An Account of a Spot Seen in the Sun from the 25th. of April to the 8th. of May Instant, with the Line of Its Course Predicted, If It Make a Second Return, by I. F. Astron. Reg.

An account of a Spot seen in the Sun from the 25th. of April to the 8th. of May instant, with the line of its Course predicted, if it make a second Return, by I.F. Astron. Reg. On the 25th. of April last past, as I was measuring the distance of the Planet & from the Sun, about an hour before Noon I discovered a large Spot entered within his disk a little distant from his following Limb. These appearances however frequent in the days of Scheiner and Galileo, have been so rare of late that this is the only one I have seen in his face since December 1676. Wherefore I thought an account of it might not be unacceptable. By the observed Meridional distances of it and the Sun's Southern Limb from the Vertex at Noon I found it to have $3'40''$ more north declination than the Sun's center, and at $3h.35'$ after Noon I measured its distance from his next Limb $0'40''$. Next morning April 26, I saw it more remote from his Limb, and by the Observations then made (at 8 h. mane) determined its Longitude from the Sun's Axis $66\frac{1}{2}$ deg. and its declination from the Solar Equator $9\frac{1}{2}$ d.g. South. Whence supposing the Revolution of any point of the Sun to the same fixed Star to be performed in 25 days 6 hours, the Angle of his Aequator and our Ecliptick 7 degrees, and the Longitude of his northern Pole $16\frac{1}{2}$ deg. I designed the Line of its Way or trace over the Sun and the Points in it where the Spot would appear every morning after at the same hour, till its egress on the 8th. of May, as in the Figure, which I found altogether confirmed by such Observations as I made till then, so that I had no reason to doubt of the Theory. When the Spot was near the middle of the Sun it appeared very broad and almost square, the Nucleus of the same Figure about 40" diameter, shaped as it is designed in the lower part of the Scheme, but when it was near the Limb much narrower and almost Oval, it seemed to have Confidence enough to endure a second return, if it shall it will enter the visible disk of the Sun on the 21 of May in the evening, and its passage over him describe a line nearly straight with greater latitude from the Ecliptick, as I have designed it in the Figure, wherein you will see its place every morning at 8 a Clock till its exit the 4th of June about Sun rise. Advertisement. The Anachronism committed in placing this paper in the Transaction of March was occasion'd by the necessity of its coming forth early, and there being no room for the Diagram belonging to it, in the Plate of the following Transaction, which was provided before the arrival of the discourse.