Galileo Galilei sighted the planet Neptune a second time, unknowingly. It was discovered only in 1846 by the Berlin Observatory, based on the indications provided by Adams and le Verrier. He noted its position, changed from January 6th, in a different color of ink on a piece of paper, which was found much later. It’s unknown what happened next, but Galileo probably forgot about it, and in any case, he never published anything about it. One can only imagine how history would have changed if we had discovered Neptune two and a half centuries earlier, even before Uranus. On December 27, 1612, Galileo drew the positions of Europa, Ganymede, and Callisto in surprising agreement with the JPL ephemeris, and also drew a dotted line that extended to the margin of the paper, where he wrote “fixa” (fixed star). The line indicated that the object was visible in the telescope’s field of view, but it could not be made to fit within the margins of the paper, with a scale representation. According to the ephemeris consulted by Kowal and Drake, Neptune was close to stationary, with a magnitude of 7.8 m, easily within the range of Galileo’s instrument, and was also located in the extension of the line drawn by Galileo, at a distance of 41 Jovian radii. Although the astronomer did not record his distance, the identification of the fixa with Neptune proved reliable, because examination of modern star charts showed that there was no fixed star observable through a telescope in that area of the sky. From December 28th to January 1st, the sky was too overcast to allow reliable observations. On January 28th, around 11:00 a.m., Galileo marked the position of the planet that would be discovered over two centuries later, Neptune, creating a complex drawing.
