To the ancient Greeks, these travelers from the outer solar system were known as "hairy stars," from which comes our present word comet.
Records of comet observations exist in the historic writings of many cultures. Although detailed European records of Comet Halley extend back only to 1456, Chinese observations in 240 B.C. may be the first listings of Halley in recorded history.
Using computer models of Comet Halley's motions and the perturbing effects of the planets, scientists have traced back the passages of the comet. Such predicted times of the comet's appearances can then be checked by looking at historical records of many cultures.