it's the first anniversary ...

... of the discovery of Neptune. Measured in Neptunian years, that is. Neptune was discovered on September 23, 1846, by astronomers who were actually looking for it. Discrepancies in the orbit of Uranus had been hypothesized to be caused by the gravity of another planet. Some astronomers calculated where in the sky such a planet might be, and others looked for it, and sure enough, found a tiny dot of light among the stars that wasn't on the charts and that moved predictably by tiny increments from night to night.

According to the NASA fact sheet, Neptune has a sidereal orbit (orbit as measured against the background stars) of 60,189 Earth days, and, if I've counted up correctly, the anniversary point is ... tomorrow, July 9, 2011. We've now tracked it all the way around past its background stars exactly once, and that completes the known major planets for the first time since Uranus was discovered.

So let us celebrate this rare conjunction of events and wish happy birthday, then, to Neptune.