ASP: Monster Comet Promises Big Show

Observing Comets

James C. White II
Middle Tennessee State University

This past spring, as Comet Hyakutake decorated our evening skies, I received a telephone call from an upset parent. "We bought our daughter a telescope to see the comet," she said, "and we can't see anything!" The exasperated mother said they found binocular and naked-eye views to be better than those through the telescope. "What are we doing wrong?" she asked.

Absolutely nothing! For novice telescope users, comets through the eyepiece disappear. They are pretty faint objects. They may be bright overall, but all that light is coming from a big area of space. Even out in the suburbs, the contrast between the diffuse cometary glow and the not-so-dark night sky can be lost. A telescope, by gathering light from only a small patch of the sky, often just makes it worse.

Naked-eye comet-watching is the easiest and most satisfying way to begin, particularly in a rural area. Find yourself the darkest location possible, set up the chaise lounge, break out the hot chocolate, and look up. Binoculars are a nice addition; they allow you to gather a bit more light, while still providing a wide field of view. I recommend binoculars with at least a 7-degree field of view. In suburban and urban areas, the binoculars are crucial. You need that extra light-gathering ability.

OK, you say, I found Comet Hale-Bopp this evening. What next? Comets are not big fireballs that sprint across the heavens; theirs are leisurely strolls. Because they constantly change as they ramble about our skies, comets provide us with an opportunity to observe astrophysical phenomena on short time scales. As you observe Hale-Bopp or any other comet, consider the following:

Does the comet have a tail? If so, has its appearance -- color, length, width -- changed since your last observation?

Can you see two tails (dust and plasma)? If so, are there color or shape differences between the tails?

Has the shape or color of the coma changed?

How does the brightness of the comet compare to nearby deep-sky objects? This is a way to see whether the brightness has changed.

If you have access to a telescope, try to use it as well, but keep the power low. The telescope will enable you to study subtle structural changes in the comet's tail(s) and coma, but it's not necessary.

JAMES C. WHITE II is a professor in the Department of Physics and Astronomy at Middle Tennessee State University in Murfreesboro. This article is adapted from his "Guest Observer" column in the November/December 1996 issue of Mercury magazine. In each issue of Mercury, White's column describes an observing project and explains how you can prepare and send us a report of your observations. We select one of these reports for publication in an upcoming issue of the magazine.

Comet Hale-Bopp will pass through the inner solar system during March and April 1997. As it makes its closest approach to Earth, the comet will pass far to the north, above the plane of the solar system -- almost directly above the Sun.

During the spring, the comet will pass through the northern constellations: between the Great Square of Pegasus and Cassiopeia (which is shaped like a 'W' or a '3'). Hale-Bopp passes nearest the Earth on March 23 and nearest the Sun at perihelion on April 1. As the comet passes the Sun, its gaseous tail will be blown backward by the solar wind.

Those in the temperate latitudes of the Northern Hemisphere will have the best view of Hale-Bopp. In late March and early April, the comet will appear in the early morning before dawn, about the width of a hand above the northeast horizon. In the early evening after dusk, look a handspan above the northwest horizon. As the comet moves between Cassiopeia and Pegasus, it will pass very near M31, the spiral galaxy in Andromeda. You'll need a good pair of binoculars to see M31, but Hale-Bopp should be easy to spot with the naked eye.

JAY RYAN is the author of "Starman", an astronomical comic strip featured in the newsletters of over 120 astronomy clubs. "Starman" is also available at http://www.cyberdrive.net/~starman.