Halleys Comet
On this day in 240 B.C., Chinese astronomers first observed the celestial occurrence that later came to be known as Halley's Comet, a recurring phenomenon which has also been offered as the astronomical explanation for the appearance of "The Star of Bethlehem" in Christian tradition. But if in fact, the Three Kings did see Halley's Comet on that day, it was only the first time the comet would be associated with significant historical occurrences. Appearing again in 1066 (and every 75 years or so since the first time it was spotted), Halley's Comet was thought to be an omen by the English predicting defeat in the Battle of Hastings. And more recently, it is said to have book-ended the life of American author Mark Twain, who was born two weeks after its visit in 1835 and died the day after it's next perihelion in 1910.