Back in the good ol’ days of the ancient Greeks there were only 48 constellations, or sky figures, and they were only intended to signify general patches and star patterns in the sky, not strictly-defined regions. There were those wonderful mythological characters such as Sagittarius the Archer, Cassiopeia the Queen-in-a-Chair, Cepheus the King-in-a-Doghouse (well, it looks like that, anyhow), Orion the Hunter, and Hercules the Hunk. There were creatures such as Delphinus the Dolphin, Cancer the Crab, Aries the Ram, and Capricornus the Sea-Goat (whatever the heck that is). Some figures overlapped and shared parts of each other: Andromeda the Chained Maiden also shared part of the foreleg of Pegasus the Flying Horse. Serpens was clutched in the middle by Ophiuchus the Serpent-Bearer (what else were you going to call him?), but a star in the middle of the snake belonged to . . . who? And then there were vast chunks of the sky needed to make up just one lousy constellation, like Argo Navis, the ship of Jason’s Argonauts.
Then, in 1519, Ferdinand Magellan took his ship south to circumnavigate the globe, and encountered vast new realms of the sky that had never been seen before from Europe or North Africa. Within a century, celestial mapmakers had gone into a frenzy, creating all sorts of new celestial doodads to clutter up the heavens. They drew upon the latest and greatest in technology to fill in and name those starry voids: Telescopium the Telescope, Microscopium the Microscope, Horologium the Clock, Sextans the Sextant, Fornax the Lab Furnace, and, most wondrous of all, Antila the Air Pump. (If this had happened instead in more recent times, imagine the astral mess we would have with the likes of the Space Shuttle, the Frigidaire, the Television, and the Playstation III.) Poor Ferdinand didn’t get any constellations of his own, but he did get a couple of nice star fields, now known to be neighboring galaxies, named for him: the Large and Small Magellanic Clouds.
By the 17th century, celestial cartographers such as Johann Bayer had decided to organize the heavens and started naming stars according to their relative brightness within a constellation: the alpha star, beta star, gamma, delta, and so on. Others like John Flamsteed started numbering the stars–one, two, three–within a constellation. But whose constellation owned which star? And what about that vast and cumbersome Argo? Well, break that ship up on the rocks into three new pieces: Carina the Keel, Vela the Sails, and Puppis the Poop Deck.
Imagine the confusion when an astronomer wanted to talk about a particular star, but nobody knew exactly what it was called or what constellation it belonged to. Believe it or not, it wasn’t until 1930 that the issue was finally settled once and for all, when the International Astronomical Union (IAU) came to the rescue and settled upon an official list of 88 constellations, and exactly where the boundaries of each started and stopped in the sky. (These are the same folks, by the way, who gave you Pluto-Is-Not-A-Planet in 2006. It’s a dirty job, but somebody’s got to do it.)
Anyway, the boundary lines were drawn, all nice and neat along lines of right ascension and declination in the sky (just like lines of longitude and latitude on the Earth). Every star belongs to, and resides within, a specific constellation, just like every town belongs to and lies within a state. The sky was chopped up into square-ish zigs and zags along the coordinate lines, just like Colorado is a nice, neat, boring rectangular shape (but curving nicely to fit a spherical Earth). Fortunately, the sky doesn’t have squiggly natural boundaries like coastlines, meandering rivers, or mountain ridges to mess up its demarcations. It’s just a bunch of straight lines neatly arranged to line up with the Earth’s poles and equator. Simple, right?
Well, not so much. There’s this thing called The Age of Pisces and the dawning of the Age of Aquarius. The Earth wobbles (precesses) on its axis, so any nice alignment of those sky boundaries with the Earth’s axis of rotation can only be valid for one moment in time. In 1930, the IAU decided–for some reason–that the time for when such alignment applied would be the year 1875. So, even from the very beginning, the boundaries have been skewed cattywampus. But never fear, in slightly less than 26,000 years, things will return to being nice and square–for a moment.
Of course, by then, some of those stars that were in a certain constellation will have emigrated across the border into an adjacent constellation (astronomers call it “proper motion”) and the naming problems will be faced anew.
We’ll let the IAU worry about that when the time comes. For now: 88 constellations, no overlaps, no gaps. Nice and neat.