors are caused by bits of debris from space dashing through our atmosphere. The material is vaporized and leaves a shining trail of heated meteoric particles and atmospheric gases.
This is a good time of the year to spot meteors. Tonight is the peak of the Monocerotid meteor shower. Although it only produces a few meteors per hour, there are several other meteor showers overlapping it. The Chi Orionids, which reached their peak a week ago, last until about December 15th. The Sigma Hydrids are still working toward their peak on December 11th. More impressively, the Geminid meteor shower has just begun.
The Geminids, with their high rates and reliability from year to year, are the shower of choice for veteran meteor observers. This is usually the strongest shower of the year and may produce nearly 120 meteors per hour near peak. This year’s peak is predicted for the evening of December 13th. After that, the activity drops off sharply so that few Geminids are visible after December 17.
Most meteor showers occur when Earth passes near the orbit of a comet. Debris that the comet has left behind is swept up by the Earth and vaporized as it streaks through our atmosphere. The parent body of the Geminids was long undiscovered, but in 1983 the IRAS (EYE-rass) satellite found the asteroid 3200 Phaethon (FAY-ah-thon). It travels in the same orbit as the Geminid meteoroids and is suspected to be the denuded core of an old comet. Geminid meteor particles are far denser than those from other showers.
This is one of the few showers known to put on a good show before midnight, although you are likely to see more meteors after that time. The Geminids produce numerous bright meteors, but lingering trains are rare. Near maximum, there are many bright fireballs with vivid colors. Early evening meteors favor the eastern half of the sky, while those visible in the middle of the night may be seen almost anywhere.
Meteor watching at this time of the year is a chilling experience. A lawn chair, a sleeping bag, a heavy hat, and plenty of warm clothes can help ensure a pleasant skygazing session.
Thursday December 9, 2004 The New Moon occurs on December 11th. Observe the First Quarter Moon on December 18th. Find Cassiopeia, a W shape of five stars overhead, towards the northeast. Within this constellation are more than two dozen open star clusters. Numbering the stars of the W 1 to 5, from left to right step from star 1 to star 2 and continue one third of the distance farther. That is where the star cluster NGC 457 is located. NGC 457 is also called the Owl Cluster. This interesting cluster really does look like an upside down little owl in the night sky. On a dark night without a bright Moon, this cluster really looks like tiny diamonds sprinkled on a black velvet sky.
NGC 457 is located about 9,000 light years away from us. It consists of about 30 light years in diameter. The two bright stars that make up the eyes of the owl may not be part of the cluster, but just stars that to our line of sight appear to be a part of this star cluster. If these stars are part of the cluster, they must be very bright. Some people see NGC 457 as a dragonfly or ET the extraterrestrial. Dress warm and relax in a lawn chair. Observe the Milky Way galaxy stretching across the Fall sky, from horizon to horizon. Look at Cassiopeia and you will see many star clusters appearing as small clouds. With a good star chart at your side, you can figure out what star clusters you are observing.
This is the Skywatch Line for Monday, December 13.
The Sun sets at 4:22 PM, with night falling at 6:04. Dawn breaks at 5:37 AM, with the Sun rising at 7:18.
As the Sun sets, a very thin, two day old, Moon hovers over the southwestern sky. If you can’t find it without aid, binoculars may help. The Moon sets by six PM.
Tonight’s sky is quite busy. By 10 PM, Orion is well up and obvious to even the beginner. Below Orion is a dim constellation, Lepus, the Hare. Scanning with binoculars just to the right of Lepus reveals a hazy patch. This is Comet Machholz. Over the coming weeks, the comet steadily climbs until it cruises past the North Pole. Comet Machholz has been sighted in Colonie skies, and is certainly better in rural areas.
Dawn’s light finds the rest of the bright planets. Jupiter now outshines Saturn. Jupiter is moderately high in the southeast, in the dim constellation Virgo. Jupiter forms an open pair with the bright star Spica. Mars and brilliant Venus pair up, low in the south-east. They occupy diamond-shaped Libra. If they are too low to see at dawn, wait until just before sunrise, when they are much higher.
Saturn glows below Gemini, to Orion’s left. The planet slowly glides westward for a few weeks. Saturn is the highlight of any observing session, and is usually the first thing a new telescope is aimed at.
Gemini is the focus of another event: the annual Geminid meteor shower. Midnight is the ideal time to watch for Geminids. Usually meteor showers are the result of a comet’s litter field. When Earth crosses this debris field, a meteor shower results. Also most annual meteor showers have been known from antiquity. The Geminids are relatively new; they were discovered about 150 years ago. In the 1980’s, astronomers revealed the origin to be the asteroid 3200 Phaethon. But is Phaethon an asteroid or a comet? It displays elements of each. In any case, simply dress warmly and gaze toward the twin stars, Castor and Pollux, and enjoy the show.
Clear Skies
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