Planet night at Montebello: Discovery of Uranus

by Mark Wagner

Last night at Montebello several of us looked at Uranus and Neptune while waiting for Mars to climb into steadier skies. I mentioned that Uranus is a naked eye object, although down in the soup to the east from our location it would be very difficult. The views through telescopes led a few observers to question my remark, and indeed Uranus did look pretty dim. But today, after a bit of browsing web-pages, I find its magnitude listed anywhere from mag 5.2 to 5.8, challenging from Montebello.

When I mentioned the planet is naked-eye, a discussion ensued regarding the planet's discovery. Who first noticed it? Well, it was Carolyn Herschel and her brother William, on March 13, 1781.

But the real question last night was, if it is at a visual magnitude that can be seen naked eye, why didn't the ancient Arabic, Greek or Chinese astronomers/astrologers discover it? Certainly the other five naked eye planets are brighter and move more rapidly against the stellar background, but I find it amazing that it took until the Herschels visually detecting Uranus' disk in a telescope for the discovery to be made.