The Importance of Twilight

When Comet West entered the morning sky in March 1976, veteran observer Michael Mattei gave me some valuable advice: "Follow the nucleus into the twilight." So it was that on the morning of March 8th I turned the 9-inch refractor at Harvard College Observatory to the comet and patiently waited for sunrise. While watching the comet's bright, swollen pseudonucleus battle the dawn, I noticed the surrounding coma vanishing in layers. The pseudonucleus began to look peculiar — it was elongated in a line perpendicular to the Sunward direction.

Suddenly, two nuclei snapped into view, one of them itself elongated. I observed again the next morning and found not two but four nuclei forming a trapezoid inside the comet's inner coma. Twilight had filtered out the most intense regions of the inner coma and left behind the stunning signature of a comet being torn apart by the solar forces.

Mattei's advice pertains to all comets, so try making your own observations in twilight. Who knows what surprising structures you'll see! And the drawings we make can be handed down to upcoming generations of comet watchers. Nobody knows when the next great comet will appear. "Like a breaching whale before it plunges into the ocean depths, a comet briefly luxuriates in the sunlight and then is gone," wrote Carl Sagan and Ann Druyan in their book Comet.

So don't wait for the next comet of the century to appear. Explore the hidden depths of the inner nucleus of any comet that happens by. The time to start is now!