261. Jupiter without Satellites.—It occasionally happens that every one of Jupiter's satellites will disappear at the same time, either by being eclipsed or occulted, or by being in transit. In this event, Jupiter will appear without satellites. This occurred on the 21st of August, 1867. The position of Jupiter's satellites at this time is shown in Fig. 284.
Fig. 284.
Saturn.
THE PLANET AND HIS MOONS.
262. The Orbit of Saturn.—The orbit of Saturn is rather more eccentric than that of Jupiter, its eccentricity being somewhat more than one-twentieth. Its inclination to the ecliptic is about two degrees and a half. The mean distance of Saturn from the sun is about eight hundred and eighty million miles. It is about a hundred million miles nearer the sun at perihelion than at aphelion.
263. Distance of Saturn from the Earth.—The mean distance of Saturn from the earth at opposition is eight hundred and eighty million miles minus ninety-two million miles, or seven hundred and eighty-eight million; and at conjunction, eight hundred and eighty million miles plus ninety-two million, or nine hundred and seventy-two million. Owing to the eccentricity of the orbit of Saturn, his distance from the earth at opposition and at conjunction varies by about a hundred million miles at different times; but he is so immensely far away, that this is only a small fraction of his mean distance.
264. Apparent Size and Brightness of Saturn.—The apparent diameter of Saturn varies from about twenty seconds to about fourteen seconds. His apparent size at his extreme and mean distances from the earth is shown in Fig. 285.
Fig. 285.