April 17 – Method to the madness

Today’s Factismal: Earth is the only planet that does not have a system for naming its features.

If you’ve ever looked at the Moon or at pictures of Mars or the other planets, then you’ve probably noticed that there is a peculiar rhythm to the names. For example, all of the large, dark blotches on the Moon are called “Mare Something” (Mare Frigoris, Mare Tranquilitatis, Mare Insularum) and all of the craters are named after scientists and explorers (DaVinci Crater, Tycho Crater, humboldt Crater). Similarly, all of the features except one on Venus are named after women. And all of the moons of Jupiter are named after the many,, many paramours that Jupiter (Zeus) had.

Scientists use these conventions because it makes it easier to remember both what you are looking at and where it is. “Maat mons? That’s an Egyptian goddess so it must be a mountain on Venus.” “Rhea? That’s one of the titans, so it must be a moon of Saturn.” But what even scientists sometimes forget is where the system got its start.

The Moon, with Mare Imbrium and Mare Frigorum clearly visible (My camera)

The Moon, with Mare Imbrium and Mare Frigorum clearly visible
(My camera)

It all happened in 1665, just 33 years after Galileo had been convicted of heresy for promoting the idea that the Earth moved around the Sun instead of the other way around. A Catholic priest by the name of Giovanni Riccioli who was a fan of Galileo’s methods but not of his ideas was busy using the telescope (which Galileo invented) to look at the Moon. He agreed that Galileo was right when he said that the Moon’s surface wasn’t perfect; that it was covered with blotches and pockmarks. And the thought that Galileo was wrong when he said that the Earth went around the Sun (Giovanni, like all good Jesuits at the time, held that things were the other way around). But how could the new features on the Moon be described to other astronomers across the globe? With a map.

So Giovanni spent quite a few late nights staring at the Moon and drawing a detailed map of its surface. But Giovanni wasn’t satisfied to just make a pretty image; instead, he wanted to provide a way for people to know that they were all talking about the same thing when they said “that big bright blotch on the bottom left”, so Giovanni named the things that he saw on the surface of the Moon. Because the big dark blotches looked like they were full of water (spoiler: they weren’t), he named them “mares”, which is Latin for “seas”. And he named the different seas after the different nymphs. He then named the smaller dark blotches after lakes (“lacus”), inlets (“sinus”), and marshes (“paludes”).  So by looking at the first part of the name, a scientist will always know about how big the object is. And by looking at the second part, a scientist has an idea of where on the Moon it is.

Giovanni then went a step further and named the craters that he could see. But, being a Jesuit, he had to include a little joke in the names. Just as Michelangelo painted his enemies in Hell, Giovanni used the names of those who supported the heliocentric universe for the craters nearest Oceanus Procellarum (the largest of the mare and the only “oceanus” or ocean on the Moon); if you don’t get the joke, it is because you haven’t yet realized that Oceanus Procellarum means “Ocean of Storms”.

Though Giovanni named as many of the features as he could see, his telescope wasn’t very good. But today, we have much better telescope and even spacecraft orbiting the Moon, sending back lots of high quality pictures of the surface. And you can use those images to identify and name things on the Moon. If you’d like to take part, then head on over to the Moon Zoo:

One thought on “April 17 – Method to the madness

  1. Pingback: December 31 – The Year In Science | Little facts about science

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