Countdown to the Comet : Halley’s, a Snowball 63 Million Miles Away in a Sky Filled With Stars, Makes an Optimum Appearance This Week

With a good set of binoculars, a dark patch of land and a little patience, ordinary earthlings will be able to get their first look at a famous celestial wanderer later this week.

Halley’s Comet, still 63 million miles away, is streaking toward the Earth, and for the first time in 75 years those who are not professional astronomers should be able to see the fabled interloper. The pros have been watching it for a couple of years.

The comet is growing brighter by the day as it draws closer to the sun, and a number of factors should make this week an optimum time for viewing. The comet will pass near an easy-to-find star cluster called the Pleiades, or Seven Sisters, making it possible for amateurs to overcome the most difficult obstacle of all--locating the tiny snowball in a sky full of stars. Of course, all of this depends on good weather. If it is raining, you might want to curl up by the fireplace and wait until December.

If Skies Are Clear

But if the skies are clear, head for a darkened area away from the light pollution of metropolitan regions, aim your binoculars at the right spot, and catch a glimpse of a marvel that has fascinated scientists and laymen for hundreds of years.

If the conditions are right, “anyone should be able to see this cotton ball,” said Stephen J. Edberg, coordinator for amateur observations for the International Halley Watch.

It will even be possible to watch the comet during a civilized time of the evening--about 9 p.m. By December, it will be visible from Southern California only during the early morning hours, just before sunrise.

Edberg, an astronomer with the Jet Propulsion Laboratory in Pasadena, said it will not be necessary to go a long way to find an adequate viewing site, as long as the sky remains dark and any lights are behind the viewer, who will be facing east.

“A half-hour drive up Angeles Crest Highway (in the hills above Pasadena) should do it,” he said.

Allow Your Eyes to Adjust

Professional astronomers usually allow their eyes to adjust to the darkness for about half an hour before beginning observations, and Edberg recommends the same procedure for amateurs. It won’t hurt to look at the sky, but avoid looking at any lights for at least 20 minutes. During that period, he said, stars that had not been visible minutes earlier will slowly come into view as the eyes adjust to the lower light level.

Although most professional astronomers have already seen Halley through large telescopes as it draws closer to the Earth, it is fortunate that the comet should make its layman’s debut at this time. Under even the best of circumstances, it would be hard for amateurs to pick out the comet this early. But this week it will pass through an area of the sky that non-astronomers should be able to find, thus greatly enhancing their chances of seeing the comet.

The Pleiades, which the comet will pass close to, should be easy to find, Edberg said. By about 9 p.m., the star cluster will be due east, about midway between the horizon and directly overhead. The cluster is about the size of a fingertip held at arm’s length, Edberg said, and its tight configuration should stand out from other stars in that part of the sky.

Some observers may also find it helpful to use the belt of Orion, a widely known constellation, as a pointer. By looking upward along an imaginary line drawn through the stars forming the belt, observers should find Halley just before reaching the Pleiades.

Seeing It Through Sunday

By Thursday evening, Halley will be directly below the Pleiades, and it will pass to the right of the cluster as the weekend progresses.

A good set of binoculars of about eight power, preferably with large front lenses to capture more light, offers a field of view that should include both the comet and the star cluster. Sky and Telescope magazine recommends using the Pleiades as the key for capturing Halley.

On Thursday, the magazine suggests, “place the Pleiades on the top edge of the field of view (as seen through the binoculars.) Halley’s Comet should now be near the center of the field or a little below it.

“On Friday, place the Pleiades on the edge at the 11 o’clock position. Halley’s Comet is now near the center.

“On Saturday, put the Pleiades at the left edge to center the comet.

“On Sunday, place the Pleiades on the 8 o’clock edge. This brings the comet to the upper right of center.”

Those positions will vary somewhat, depending on the field of view of each set of binoculars.

How Do You Know?

How do you know when you have seen the comet?

“It will look totally different than anything else in the sky,” Edberg said.

Instead of appearing as a sharp point, like a star, the comet will look like a “cotton ball,” Edberg said.

The hard nucleus of the comet, often described as a dirty snowball, is actually only about two or three miles in diameter, so what viewers will actually see is the cloud of ionized dust and gas that surrounds the head of the comet.

For those willing to take a bold step beyond simply looking at the comet, it should be possible to photograph it, but that’s no simple task. The comet will be so faint, compared even to the faint stars of the Pleiades, that it will be hard to capture on film. The task will be further complicated by the Earth’s rotation making celestial objects appear as streaks rather than pinpoints in the long exposures required for “astrophotography.” Professional astronomers and serious amateurs get around that problem by using a motor-driven tripod that moves the camera so it can track the stars. But that is not a cheap gadget.

Would-be astronomers who do not have that kind of equipment and who are willing to settle for stars as streaks instead of points may still be able to record their observations, Edberg said. A camera mounted on a sturdy tripod, equipped with a shutter release cable and loaded with fast film (ASA 1000 or faster), should produce at least some results, he explained.

Edberg, who is an accomplished astrophotographer himself, recommends using a lens of between 135 and 500 mm.

“Set the aperture wide open and expose for 20 to 30 seconds,” he said.

But don’t offer to sell the photos to Life magazine until you have processed the film.