Neptune Photo:NASA/JPL

On Sept 23-24, 1846, the planet Neptune was discovered by by Johann Gottfried Galle. In celestial terms, that was 165 years ago. In terms of Neptune’s path around the Sun it was only about one year ago. (To be precise, on July 12th, Neptune completed one full circuit around the Sun since its discovery.) So Happy Birthday Neptune. We can celebrate Neptune’s second rotation since discovery in 2176. I can hardly wait.

Happy Birthday, Neptune!

Neptune’s discovery is one of the most remarkable stories in astronomy history. The planet’s existence had been predicted due to its gravitational perturbation of Uranus’s orbit, and Neptune was actually found just a degree from its predicted position. But it turns out that this remarkable accuracy was due, in some sense, to luck as much as skill. You can read the whole story in our July issue.

This is an awkward time to observe Neptune; it doesn’t reach a reasonable height above the horizon until the wee hours of the morning. Moreover, it won’t appear anywhere near its discovery position with respect to the stars, due to the fact that Earth is in quite a different part of its orbit. But if you want to view Neptune anyway, it’s easy to do with decent telescopes and binoculars. You will need a good planetarium program or our online observing guide and charts.