Night doubleheader: eclipse plus comet Heavens: Tonight offers a skywatcher's delight. A lunar eclipse will darken 92 percent of the moon's face. Meanwhile, Comet Hale-Bopp is visible after sunset.

March 23, 1997|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Comet Hale-Bopp is now one of the best and brightest comets of this century. And if you haven't yet looked up to see it, Mother Nature is throwing in a lunar eclipse tonight. No extra charge.

Tonight's partial lunar eclipse begins at 9: 58 p.m. EST as the moon's orbit around the Earth carries it into the darkest portion of the long shadow our planet casts into space.

If skies are clear, look for the full moon's bright disk to begin darkening at its lower left edge. Lunar eclipses, unlike eclipses of the sun, are safe to watch directly. Binoculars are even better.

The deep coppery color will gradually spread across the moon until only a bright arc of moonscape -- like a snowcap -- is left in direct sunlight at the moon's "top" rim.

At that moment, about 11: 40 p.m., the moon's face will be 92 percent in shadow, and the eclipse will be at its maximum.

The reddish color results when sunlight is filtered and scattered by the atmosphere at the edges of the Earth, then reflected from the moon. The same filtering produces the Earth's reddish sunsets and sunrises.

The darkened moon should let the planet Mars shine more brightly. Mars is near its closest approach to Earth this year. Look for a reddish "star" just above and to the right of the moon.

After 11: 40 p.m., the moon will begin to emerge from the Earth's shadow into direct sunlight. By 1: 21 a.m. tomorrow, the moon will be in full sunlight again.

(Even though the Earth's rotation eastward makes the moon appear to move across the sky from east to west, the moon's slow monthly orbit around the Earth actually moves it through the Earth's shadow from west to east.)

Marylanders' next chance to see a total lunar eclipse without leaving home will be on Jan. 20, 2000. If you miss Hale-Bopp, however, there's no telling when you'll see another comet.

It is shining as brightly as Halley's Comet in 1910. And after many weeks as the brightest object in the northeastern sky before dawn, it has moved to a more civilized evening spot, low in the northwest after sunset.

Yesterday, the comet was 122 million miles from Earth. That's 30 percent farther away than the sun, but the closest it will come. It is visible for about 90 minutes after sunset. Look below and to the left of the W-shaped constellation Cassiopeia. But if you can see those stars, you won't need them. Hale-Bopp is five times brighter.

Dr. John D. Trasco, associate director of the Astronomy Department at the University of Maryland, has watched the comet before dawn from his bedroom window in Laurel and from the College Park campus.

"It's really quite a spectacular sight," he said. "This one is the first [comet] I've seen from around here since Comet West [in 1976] that really looks like a comet. It actually has a tail, and it's a very impressive thing."

Comets are not so rare; six are visible in northern skies. But most are without tails and too dim to be seen without telescopes.

"This is the brightest [comet] in 200 or 300 years," Trasco said. "It's as bright as [the bright star] Vega which you rarely get with respect to comets."

The Maryland Science Center hopes Inner Harbor visitors will see it tonight after 7 p.m., tucked between the Harbor Court and Hyatt Hotel towers.

Bright lights might make it seem "more starlike," said Jim O'Leary, director of the Davis Planetarium. "We'll hope for clear skies and see what happens."

Hale-Bopp was discovered in July 1995. Its large nucleus of ice, dust and frozen gases is thought to be 25 miles wide.

Solar energy is turning the ice to gas and boiling the gas and

dust into the huge, visible cloud, or "coma," around the nucleus.

Part of the coma is blown away by the "solar wind" -- atomic particles streaming out from the sun. It's like chimney smoke in a stiff breeze, and it gives a comet its familiar tail. Comet tails always point away from the sun.

Observers with telescopes are reporting that Hale-Bopp has two tails -- a bright one of dust and a faint one of ionized gas. They also see unusual features near the nucleus that they describe as "hoods," rays, arcs and fountains.

Hale-Bopp has been on a 4,200-year solar orbit that carries it 33.5 billion miles away from the sun, nine times as far from the sun as the most distant planet, Pluto.

Nearly all of that orbit is below, or south of, the plane on which the planets circle the sun. The comet is visiting northern skies briefly while making its turn around the sun. It will soar within 85 million miles of the sun on April 1, then head south again.

Its departure for deep space will be visible from the Southern Hemisphere.

The following organizations are planning public viewings of the eclipse or the comet:

Harford County Astronomical Society. 7 p.m. nightly, today through Thursday and April 1-8 at the observatory, Harford Community College. Call 410-836-4155.

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