Principal Skinner tells Bart that he missed the chance to name a discovery after himself once, but that he got back at Principal Kohoutek. This may be in reference to an actual comet discovered by a Czech astronomer named Kohoutek in 1973. It is known officially as Comet Kohoutek.
The title refers to Halley's Comet that returns to every 75 to 76 years. Not only is it the best known of the comets, historians have traced it returns back to 240 BC. Halley's periodic returns have been subject to scientific investigation since the 16th century. The three returns from 1531 to 1682 were used by Edmond Halley enabling him to predict its 1759 return.
The trivia items below may give away important plot points.
This story was partially inspired by a true incident. On 24 June 1938, a 500-ton meteor entered Earth's atmosphere at a sharp angle and started to burn up, and then impacted just outside of Pittsburgh, Pennsylvania. Scientists believe that had it come straight down (rather than at an angle) it would have destroyed the entire city.
Homer reassures his family by telling them that when the comet hits the earth, it will be no bigger than a chihuahua's head. Later, when the comet does indeed break up, Bart picks up a piece of it, and a chihuahua is standing next to him.