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May Night Sky


In 1995, Comet 73P/Schwassmann-Wachmann 3 did something unexpected: it fell apart. For no apparent reason, the comet's nucleus split into at least three mini-comets flying single file through space. Astronomers watched with interest, but the view was blurry even through large telescopes; 73P was a hundred and fifty million miles away.

Now, we are going to get a good look at those comet fragments. In May 2006, what is left of Comet 73P is going to fly past Earth closer than any comet has come in more than twenty years.
There's no danger of a collision. The closest fragment will be about six million miles away, or about twenty-five times farther than the Moon.

The number of fragments has been changing since astronomers first noticed the comet. When the breakup began, in 1995, there were only three pieces. Astronomers are currently tracking nineteen fragments as of mid-April.

Though it is very uncertain, and forecasters consider it unlikely, the expanding cloud of dust from the 1995 break-up of the comet could brush past Earth in May 2006, producing a meteor shower. Astronomers believe the dust cloud is expanding too slowly to reach Earth only eleven years after the break-up; but that all depends on what caused the comet to fly apart.

The most likely explanation for the fragmentation is thermal stress, the icy nucleus probably cracking like an ice cube dropped into hot water as it approached the Sun after a long journey through the cold outer solar system. In this case, the debris cloud should be expanding slowly, and there will be no strong meteor shower. On the other hand, the comet could have been shattered by a collision with a small interplanetary boulder. That type of breakup would produce faster moving debris that could reach Earth in 2006.

It wouldn't be the first time a dying comet produced a meteor shower. Comet Biela, which was seen to split in 1846, and had completely broken apart by 1872, produced at least three very intense meteor showers, producing three thousand to fifteen thousand meteors per hour in 1872, 1885, and 1892.

Assuming a thermal breakup for 73P, scientists have calculated the most likely trajectory of its dust cloud. Their results indicate the dust should reach Earth in 2022, producing a minor meteor shower but nothing very spectacular. The shower watch begins on May 12.

Ironically, even as close as the fragments will come to Earth, they will not be very bright. The largest fragments are expected to be as bright as third- or fourth-magnitude stars, only dimly visible to the unaided eye. These are mini-comets, unlike the Great Comets Hayutake and Hale-Bopp, of 1996 and 1997. Those could be seen with the naked eye even from light-polluted cities. The fragments of 73P will be best viewed away from the pollution of city lights. And don't forget your binoculars for the best view.

From May 1 through 3, 73P will be passing across the lower half of the famous Keystone of Hercules. Then it will pass south of the brilliant blue-white star Vega in the constellation of Lyra on the morning of May 8. In the nights that follow, the comet will turn southeast and will race across the Milky Way, in Cygnus, from May 10 through 12. On May 15, it moves into western Pegasus, and will graze Pisces May 21 and 22.

If you plan to look for the comet, you should also be aware of the waxing Moon during early May. Its increasing brightness will make dim, fuzzy objects like the comet harder to find. The best time to look for P73 will be after the moon has set and before the morning twilight.

Generally speaking, from May through 9, the comet will appear highest in the sky, almost overhead, between 3:00 and 4:00 a.m. The Moon will have set earlier in the night, leaving the sky nice and dark for comet hunting.

• Venus will rise after 3 a.m. and then fade into the morning light. The moon and Venus make a good morning couple on May 23.
• Look for Mars low in the east after sunset. Check out the Moon and Mars on May 1 and 2.
• Jupiter will be low and bright in the evening eastern sky, and should be overhead about midnight. Jupiter and the Moon make a great pair on May 11.
• You will find Saturn above Mars in the west after sunset. The moon is beside Saturn on May 4.
• The full moon will be on May 13 and the new moon will be on May 27.

If you have a question, comment, or suggestion for Charlie, e-mail him at:

Astronomy down under

The Albuquerque Astronomical Society will present a free lecture entitled "Making the Connection Down Under," by TAAS president Judy Stanley, at UNM's Regener Hall on Saturday, May 13, at 7:00 p.m.

Stanley will speak about her adventures during her recent trip to Australia and her observations of the Southern Hemisphere's night sky. While attending the South Pacific Star Party, an annual event hosted by the Astronomical Society of New South Wales at a remote site three hours west of Sydney, Stanley observed astronomical showstoppers such as the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way, and its inhabitant, the Tarantula Nebula; Eta Carinae, one of the most massive and luminous stars known; and 47 Tucanae, an immense globular cluster nearly 120 light years in diameter.
Stanley and other TAAS members who have visited Australia will provide travel, accommodation, and contact information for those who are interested in experiencing astronomy down under.
Stanley is a longtime amateur astronomer, a Project Astro educator, and the director of education for the LodeStar Astronomy Center.
Regener Hall is located on UNM's Main Campus, west of Popejoy Hall. For information and a map, visit or call 254-TAAS.


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