The history of astronomy is the history of the science that studies celestial bodies, from simple observation to theories about the universe. Astronomy includes the study of planets and their satellites, comets, meteors, stars, black holes, galaxies and solar systems.
To underline the importance the importance of the contribution of this science Romfilatelia issued a special souvenir sheet that is devoted to the Return of Halley's Comet, in 1986.
Halley's Comet is the most famous of the periodic comets, and could be seen about every 75-76 years. The comet received the English astronomer's name, Edmond Halley. By applying Newton's gravitational theory and taking into account the gravitational effects of Jupiter and Saturn, he managed to establish the approximate date of the next reversion of the comet.
The firsts sighting of Halley's Comet could not be calculated, but the first mentions of it were made by the Chinese in 611 BC. It was observed in 467 BC and 240 BC.
Halley belongs to the category of short period comets. Comets of this type have an average inclination relative to the ellipse of only ten degrees and an orbital period of just 6.5 years, making Halley's Comet's orbit an atypical one. This suggests that the Halley Comet was originally a long period comet, whose orbit was perturbed by the gravitational pull of the giant planets, the periodical closeness to the Sun, and sent into the inner solar system.
One of the most famous passes, recorded on the no less famous Bayeux Tapestry, was in 1066, when it stunned William the Conqueror's army; since then, no less than 950 years have passed.
An interesting story about the Halley Comet is linked to the fate of American writer Mark Twain, who was born in 1835, two weeks after the comet's passing. In 1909, Mark Twain wrote in his autobiography that he came along with the comet and would go with it. And he left in April 1910.
No less famous was its last crossing, in 1986, becoming the first comet over-flown by a space mission, namely Giotto and Vega.