How can we study these celestial bodies which are so fascinating but so small and evanescent? In ancient times, scholars merely recorded their passage in the sky, convinced that comets were purely occasional "visitors" to our solar system: since many years often passed between two passages, no one could imagine that it was the same body that periodically reappeared. The first person to realize this was an English astronomer, Edmund Halley, who had been very surprised by a particularly spectacular comet that he could observe in 1682. After having meticulously observed its movements in the sky, he estimated that it moved along a very elongated elliptical orbit. But, if this were true, the comet should have already been observed in the past at regular intervals: it would have been enough to examine the descriptions of comets during the last few centuries to discover which ones matched the comet in 1682. Soon Halley discovered that two "passages", those in 1531 and 1607, had the same characteristics as "his" comet and he deduced that the period that it takes to complete the elliptical orbit must be about 76 years: the next appearance of the comet would thus have occurred in 1758. Too late for the English astronomer to observe it in person a second time: he died at the age of eighty-six, 16 years before the comet reappeared. And now, what had become a famous comet, was given his name: Halley. But the studies of this celestial body did not stop with his death. On the contrary, other astronomers patiently continued to look back in time for even older passages through all the historical records available around the world: and they discovered 21 passages (prior to 1531), the oldest of which dates back to 87 B.C.. And what is even more important, the comet was expected every 76 years and it was always right on time: in 1835, in 1910 and finally, in 1986, the year in which the scientific community finally could utilize the most efficient observation systems - the automatic probes already tested so successfully to explore the planets in our solar system.
How can we study these celestial bodies which are so fascinating but so small and evanescent? In ancient times, scholars merely recorded their passage in the sky, convinced that comets were purely occasional "visitors" to our solar system: since many years often passed between two passages, no one could imagine that it was the same body that periodically reappeared. The first person to realize this was an English astronomer, Edmund Halley, who had been very surprised by a particularly spectacular comet that he could observe in 1682. After having meticulously observed its movements in the sky, he estimated that it moved along a very elongated elliptical orbit. But, if this were true, the comet should have already been observed in the past at regular intervals: it would have been enough to examine the descriptions of comets during the last few centuries to discover which ones matched the comet in 1682. Soon Halley discovered that two "passages", those in 1531 and 1607, had the same characteristics as "his" comet and he deduced that the period that it takes to complete the elliptical orbit must be about 76 years: the next appearance of the comet would thus have occurred in 1758. Too late for the English astronomer to observe it in person a second time: he died at the age of eighty-six, 16 years before the comet reappeared. And now, what had become a famous comet, was given his name: Halley. But the studies of this celestial body did not stop with his death. On the contrary, other astronomers patiently continued to look back in time for even older passages through all the historical records available around the world: and they discovered 21 passages (prior to 1531), the oldest of which dates back to 87 B.C.. And what is even more important, the comet was expected every 76 years and it was always right on time: in 1835, in 1910 and finally, in 1986, the year in which the scientific community finally could utilize the most efficient observation systems - the automatic probes already tested so successfully to explore the planets in our solar system.
