msb@sq.sq.com (Mark Brader) (07/22/89)
> Neptune was discovered in 1846, and the planet takes 165 years to > orbit the Sun; thus, Neptune won't return to the position where > astronomers first saw it until 2011. This leaves great uncertainty in > the precise knowledge of Neptune's orbit ... Actually this isn't quite true. Several astronomers saw Neptune before it was discovered, recording it as a star each time. The first of them was Galileo, who was watching satellites of Jupiter at the time. He didn't have any way of accurately measuring positions of celestial objects, but he did record the positions in relation to Jupiter of whatever stars it was near at the time. One night he found that one of them wasn't in the place he'd last put it down-- And he assumed he'd made a mistake, and it happened that he did not get another look at Jupiter until Neptune was too far away from it to see. This was all written up in Scientific American a few years ago, and it was also noted that the position implied by Galileo's notes did not match the current knowledge of Neptune's orbit. Perhaps the Voyager II observations will help resolve this. Or perhaps not. This article is crossposted to sci.astro and sci.space, with followups directed to sci.astro. This article is in the public domain. -- Mark Brader, SoftQuad Inc., Toronto, utzoo!sq!msb, msb@sq.com MARTIANS BUILD TWO IMMENSE CANALS IN TWO YEARS. Vast Engineering Works Accomplished in an Incredibly Short Time by Our Planetary Neighbors. -- N.Y.Times headline, August 27, 1911