Astronomical Curiosities: Facts and Fallacies. Gore John Ellard

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СКАЧАТЬ curious observations have been recorded with reference to Jupiter’s satellites; some very difficult of explanation. In 1711 Bianchini saw satellite IV. so faint for more than an hour that it was hardly visible! A similar observation was made by Lassell with a more powerful telescope on June 13, 1849. Key, T. T. Smyth, and Denning have also recorded unusual faintness.134 A very remarkable phenomenon was seen by Admiral Smyth, Maclear, and Pearson on June 26, 1828. Satellite II., “having fairly entered on Jupiter, was found 12 or 13 minutes afterwards outside the limb, where it remained visible for at least 4 minutes, and then suddenly vanished.” As Webb says, “Explanation is here set at defiance; demonstrably neither in the atmosphere of the earth, nor Jupiter, where and what could have been the cause? At present we can get no answer.”135 When Jupiter is in opposition to the sun – that is, on the meridian at midnight – satellite I. has been seen projected on its own shadow, the shadow appearing as a dark ring round the satellite.

      On January 28, 1848, at Cambridge (U.S.A.) satellite III. was seen in transit lying between the shadows of I. and II. and so black that it could not be distinguished from the shadows, “except by the place it occupied.” This seems to suggest inherent light in the planet’s surface, as the satellite was at the time illuminated by full sunshine; its apparent blackness being due to the effect of contrast. Cassini on one occasion failed to find the shadow of satellite I. when it should have been on the planet’s disc,136 an observation which again points to the glowing light of Jupiter’s surface. Sadler and Trouvelot saw the shadow of satellite I. double! an observation difficult to explain – but the same phenomenon was again seen on the evening of September 19, 1891, by Mr. H. S. Halbert of Detroit, Michigan (U.S.A.). He says that the satellite “was in transit nearing egress, and it appeared as a white disc against the dark southern equatorial belt; following it was the usual shadow, and at an equal distance from this was a second shadow, smaller and not so dark as the true one, and surrounded by a faint penumbra.”137

      A dark transit of satellite III. was again seen on the evening of December 19, 1891, by two observers in America. One observer noted that the satellite, when on the disc of the planet, was intensely black. To the other observer (Willis L. Barnes) it appeared as an ill-defined dark image.138 A similar observation was made on October 9 of the same year by Messrs. Gale and Innes.139

      A “black transit” of satellite IV. was seen by several observers in 1873, and by Prof. Barnard on May 4, 1886. The same phenomenon was observed on October 30, 1903, in America, by Miss Anne S. Young and Willis S. Barnes. Miss Young says —

      “The ingress of the satellite took place at 8h 50m (E. standard time) when it became invisible upon the background of the planet. An hour later it was plainly visible as a dark round spot upon the planet. It was decidedly darker than the equatorial belt.”140

      The rather rare phenomenon of an occultation of one of Jupiter’s satellites by another was observed by Mr. Apple, director of the Daniel Scholl Observatory, Franklin and Marshall College, Lancaster, Pa. (U.S.A.), on the evening of March 16, 1908. The satellites in question were I. and II., and they were so close that they could not be separated with the 11·5-inch telescope of the Observatory.141 One of the present writer’s first observations with a telescope is dated May 17, 1873, and is as follows: “Observed one of Jupiter’s satellites occulted (or very nearly so) by another. Appeared as one with power 133” (on 3-inch refractor in the Punjab). These satellites were probably I. and II.

      Jupiter has been seen on several occasions apparently without his satellites; some being behind the disc, some eclipsed in his shadow, and some in transit across the disc. This phenomenon was seen by Galileo, March 15, 1611; by Molyneux, on November 12, 1681; by Sir William Herschel, May 23, 1802; by Wallis, April 15, 1826; by Greisbach, September 27, 1843; and by several observers on four occasions in the years 1867-1895.142 The phenomenon again occurred on October 3, 1907, No. 1 being eclipsed and occulted, No. 2 in transit, No. 3 eclipsed, and No. 4 occulted.143 It was not, however, visible in Europe, but could have been seen in Asia and Oceania.[144] The phenomenon will occur again on October 22, 1913.144

      On the night of September 19, 1903, a star of magnitude 6½ was occulted by the disc of Jupiter. This curious and rare phenomenon was photographed by M. Lucien Rudaux at the Observatory of Donville, France.145 The star was Lalande 45698 (= BAC 8129).146

      Prof. Barnard, using telescopes with apertures from 5 inches up to 36 inches (Lick), has failed to see a satellite through the planet’s limb (an observation which has been claimed by other astronomers). He says, “To my mind this has been due to either poor seeing, a poor telescope, or an excited observer.”147 He adds —

      “I think it is high time that the astronomers reject the idea that the satellites of Jupiter can be seen through his limb at occultation. When the seeing is bad there is a spurious limb to Jupiter that well might give the appearance of transparency at the occultation of a satellite. But under first-class conditions the limb of Jupiter is perfectly opaque. It is quibbling and begging the question altogether to say the phenomenon of transparency may be a rare one and so have escaped my observations. Has any one said that the moon was transparent when a star has been seen projected on it when it ought to have been behind it?”

      Prof. Barnard and Mr. Douglass have seen white polar caps on the third and fourth satellites of Jupiter. The former says they are “exactly like those on Mars.” “Both caps of the fourth satellite have been clearly distinguished, that at the north being sometimes exceptionally large, covering a surface equal to one-quarter or one-third of the diameter of the satellite.”148 This was confirmed on November 23, 1906, when Signor J. Comas Sola observed a brilliant white spot surrounded by a dark marking in the north polar region of the third satellite. There were other dark markings visible, and the satellite presented the appearance of a miniature of Mars.149

      An eighth satellite of Jupiter has recently been discovered by Mr. Melotte at the Greenwich Observatory by means of photography. It moves in a retrograde direction round Jupiter in an orbit inclined about 30° to that of the planet. The period of revolution is about two years. The orbit is very eccentric, the eccentricity being about one-third, or greater than that of any other satellite of the solar system. When nearest to Jupiter it is about 9 millions of miles from the planet, and when farthest about 20 millions.150 It has been suggested by Mr. George Forbes that this satellite may possibly be identical with the lost comet of Lexell which at its return in the year 1779 became entangled in Jupiter’s system, and has not been seen since. If this be the case, we should have the curious phenomenon of a comet revolving round a planet!

      According to Humboldt the four bright satellites of Jupiter were seen almost simultaneously and quite independently by Simon Marius at Ausbach on December 29, 1609, and by Galileo at Padua on January 7, 1610.151 The actual priority, therefore, seems to rest with Simon Marius, but the publication of the discovery was first made by Galileo in his Nuncius Siderius (1610).152 Grant, however, in his History of Physical Astronomy, calls Simon Marius an “impudent pretender”! (p. 79).

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