Harley published the theory of comet astronomy in 1705, and announced that the great comet that caused great panic in 1682 would reappear in the sky in 1758 (later, he estimated that Jupiter might affect its motion and postponed its return date to 1759). At that time, Harley was over 50 years old and knew that he would never see this great comet again in his lifetime. So he wrote in the book: "If the comet finally reappears around 1758 according to our prediction, only future generations will not forget that this song was first discovered by an Englishman ..."

Some people laugh at Harley's nonsense, some people are skeptical about Harley's prediction, but many people believe Harley's prediction. The French mathematician Crajo made an accurate prediction before the return of the comet: due to the influence of Jupiter and Saturn, the comet will pass the perihelion one month before and after April of 1759.

Comets, commonly known as "broom stars", are celestial bodies orbiting the sun. People have discovered more than 1600 comets, but few can be seen with naked eyes, and only more than 20 can be seen with telescopes every year. Comet is the largest but smaller celestial body in the solar system, of which Halley's comet is the largest and the easiest to observe. The period of this comet is 76 years, which was first calculated by a British astronomer named Halley, so it is called Halley's comet.