Basel and Solothurn, Switzerland — 9 August 1762
Slow-flying spindle in the Sky
Two witnesses at separate observatories (Rostan in Basel and Croste in Solothurn) reported a vast spindle-shaped cigar in slow flight in front of the Sun. Monsieur de Rostan, an astronomer and member of the Medicophysical Society of Basel, Switzerland, observed the object with the aid of a telescope as it eclipsed the sun. This object could be observed daily for almost a month from Lausanne and also by a second astronomer in Sole, near Basel. Monsieur de Rostan traced its outline with a camera obscura and sent the image to the Royal Academy of Sciences in Paris. The drawing has not been preserved, unfortunately, but there is no doubt that it once existed and was regarded with some amazement. As this is historically an important incident the original report is produced in full below: An account of a very singular phenomenon seen in the disk of the sun, in different parts of Europe, and not in others. “The 9th of August, 1762, M. de Rostan, of the economic society at Berne, of the medico-physical society at Basle, while he was taking the sun’s altitudes with a quadrant, at Lausanne, to verify a meridian, observed that the sun gave but a faint pale light, which he attributed to the vapours of the Leman lake; however, happening to direct a fourteen foot telescope, armed with a micrometer, to the sun, he was surprised to see the eastern side of the sun, as it were, eclipsed about three digits, taking in a kind of nebulosity, which environed the opaque body, by which the sun was eclipsed. “In the space of about two hours and a half, the fourth side of the said body, whatever it was, appeared detached from the limb of the sun; but the limb, or, more properly, the northern extremity of this body, which had the shape of a spindle, in breadth about three of the sun’s digits, and nine in length, did not quit the sun’s northern limb. This spindle kept continually advancing on the sun’s body, from east towards west, with no more than about half the velocity with which the ordinary solar spots move; for it did not disappear till the 7th of September, after having reached the sun’s western limb. “M. Rostan, during that time, observed it almost every day; that is to say, for near a month; and, by means of a camera obscura, he delineated the figure of it, which he sent to the royal academy of sciences at Paris. “The same phenomenon was observed at Sole, in the bishopric of Basle, situated about five and forty German leagues northward of Lausanne. M. Coste, a friend of M. de Rostan, observed it there, with a telescope of eleven feet, and found it of the same spindlelike form, as M. de Rostan, only it was not quite so broad; which, probably, might be owing to this, that growing near the end of its apparition, the body began to turn about, and present its edge. “A more remarkable circumstance is, that at Sole it did not answer to the same point of the sun as it did at Lausanne: it therefore had a considerable parallax: but what so very extraordinary a body, placed between the sun and us, should be, is not easy to divine. It was no spot, since its motion was greatly too slow; nor was it a planet or comet, its figure seemingly proving the contrary. In a word, we know of nothing to have recourse to in the heavens, whereby to explain this phenomenon; and, what adds to the oddness of it, M. Messier, who, constantly observed the sun at Paris during the same time, saw nothing of such an appearance.”
Source: “Natural History: An Account of a Very Singular Phenomena Seen in the Disk of the Sun, in Different Parts of Europe, and Not in Others,” Annual Register 9 (1766): 120-121. Case: W302