30 November 1835
Explanation:
Twain was born two weeks after Halley's Comet's closest approach in 1835; he said in 1909: 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.
