By Dean Regas
Enquirer contributor

Sky watchers in Cincinnati have not seen a naked eye comet since 1997. But the drought may be over. Not one, but two comets will visit our evening skies this month. ... and one of them is really NEAT.

A warning: comets are notoriously fickle objects. Most brighten as they approach the Sun. In 1996, Comet Hyakutake lit up the evening sky with its wispy light blue tail, followed by comet Hale-Bopp's bright fly-by in the spring of 1997.

Others just fizzle out. The greatest astronomical disappointment was Comet Kohoutek. Visible in 1973, the media heralded Kohoutek as the "Comet of the Century." But it remained dim and was barely visible to the naked eye. Kohoutek was dubbed "Comet Watergate" by disillusioned observers.

A comet's life

A comet is basically a dirty snowball of ice and dust. The nucleus (the only solid part of the comet) ranges from 1 to 20 kilometers in diameter. Astronomically speaking, that is very small. However the coma, or envelope of gas surrounding the nucleus, can be 10,000 to 100,000 kilometers in diameter. And the tail of comets can be as long as 1,000,000 to 500,000,000 kilometers long. That means some comets can become even larger than the Sun!

Unlike the relatively circular orbits of the planets, comets cut highly elliptical paths around the solar system. Comets spend most of their lives in the dark, cold regions of the outer solar system. But every once in a while comets enjoy a fleeting fling with the Sun. As a comet approaches the Sun, the ice heats up and turns into vapor. This vapor forms the coma and leaves a stream of material in its wake - a delicate and beautiful tail.

The length of time to complete one orbit around the Sun varies greatly from comet to comet. Short period comets orbit the Sun once every 1-200 years. Halley's Comet swings by the Earth every 76 years - that's considered short. But long period comets like Hale-Bopp and Hyakutake will not be seen again for 4,200 and 30,000 years respectively.

Naming comets

Comets are named after their discoverers. Comet hunters are a rare and dedicated breed, but most are amateurs. Japanese amateur astronomer Yuji Hyakutake discovered the comet bearing his name using a pair of large binoculars. And this April, Australian astronomer William Bradfield discovered his 18th comet in 32 years of searching. Comet Bradfield was visible to binocular observers late last month.

Several comets in the 1990s were discovered by two astronomers at the same time. Comet Hale-Bopp was co-discovered by Alan Hale and Tom Bopp. Likewise Comet Shoemaker-Levy 9, which crashed into Jupiter in 1994, was the ninth comet discovered by the team of Gene and Carolyn Shoemaker and David Levy.

These days, it is more difficult for amateur astronomers to discover comets. Facilities with larger telescopes such as The Lincoln Near Earth Asteroid Research (LINEAR) project and the Near Earth Asteroid Tracking (NEAT) program are finding them first. These projects were designed to monitor asteroids visiting our neighborhood. During their searches, NEAT has found 41 comets, and LINEAR has tagged 128.

The two comets heading our way this month bear the inauspicious names NEAT 2001 Q4 and LINEAR 2002 T7, but we will simply refer to them as NEAT and LINEAR.

NEAT-o

NEAT should be the better of the two. Visible to the naked eye about May 7-20 in the western sky just after sunset, it should be as bright as second magnitude stars like the North Star. Unfortunately, the glow of the setting sun will wash it out significantly. LINEAR will be more difficult to view for observers in the northern hemisphere.

LINEAR will be crossing the sky so far to the south that it will not be visible from Cincinnati until it begins receding to the outer solar system.

Binocular alert!

LINEAR will join NEAT in the evening sky from late May to mid June. However, by then you will need binoculars to see both of them - but what a rewarding scavenger hunt! Visit www.aerith.net/comet/weekly/current.html for updates on NEAT, LINEAR, and other comets.

With comets there are no guarantees. But hopefully Comets NEAT and LIENAR will brighten up your May evenings this year.

Observatory events

Coming up at the Cincinnati Observatory

Sun-day Sunday

May 9, 1-4 p.m.

Celebrate Mother's Day and the sun at the Observatory. The Sun is the star attraction on this Sunday and you can learn all about our nearest stellar neighbor. Sun-day Sunday includes hourly classes about the Sun, tours of our historic buildings, and safe viewing of sunspots and solar flares out of our 1843 telescope (weather permitting). As a special treat we will also have free sundaes for those in attendance.

Cost: $5 for adults, $3 for children

Advance reservations are required - space is limited. For further information or to make reservations, please call 321-5186.

Comet Days

May 14 and 15, 9:00 p.m.-midnight

NEAT is coming and nothing can stop it. NEAT will be the first naked-eye comet to grace the evening sky since Hale-Bopp in 1997. The Cincinnati Observatory will celebrate this event with a two-day open house - Comet Days.

Comet Days include classes, tours, and viewing of Comet NEAT, Jupiter, and Saturn through of our historic telescopes (weather permitting).

Cost: $2 per person

No advance reservations required. For further information or directions, visit www.cincinnatiobservatory.org or call 321-5186.

Dean Regas is the Outreach Astronomer at the Cincinnati Observatory Center. He can be reached at deanobservatory@zoomtown.com.