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Updated: May 22, 2025
Eight satellites Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, and Japetus accompany the planet; Mimas, the nearest to its primary, rotating on its axis in 221/2 hours, and revolving at a distance of only 120,800 miles, whilst Japetus, the most remote, occupies 79 days in its rotation, and revolves at a distance of 2,314,000 miles.
Between Titan and Japetus the sixth and seventh reckoning outwards there was obviously room for another satellite. It was discovered on both sides of the Atlantic simultaneously, on the 19th of September, 1848. Mr. W. C. Bond, employing the splendid 15-inch refractor of the Harvard Observatory, noticed, September 16, a minute star situated in the plane of Saturn's rings.
Of course they form a magnificent object in the night sky of the planet, and it may be that our own zodiacal light is the last vestige of a similar ring, and not an extension of the solar corona. "Saturn has eight moons outside his rings, the nearest, Mimas, being 115,000, and the farthest, Japetus, 220,400 miles from his ball.
Saturn's moons are by no means so interesting to watch as are those of Jupiter. The two largest Titan and Japetus are easily found, and Titan is conspicuous, but they give none of that sense of companionship and obedience to a central authority which strikes even the careless observer of Jupiter's system.
Saturn has perhaps received more than its share of attention owing to these rings. This led to other discoveries. The occasional disappearance of Cassini's Japetus was found on investigation to be due to the same causes as that of Jupiter's fourth satellite, and proves that it always turns the same face to the planet. Uranus and Neptune.
Japetus, the most distant, which revolves at a distance ten times greater than that of the Moon from the Earth, was rising to their left above the edge of the rings, a pale, yellow, little disc shining feebly against the black background of Space. The rest of the eight satellites were hidden behind the enormous bulk of the planet and the infinitely vaster area of the rings.
With the exception of Japetus, they revolve round him in the plane of his rings, and when these are seen edgewise, appear to run along it like beads on a string. "Uranus, the next planet visible, is a pale star of the sixth magnitude, 1,770 million miles from the sun, and completes his round in 84 years.
A beautiful illustration of its quality in this respect was derived by Professor Barnard from an eclipse of Japetus, November 1, 1889. The eighth moon remained steadily visible during its passage through the shadow of the inner ring, but with a progressive loss of lustre in approaching its bright neighbour. There was no breach of continuity.
Saturn's outermost satellite, Japetus, is markedly variable so variable that it sends us, when brightest, just 4-1/2 times as much light as when faintest. Moreover, its fluctuations depend upon its orbital position in such a way as to make it a conspicuous telescopic object when west, a scarcely discernible one when east of the planet.
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