Today is special: it is now one full Neptunian year since this giant planet was discovered in 1846!
So today is Neptune’s birthday! Um. Well, kinda.
Yeah, as usual, stuff like this gets complicated. I realized this anniversary was coming up about a year ago, and contacted an old friend about it: Kelly Beatty, editor at Sky and Telescope magazine, who then contacted astronomers John Westfall and Roger Sinnott. We had some fun email exchanges about all this! I think I have a good grip on this now, so let me explain.
The short form
First, to celebrate a birthday, you need the birthdate. That’s the first complication. Neptune was discovered on September 23, 1846 by astronomer Johann Galle using star charts by Johann Encke, and they are generally given credit for it. However, that date of September 23 is a bit dicey! Galle and Encke report that they found Neptune on 9/23 at 12:00:15 "Berlin M.T.", according to Westfall. But they reckoned the day starting at noon! And since they’re using Berlin mean time, you have to account for the longitude of Berlin with respect to 0° longitude on Earth. According to Westfall, once you do all that, you get a discovery time of September 23 at 23:06:40.
Worse yet, there may be some imprecision in the exact time the astronomers reported the discovery, although Galle reported the time to a fraction of a second. Westfall reports that might be as much as 1.2 hours, preferring a discovery time of September 24, 1846 at 00:15 GMT.
Who’s right? Turns out, it doesn’t matter much, since we only need to know the time to within a few hours to get the right date for the birthday. Still, Westfall appears to have looked at this pretty hard, so you know what? Good enough. I’ll use his numbers.
A year by any other name would take as long
OK, so we have the birthdate. Now, how long is a Neptune year?
Yeah, well, that turns out not to be so easy to answer either! Read More