Comet Hale-Bopp (C/11995 O1) continues to be visible in the April sky. It's the best comet we've had to view since ­ well, since last spring. We have had an extraordinary run of luck in the last two years to have such spectacular comets to watch. We had better make the most of it, because it's unlikely we shall have an opportunity to view such a spectacular comet for another 20 years, the rough, average interval between really good comets.

        As this is being written, March 20, 1997, the whole comet, head and tail, is brighter than ­0.3 magnitude. Some observers place it at ­0.8. The tail is easily visible to the naked eye, even with moderate light pollution. If you view it from a dark location outside of town, a short drive for us in Morgantown, you can see a naked-eye tail up to 30 degrees long.

        Begin looking for this comet in the northwest about 45 minutes after sunset tonight when it's about 26 degrees above the horizon. Hale-Bopp is bright enough to be one of the first objects that becomes visible as darkness falls. Before the end of astronomical twilight, about 1 ½ hours after sunset, you'll be able to make out the tail as well as the head, or coma, of the comet. When twilight ends, all sunlight will have faded from the sky and Hale-Bopp will be about 19 degrees above the horizon.

        The coma is produced by the sublimation of the ices of which the nucleus is composed and hides the nucleus, its provider. This veil of gas and dust that we see as the "head" of the comet now extends to a diameter of about a million miles. The nucleus is estimated from Hubble observations to be about 25 miles across. This is larger than the nucleus of Comet Halley, measured during a fly-by of the European Space Agency's Giotto in 1986 to be about 5 miles by 9 miles. The tail visible to the naked eye is more than 100 million miles long. Pressure from the solar wind and sunlight always makes the tail point away from Sun, even as it moves away from Sun after reaching its closest approach, perihelion, tomorrow night.

        Hale-Bopp is near its brightest right now, although it could surprise us, as some comets do, and brighten even more after passing closest to Sun. It will be highest in our sky, that is visible for the longest interval after sunset, on April 7 and 8. On those evenings the comet will be more than 21 degrees above the northwest horizon at the end of twilight, about 9:25 p.m., and will set about 12:15 a.m. These first two weeks in April should be ideal, if it is clear, for viewing the comet. Even our Moon, at new phase on April 7, is cooperating. For a few days after April 7 the waxing crescent moon will make a pretty picture in the western sky along with Hale-Bopp. Mercury is also visible in the western sky during the first week of April, but it sets by about 9:30. At first it will be nearly as bright as the comet, but it fades quickly at the end of the week. Moonlight will hinder our ability to see the comet's tail from the middle to the end of April, and in May Hale-Bopp will begin to sink into the glow of sunset. By May 13 it will set just as twilight ends.

        Because the comet will never be higher than 21 degrees in the dark sky, it will be too low to view well with the 14-inch telescope of the WVU Physics Department's Tomchin Observatory. Your binoculars will give a better view, anyway, of the comet's tail and coma than the limited field of view that results from the greater magnification of the telescope. I urge you to find a dark location outside of Morgantown and enjoy this, the most awesome and, perhaps, the rarest of celestial phenomena visible to the naked eye.