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15 july 2019

I've seen two comets in my life, that I remember. The first was Halley, the comet I'd been looking forward to since my childhood. Growing up in the 1960s to lore about Halley's Comet, I added up the years till 1986 and figured that if rare cancers, random carwrecks, or the ever-popular Bomb didn't get me, I would easily live to see the Comet return. When it did, it was a big Meh. You couldn't see it with the naked eye, where I was living in New Jersey. Rutgers University opened a telescope to comet-watchers and I took a look. Halley's Comet, even through the instrument, looked like a little smudge. So much for hype.

My second comet was Hale-Bopp in 1997. This was the real deal, a distinct streak across the sky even in light-polluted North Texas, and even better through a telescope. Hale-Bopp, unpredicted, promised gratuitous viewing pleasure: until a bunch of eschatologically-minded folks in California decided they'd catch a ride to Heaven on the comet. Their subsequent suicides cast a pall on the memory of what should have been pure bliss.

Comets offer an odd mix of wonder and worry. They are effectively harmless … well, tell that to the dinosaurs, I suppose; comet collisions may have caused extinction events in the past, including the one at the end of the Cretaceous. But from the perspective of human lifetimes, indeed the whole history of humanity, comet impacts are simply not a thing. That doesn't stop us from constructing disaster movies around the possibility.

The greatest comets command visual attention to the point where it's hard to believe they don't portend anything. Andrew Karam, in his Reaktion book Comets, quotes Isaac Asimov on comets as harbingers of disaster: "The sad fact is that disasters come every year and comets have nothing to do with it" (91). Ancients including Aristotle saw comets as meteorological phenomena, happening within Earth's atmosphere – thus making it plausible that their exhalations could affect us. The ancients were wrong, but though we later learned more about comets, the extra knowledge didn't stop us worrying about their noisome effects. When cyanogen gas was observed in the tail of Halley's Comet, many assumed that humanity were goners. Somehow, we survived.

Karam offers a solid account of comet science, and an entertaining look at cultural appropriations of comets from antiquity through science fiction. For all their pyrotechnics, comets are pretty basic objects. "Dirty snowballs," Fred Whipple called them, and scaled to astronomical dimensions, that is exactly what comet nuclei are. Their unglamorous cores are teased out into splendor by the gases evaporating as they near the Sun. One problem for astronomers is how comets can return over the centuries while so profusely fizzling away on every trip. Karam explains that the amount of ice lost on each swing, while highly visible, is pretty small in terms of mass. (So it was with the cyanogen in 1910; there just wasn't enough of the stuff to poison anybody.) A "baked Alaska" effect (60) keeps the center of the snowball frozen as the outside boils off. Eventually even the most massive comet will erode away over the æons. But so will everything. Let's just enjoy stuff on the way to maximum entropy.

Karam classifies comets in art as incidental, dramatic, or cartoonish (81-82). The most famous picture of a comet is of Halley's, flaring up in 1066 on the Bayeux Tapestry: it is perhaps incidental, dramatic, and cartoonish all at the same time.

Shakespeare frequently mentions comets, usually in the history plays (Karam cites Julius Caesar: "When Beggers dye, there are no Comets seen, / The Heauens themselues blaze forth the death of Princes," Act 2, Scene 2). But both Marina in Pericles and Kate in The Taming of the Shrew are gazed on like comets; Shakespeare associated comets not just with literal skyborne portents but with showy human beings. Marina and Kate are like comets, and so too is Henry IV in Part 1, counseling his wayward son Hal to show himself less often so that he will seem more remarkable.

Comets are mentioned in Tasso and in Milton. In later poetry they seem rarer, though the blankness of my memory is not to be trusted too far. Emily Dickinson referred once to "the Comet's chimney," but just as a figure of speech for something really high. T.W. Higginson remembered her saying "'And people must have puddings,' this very timidly and suggestively, as if they were meteors or comets." I am not quite sure what Higginson was getting at, except to express (via Emily Dickinson) the nature of comets, at once commonplace and amazing.

Karam does not get into the debate over how to pronounce "Halley." Growing up with "Rock Around the Clock," I pronounced the astronomer's name like Bill Haley's, to rhyme with "daily"; but when 1986 rolled around, newsreaders soberly rhymed the comet with "Alley." Where's the fun in that?

I do not remember comets in song – well, except for the obvious one, "Comet / Will make your face turn green," which has nothing to do with literal comets. For all their showiness, comets are truly ephemeral and have not penetrated the verbal imagination of the West very deeply.

Karam, P. Andrew. Comets. London: Reaktion, 2017.