What is the Draconitic Cycle?


In my reading I just came across a mention that the moon has something called the draconitic cycle, or sometimes, the draconitic period (or “draconic” if someone is getting all tense about “draconitic” as a word). The term is a bit of a holdover from medieval astronomy, when everybody was worried all the time that an eclipse might sneak up on them, and so you can see the use in a term which represents how long it takes between successive passages of the moon through its ascending node. Really, it’s amazing they thought they needed to name that at all; surely the idea of successive passages through the ascending node is so common that it barely needs a word, the way we express such concepts as “       ” or “      ” or even “        ” by leaving a gap hanging in our conversations and just waving our arms frantically at people who don’t know what we’re going on about. Anyway, it picked up the name “draonitic cycle” just as you might expect, by astronomers watching the skies night after night to see how long it takes the Moon to be run over by a bicycle, which took until about 1890. Before then bicycles were just those hilarious things with a giant front wheel and a tiny back one that you could ride for parts of a second before tipping over and falling down. The cycles are much quicker these days.