“Planet” is a wandering word – Magazine ?

The terms we use to express scientific knowledge have to be redefined as it advances. This is what has happened to the word “planet” for millennia.

Go to ancient Greece, tell a Greek that we live on a planet and you will see that he sends you to the asylum. And rightly so. It is not because the Greek is stupid and does not know. It is not that we are revealing to him knowledge that was too advanced for his time. It’s simply that “planet” meant something totally different 2,300 years ago.

walkers

At some point in primary or secondary school one learns that “planet” means “wanderer” in Greek… and he stays there because the word doesn’t mean anything to him. After several decades of knowing that “planet” was “wandering,” a few years ago I gave a class on Johannes Kepler at the Juriquilla campus. One of the participants was Greek and I took the opportunity to ask her what “planet” means in her language. She replied that the corresponding verb in modern Greek means “to walk.”

It remains to be known why the Greeks thought that the planets walked. If one looks at the sky innocently but carefully, as humans did in many places in remote times, after a while one will distinguish two types of lights in the sky: those that rotate together around the world, always forming the same patterns on the sky. celestial vault—the constellations—and those that, in addition to rotating with everything else, move on that backdrop, changing their relative position among themselves and with respect to the constellations. Abstracting from the daily rotation of the celestial vault, the most natural thing is to call them “lights that do not move (fixed)” and “lights that do move (wandering)”, and that is what the ancient Greeks did, although in Instead of lights they named them “astros” or “stars.”

We have to struggle a little with our 21st century knowledge to understand that for the Greeks the Sun was also a planet. We have to think about it like this: if its brightness did not overshadow the stars, we would see that the Sun also moves between the constellations, and therefore is a wandering star in the ancient Greek sense. And the Moon too. Thus, in the Greek skies the planets were Mercury, Venus, the Moon, the Sun, Mars, Jupiter and Saturn (the other planets that we know today can only be seen with a telescope and therefore were not known to the Greeks). Nothing to do with our modern concept, according to which a planet is a world that revolves around a sun (I don’t want to write “star” because that word didn’t mean the same thing as today).

And what has the Earth been in this gibberish? The Earth was the habitable part of the Universe (which in those times was called the world, to the greater confusion of humans in the 21st century): a sphere located in the center of everything, on whose surface humanity lived and around which they revolved. the stars—the fixed ones and the wandering ones. If one day you travel back in time to ancient Greece, avoid calling Earth a “planet.” To the ancient Greeks it would sound as absurd as it does to us that the Greek tells us that the Sun is a planet. And yet, both we and the Greek are right. “Planet” is a wandering word that has changed its meaning over the centuries to adjust to what we are finding out about the Universe.

Revolution

Nicolás Copernicus is famous because he has a statue in Chapultepec and also because he was the first to say that the Earth revolves around the Sun and they listened to him (he was the first to say it to whom they paid attention; There were others who said it before, but they did not substantiate it so well and they were ignored). And he said it in a little book in which he carefully constructed the argument in favor of this idea. I’ll spare you the details.

Once they paid attention to Copernicus, many years after his death, and everyone became convinced that the Earth was not fixed in the center of the cosmos, but rather revolving around the Sun, a conceptual tidal wave occurred with the word “ planet”. If the Earth revolves around the Sun as we now know Mercury, Venus, Mars, Jupiter and Saturn do, then the Earth is like a wandering star. And if the Earth is like the wandering stars, then these are like the Earth. Therefore, the planets are not simple little lights in the sky: they are other worlds, other spheres of considerable size and possibly inhabited. It was even thought that they had to be inhabited. The argument is very well illustrated by this paragraph that I love from the article “Astronomy” from the first edition of the Encylopaedia Britannica (1771): “On the surface of the Moon, because it is closer than any other celestial body, we see a greater resemblance to the Earth. With the help of telescopes we see that the Moon is full of high mountains, extensive valleys and deep cavities. These similarities leave no doubt that all the other planets and moons in the system are designed to house creatures with the capacity to know and worship their beneficent Creator.” It was a very common argument at the time: these new worlds were also the work of God, and since God does nothing in vain—and since those worlds are clearly not for us—, they must be for their own inhabitants, who (there would be no shortage of more) will necessarily be intelligent and will worship their creator.

So, in addition, the Copernican revolution opened the doors to the concept of inhabitants of other planets, but that is another story.

The new one in the colony

The word “planet” kept wandering. In 1610, Galileo Galilei discovered four little stars orbiting Jupiter with his telescope and called them “Medicean planets” in honor of the Medici family, rulers of his native Tuscany. Who knows when, after Galileo, objects that revolved around larger objects like the Medicean planets around Jupiter or the Moon around the Earth stopped being called planets and were called satellites or moons. At the beginning of the 19th century, when previously unknown objects began to appear between the orbits of Mars and Jupiter, they were also called planets for a time, until there were so many that it was uncomfortable, and to refer to them the astronomer William Herschel invented the word “asteroid”, which means “star-like”. Herschel chose this name because the asteroids were so small that in the telescope they looked like pinpoints of light, just like distant stars.

Then Pluto appeared. When astronomer Clyde Tombaugh found it in 1930, the most natural thing was to include it among the planets. It was an object that revolved around the Sun, and the discovery was also the culmination of the search for a hypothetical “planet X”, which began after the discovery of Neptune 100 years earlier. This search went through several stages, including one in which Urbain Leverrier, the discoverer of Neptune, searched for planet X between the Sun and Mercury. Leverrier referred to his hypothetical intra-Mercurian planet as Vulcan, the name of a Roman god associated with the tremendous heat it would be on that planet because it was so close to the Sun. Tombaugh worked at the Lowell Observatory, founded by millionaire Percival Lowell to study the mythical channels of Mars and to find planet X. This ended up appearing, but nothing about channels. They were a chimera, as Planet X may well have been.

Adding a member to the list of planets was nothing from the other Thursday. It had already happened in 1781 with the discovery of Uranus, in 1801 with the discovery of Ceres (the first asteroid, originally considered a “missing” planet between Mars and Jupiter) and in 1846 with the discovery of Neptune. After Tombaugh’s discovery, a contest was organized to name the new little brother and was won by an 11-year-old English girl named Venetia Burney, who proposed the name of the Roman god of the underworld, Pluto (Hades, in Greek). Let’s say, the Mictlantecuhtli over there. What a lovely girl.

Suspicious

Pluto was always the odd one out in the family. It is rocky and smaller than the Moon, despite being in the region that we have become accustomed to considering as the domain of the giant planets (Jupiter, Saturn, Uranus and Neptune). Its orbit is very inclined with respect to the plane of the respectable planets, and it also has the audacity to cross the orbit of Neptune, which is why Pluto began to be the most distant planet only in 1999, despite what they taught us in school. .

As if that were not enough, the theory of the formation of the Solar System from the 1950s explained that beyond Neptune there should be a very wide strip full of rocky objects of very varied sizes, even larger than Pluto. This strip is called the Kuiper belt. Since then, astronomers viewed Pluto with suspicion. Would Pluto be a Kuiper Belt object, and therefore one of many similar objects? Should these be included among the planets?