Thursday, January 12, 2012

Conventional Constellations

I haven't been up to posting anything for the last few days due to a raging cold and some exhaustion after my friend's wedding, but recently I came across a list of constellations no longer officially recognized by the International Astronomical Union (IAU), and thought I'd share some of the more amusing ones with you.

To a modern astronomer, the word "constellation" has a very specific meaning: it's a region of the celestial sphere as formalized by the IAU in 1922. Nowadays, there are 88 official constellations, formed so that between them they cover the entire night sky so that any celestial object may unambiguously be found to be located in one or another of them.

Prior to 1922, this was not the case. There was no standard set of constellations, so different authors could (and did) publish star charts with their own favorite constellations on them. Since many of the authors came from different European states at a time when patriotism and national identity were on the rise, you can imagine that there was a bit of one-upping and brinkmanship going on between various star chart publishers. An example of such was Robur Carolinum, Charles' Oak, named in honor of the tree where Charles II of England is said to have hidden from Oliver Cromwell's troops after the Battle of Worcester, which was put on the map by Sir Edmund Halley, of eponymous comet fame. Other examples were Frederici Honores, Frederick's Honors, created to honor Frederick II of Prussia, and Psalterium Georgii, George's Harp, in honor of  George III of Britain (yes, the one who ended up losing the American colonies). See a bit of a trend? Actually, though, these kind of overt advances were fairly rare, and most of the proposed constellations were much more neutral in tone.

Even though they may not all have been national-glory-seeking advances, many of the constellations proposed in the 18th and 19th centuries were mutually incompatible because they incorporated stars used by constellations in other star charts. But to fully understand why people were making up constellations in the first place, it is necessary for me to back up and show how the original constellations came about.

Human beings are wired to look for patterns everywhere, and there have been recorded patterns in the stars for thousands of years. The earliest recorded star catalogs that we know of belonged to the Babylonians; the Three Stars Each catalog appear to have been recorded around the 12th century BC (near the boundary between the Late Bronze Age and the Iron Age, sometime during the period of the Judges in the Biblical chronology). After this, perhaps sometime around 1000 BC, the MUL.APIN catalog was compiled using more accurate observations.

(For the curious, MULAPIN refers to the first constellation of the Babylonian year, "The Plough" [not associated with the asterism known by the same name in Britain, which is usually known as the Big Dipper in North America]. The difference between an asterism and a constellation is fairly subtle. An asterism is just any pattern in the stars. A constellation, as mentioned before, is one of the 88 officially-recognized patches of sky that contains a particular asterism. So the Big Dipper is technically not a constellation but an asterism, located in the constellation of Ursa Major which contains additional stars and whatnot.)

The Babylonians weren't the only ones coming up with patterns in the sky, however. The ancient Chinese came up with their own system of constellations, as did the ancient Indians, the Mayans, and the Polynesians. In the southern hemisphere where the Milky Way is more visually striking, both the Inca and the Aborigines came up with constellations composed not of stars, but of dark nebulae in the Milky Way.

After the conquest of the former Persian empire by Alexander the Great in the 4th century BC, Babylonian astronomical knowledge became available to the Greek-speaking world which adopted it readily. In the 2nd century BC an otherwise little-known individual by the name of Claudius Ptolomy, a Roman-era scholor in Egypt, wrote what ranks right up there among the most influential scientific texts of all time: the Almagest. (The origin of the name is a fascinating aside: the original name in Greek meant "Mathematical Treatise", which became "The Great Treatise" [not undeservedly] and eventually just something like "The Greatest", which sounds like magisti in the Greek of the time, which the Arabs transliterated as al-majisti when they preserved the ancient Greek writings in the Middle Ages, and which was taken into English [finally] as Almagest.  Phew.)

The Almagest is a fascinating piece of work for many reasons (not least of which being that it helped set up the Aristotelian geocentric cosmology that was to reign in astronomy for the next 1800 years), but for our purposes the most interesting part of it is that it formalized a system of 48 constellations. Twenty of these were taken directly from the Babylonian system, while another ten had the same stars but different names. What's interesting is that all but one of these constellations have survived to the present day, as official IAU-sanctioned constellations (and the single one that wasn't, Argo Navis the Argonaut's Ship, was simply broken up into three separate constellations because it was considered "too big". It now exists as Vela, the Sails, Carina, the Keel, and Puppis, the poop deck).

This long, roundabout treatise on the history of constellations is mostly to give you a feel for how they have changed (and how they haven't) through most of history. In the 17th to 19th centuries there was a huge explosion in the number of new constellations being added to star charts. You see, due to his location, Ptolemy couldn't see below a certain southern declination, so he had no constellations for the area around the south celestial pole. Likewise, he didn't bother filling in every area of the sky with a constellation, leading to bare patches even in the northern hemisphere. After the invention of the telescope and the explosion of new objects found in the centuries that followed, astronomers naturally wanted an easy way to roughly locate where something was on the sky, akin to being able to give the state a particular city is located in, rather than having to come up with the exact latitude and longitude all the time. This state of affairs led to people trying their hand at coming up with new constellations to both fill in the gaps left by Ptolomy and to create new constellations where he had never set eye. To make a long story short: some were successful, others not so.

And that's what I originally wanted this much-longer-than-anticipated post to be about: constellations that just didn't make it. The "also rans". They are objects of historical interest, and some of them are just plain funny. Looking over the list, one name in particular stands out as the source of amusing constellations, an English botanist (of all things) by the name of John Hill, who introduced constellations representing the Seahorse, Toad, Leech, Slug, Earthworm, Limpet, Mussel, Rhinoceros Beetle, Eel, Long-legged Spider, Tortoise, Star-Gazer Fish, and two species of extinct mollusk. He even introduced one representing the Pangolin, which just might be my favorite animal, and which I kinda feel bad now isn't an official constellation. Oh, well, not much to do about it. Now that the sky has been officially divided among the 88 official constellations, there's no more room for someone to create their own versions and market them, except for fun. Which isn't bad, really, science needs order and stability to flourish, and an internationally-agreed-upon map of the entire sky has been quite beneficial to astronomy overall.

And with that I think I need to end this rambling post, seeing as it's gone way beyond what I meant when I started, and get some sleep. A hui hou!

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