This is the fourth in a series of posts about the storied history of Halley’s Comet (officially designated 1P/Halley). If you missed the earlier posts, you can still read Part One here, Part Two here, Part Three here, and Part Four here.
When 1P/Halley made its 1835 appearance, streams of vapor were seen emerging from it. This led German mathematician and astronomer Friedrich Wilhelm Bessel to propose that the jet forces from evaporating comet material could significantly and unpredictably alter a comet’s orbit given Newton’s third law, which states that for every action there is an equal and opposite reaction. Bessel helped refine the orbital calculations for Halley’s Comet.
On November 30, 1835, exactly two weeks after the comet’s perihelion (i.e. its closest approach to the Sun), American writer Mark Twain was born. Years later, Twain famously wrote in his autobiography:
I came in with Halley’s comet in 1835. It is coming again next year, and I expect to go out with it. It will be the greatest disappointment of my life if I don’t go out with Halley’s comet. The Almighty has said, no doubt: ‘Now here are these two unaccountable freaks; they came in together, they must go out together.’
In wonderfully poetic fashion, Twain died on April 12, 1910, which was the very day after 1P/Halley’s perihelion on its return in that year. One might be tempted to think he was waiting for this apparition before giving up the ghost, in which case it’s good he didn’t jump the gun when the Great Daylight Comet of 1910 appeared about four months earlier. As its name implies, that comet was visible in broad daylight even to the naked eye, outshining the planet Venus in what may have been the brightest cometary appearance of the 20th century.
Notwithstanding nearly being upstaged, 1P/Halley was ready for its close-up when it did finally arrive on schedule. By all accounts it was a singularly impressive sight, coming so close during this visit that the Earth actually passed through its tail. It was during the 1910 apparition that the first photographs of the comet were taken. One such photograph (see above) was taken by the Yerkes Observatory, founded in Williams Bay, Wisconsin, only 13 years earlier. Also obtained for the first time in 1910 was the comet’s spectrum–a measurement of the electromagnetic radiation of both the dusty cloud surrounding the comet and its gaseous emissions, which helps derive such properties as chemical composition.
Not to be outdone by such prophecies of the past, this apparition even came with its own doomsday predictions. One of the gases discovered in the tail through spectroscopic analysis was the toxic gas cyanogen, leading French astronomer Nicolas Camille Flammarion to predict that when the earth passed through the comet’s tail, the gas “would impregnate the atmosphere and possibly snuff out all life on the planet.” Perhaps unsurprisingly, Monsieur Flammarion was not only an astronomer but an author of science fiction novels, and fortunately here it seems he let his imagination run away with him. Notwithstanding many panicked Earthlings running out to buy gas masks, anti-comet pills, and apparently even anti-comet umbrellas, the planet suffered no harm given how diffuse the gas was.
This brings us to 1P/Halley’s most recent apparition in 1986, which unfortunately occurred under the worst viewing conditions in the last 2000 years. The comet and the Earth were on opposite sides of the Sun at the time, and the comet never made a particularly close approach. Those living near urban centers had even greater trouble seeing it owing to increased light pollution. We did, however, have one observational advantage over our forebears–the ability to travel into space. Several probes were launched to study Halley’s Comet close up, including the Soviet Union’s two Vega probes, Europe’s Giotto probe, and Japan’s Suisei and Sakigake probes. The probes came to be collectively referred to as the Halley Armada.
1P/Halleys next predicted perihelion will be on July 28, 2061, and conditions for observation are expected to be much better during that apparaition. If my fingers aren’t too arthritic and if the world is not otherwise destroyed in that year as the comet’s appearance itself might herald, I’ll make a point of updating this series of posts with new information then…