In the next days we mark an anniversary of a discovery made in 1978 that wasn't exactly an earthshaker, but is an interesting look into astronomy, nonetheless.

You may recall that Pluto was discovered in 1930 by a young astronomer Clyde Tombaugh. He noticed that in several images of a particular part of the sky taken some time apart that the stars were stationary as expected, but that there was a small dim dot moving slowly through them. Long story short: It was Pluto.

Those were more simple times, when a new spherical body in space found in an orbit all by itself would just naturally be christened a new planet, no questions asked. And it was a time when a body revolving around a planet would just naturally be called its moon.

Well, in 1978, on 22 June to be exact, astronomer James Christy noticed that the best images we could get of Pluto back then periodically showed a slight bulge. It turns out that that bulge was not the result of crummy photography, but was really a small spherical body circling Pluto. Christy had discovered a wee moon around tiny Pluto!

Legend has it that he named the new moon Charon, after his wife Charlene, whom people called "Char" for short. This kind of went against the tradition of naming heavenly bodies after Greek or Roman mythological beings. But lucky him, Charon was also the name for the mythical boatman on the river Styx, the one who ferried souls off to Hades. So Charon stuck.

There they were, Pluto and Charon, planet and moon, living happily together. Until recently that is.

You may recall that Pluto has had some problems lately among astronomers. It was demoted from planet to... well, all kinds of things: dwarf planet, transneptunian object, Kuiper Belt Object.

If Pluto is a dwarf planet then it might follow that Charon is just a moon of a dwarf planet. But - surprise! - it is more complicated than that.

Pluto and Charon are both pretty similar in size, so much so that Charon doesn't really go around Pluto like the Moon around us - a little guy circling about a barely moving big guy. Pluto and Charon's mutual center of gravity is somewhere between the two in space. They are more like two people holding hands and spinning around and around some common center between them, rather than like a stationary person swinging a ball around on a string.

This is disturbing enough for some astronomers that Charon and Pluto are being looked at as a possible dwarf planet duo.

What is Charon's status at the moment? It is still a moon by most accounts, at least until the International Astronomical Union officially defines what a large moon of a dwarf planet is. Sheesh!

O, for the simpler days when there were but mere "planets" and "moons"!