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C/1618 W1

Great Comet of 1618

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Through Comet, Telescope and Korea

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It was the first comet to be observed with telescopes (along with two smaller ones in the same year). While leading scientists at the time made precise observations, others discussed at a colloquium whether these comets were divine signs because of the war that had just broken out across Europe, or purely natural phenomena.

Discovery and observation

Three comets were visible in the naked eye in 1618. The brightest of these is probably the one first observed on 25 November. Two Chinese texts reported the sighting of the comet on the morning of 26 November, with its tail measuring 10° long across the sky, pointed to the southeast.

It is possible that the comet was discovered earlier in Persia, where the Spanish ambassador García de Silva y Figueroa had seen it in Isfahan a day or two earlier. However, his reports are inaccurate in this regard. He described it as diffuse and of the color and brightness of Venus in the eastern sky. Sightings were also made in Korea, the Moluccas, and the Philippines.

The comet reached a brightness of 0–1 mag on 29 November. In Europe, the comet was observed by many astronomers from the end of November. Johannes Kepler saw it in Linz on the morning of 29 November and was able to measure its orbit until 7 January. The Swiss Jesuit Johann Baptist Cysat observed the comet from Ingolstadt from 1 December. On December 9, he reported a tail length of 70°. In England, the astronomer John Bainbridge observed it from 28 November to 26 December and drew maps showing the comet's position in the sky. From his observations, he concluded that the comet was ten times further away from the Earth than the Moon.

Longomontanus, a student of Tycho Brahe, reported the comet's tail stretching 104° across the sky on 10 December while the Jesuit Orazio Grassi estimated a tail length of about 60° on 12 December in Rome. Other astronomers, such as Pierre Gassendi, Wilhelm Schickard, and Willebrord Snellius also made observations of the comet.

The comet could be observed in China until 4 January 1619. Its last sighting was by Cysat on the morning of 22 January with a telescope.

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