Sid Hammerback states that Mark Twain (Samuel Clemens) was born "......the day Halley's comet first appeared". While it's true that Twain's birth and death both coincide with appearances of the comet (in 1835 and 1910), but Halley's observation was based on the sighting of 1682 (the only one that occurred in Halley's lifetime). He predicted its reappearance in 1759, which he did not live to see. Earlier records of the comet's appearance go back to 240 BCE in Chinese records, so the 1835 appearance Sid refers to is definitely not the day "it first appeared".
A further error occurs because each time the comet appears, it's visible for about 2 - 3 months, so there's no exact "day". Twain's birth occurred about six weeks after its appearance in 1835; his death about four weeks after its appearance in 1910.