A.D. 893. A great comet is said to have appeared in this year with a tail 100° in length, which afterwards increased to 200°![216] A.D. 1402. A comet appeared in February of this year, which was visible in daylight for eight days. "On Palm Sunday, March 19, its size was prodigious." Another comet, visible in the daytime, was seen from June to September of the same year. When the orbit of the comet known as 1889 V was computed, it was found that it had passed through Jupiter's system in 1886 (July 18-21). The calculations show that it must have passed within a distance of 112,300 miles of the planet itself--or less than half the moon's distance from the earth--and "its centre may possibly have grazed the surface of Jupiter."[217] Sir John Herschel thought that the great comet of 1861 was by far the brightest comet he had ever seen, those of 1811 and 1858 (Donati's) not excepted.[218] Prof. Kreutz found its period of revolution round the sun to be about 409 years, with the plane of the orbit nearly at right angles to the plane of the ecliptic. * * * * * On November 9, 1795, Sir William Herschel saw the comet of that year pass centrally over a small double star of the 11th and 12th magnitudes, and the fainter of the two components remained distinctly visible during the comet's transit over the star. This comet was an appearance of the comet now known as Encke's.[219] Struve saw a star of the 10th magnitude through nearly the brightest part of Encke's comet on November 7, 1828, but the star's light was not dimmed by the comet. Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude through Biela's comet, although the interposed cometary matter must have been at least 50,000 miles in thickness.[220] Bessel found that on September 29, 1835, a star of the 10th magnitude shone with undimmed lustre through the tail of Halley's comet within 8 seconds of arc of the central point of the head. At Dorpat (Russia) Struve saw the same star "in conjunction only 2"·2 from the brightest point of the comet. The star remained continuously visible, and its light was not perceptibly diminished whilst the nucleus of the comet seemed to be almost extinguished before the radiance of the small star of the 9th or 10th magnitude."[221] Webb says-- "Donati saw a 7 mg. star enlarged so as to show a sensible disc, when the nucleus of comet III., 1860, passed very near it. Stars are said to have started, or become tremulous, during occultations by comets. Birmingham observed the comet of Encke illuminated by a star over which it passed, August 23, 1868; and Klein, in 1861, remarked an exceptional twinkling in 5 mg. stars involved in the tail."[222] The comet of 1729 had the greatest perihelion distance of any known comet;[223] that is, when nearest to the sun, it did not approach the central luminary within four times the earth's distance from the sun!