Halley’s Comet

Halley's Comet (photo by NASA)

May 25, 240 BC: The first documented appearance of the most famous of the periodic comets is made. The comet would one day come to be called Halley’s Comet (rhymes with valley). The Chinese work, Shih chi, tells of a “broom star” seen during the lunar month of May 24 to June 23 in 239 or 240 BC.

Edmond Halley first recognized the periodic nature of this comet. He was working with all observed comets seen between 1337 and 1698. He noted three comets with identical orbits spaced regularly apart in their time of appearance – 1531, 1607, and 1682. He determined that these three comets were, in fact, one comet that showed a periodic reappearance. Working backwards through historic records, it was found that 23 previous visits by the comet had been recorded. According to Halley, the comet would appear again in 1758. He was correct, but did not live to see it, dying in 1742.

Every appearance since the 240 BC event has been recorded somewhere in history. The next visit in 164 BC was recorded in two different Babylonian cuneiform tablets. The orbit as described confirmed that it was Halley’s comet. The next visit – 87 BC – was again recorded by the Babylonians. The most famous appearance was the one recorded in the Bayeux Tapestry in 1066. The closest the comet has ever come to Earth was 0.0342 Astronomical Units or 3.2 million miles.

The last visit from the comet was in 1986, with perihelion occurring in February and March of that year. Perihelion is when as astral body is closest to its center of attraction – in this case, the Sun. The possibility now existed for mankind to visit the famous comet and spaceships were sent out to get a closer look. The Giotto took pictures of the nucleus and showed an irregularly shaped mass, probably mostly ice, with a crater and three trailing jets of molecules. The comet’s orbit is highly elliptical and outside the plane of the major planets. In fact, it is such an ecliptic orbit, it is even outside the non-planet Pluto’s orbit. The next appearance is scheduled for 2062.

“I came in with Halley’s Comet in 1835. It is coming again next year (1910), 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.” – Mark Twain

“Say, Halley’s Comet is coming around again. I didn’t know what all the excitement’s about. I’ve seen it so many times, I’m getting dizzy!” – Bob Hope

“I earnestly wish them all imaginable success; in the first place that they may not, by the unseasonable obscurity of a cloudy sky, be deprived of this most desirable sight; and then, that having ascertained with more exactness the magnitudes of the planetary orbits, it may redound to their eternal fame and glory.” -EdmondHalley

“This sight… is by far the noblest astronomy affords.” -EdmondHalley

Also on this day:
“Swede” Momsen – In 1967, submariner Swede Momsen dies.
Nuking Ourselves – In 1953, the US continued testing with nuclear artillery.