The Great Comet of 1556 (usually designated C/1556 D1) was a comet that could be seen with the naked eye in February 1556, and was observed throughout much of Europe.
Discovery and observation[]
The comet was first seen in the evening sky in late February 1556. However, a general observation did not take place until the middle of the first week in March. Its apparent diameter was equal to half that of the Moon, and the tail was said to resemble "the flame of a torch agitated by the wind". Cornelis Gemma, the son of Gemma Frisius, said that the head of the comet, when it first appeared, was as large as Jupiter and that its color resembled that of Mars, though the reddish color gradually faded. He observed a tail length of 4°.
An astronomical broadsheet by Paul Fabricius, showing the map of the 1556 comet's course
Paul Fabricius, a mathematican and doctor at the court of Emperor Charles V in Vienna, described and drew the apparent path of the comet in the sky from March 4 to March 15th (pictured right), though the original map alongside the detailed description is lost.
This comet was also observed in China, and on March 1st had a tail 1° long, growing to 3° before the comet disappeared around May 10.
Orbit[]
Due to the limited number of observations, only a parabolic orbit with limited precision can be determined, which is inclined by around 32° to the ecliptic. At the point of orbit closest to the Sun (Perihelion), which the comet passed on April 22, it was located around 73.4 million km from the Sun, between the orbits of Mercury and Venus. The comet is unlikely to return to the inner Solar System.
Alleged connection to the Great Comet of 1264[]
Grounding his calculations upon elements deduced from Conrad Wolfhardt's chart along with some other crude data gathered from old records, and comparing the result he obtained with the account given by Friar Giles of Cambridge of a grand comet which appeared in 1264, John Russell Hind was led to conclude, as Richard Dunthorne had been in the previous century, that the Great Comet of 1556 was the same comet from 1264. At any rate, he found a high degree of probability in favor of the conclusion at which he had arrived, and argued that the bodies of these years were identical. Hence, he concluded that a return to perihelion might be looked for about the middle of the 19th century, 1848 to 1850. This prediction failed, and as of 2021, no observed comet has matched the orbital elements of either comet.
David A. Sargent writes that available evidence points to there being no connection between the comets of 1264 and 1556.