Judging by Lewis and Short (and other sources), planeta means a wandering star and was borrowed from Greek. Apparently the word is post-classical, and the classical expression is stellae errantes/erraticae/errones, used (almost?) exclusively in plural.

When the word planeta enters Latin literature, is it defined? Is it ever explicitly linked to the classical version mentioned in L&S? I would like to know what the word meant in Latin. (I prefer classical Latin, but if the word is younger than that, I won't require it.) If the meaning evolved over time, an account of this evolution would be great.

My best guess is that it means any bright spots in the sky that move. That may or may not include the Sun and the Moon, but it most certainly does not include other actual stars than our own. I would assume the definition should be extended to objects visible with a telescope but too dim for the naked eye, although such conclusions can be hard to extrapolate from extant literature. Perhaps comets are planetae too. One of the most famous test cases is Pluto, whose planetship has been revoked. Would Pluto be a planeta using the early meaning of the word?

I think that in modern Latin it is wisest to use the word planeta to mean precisely the same thing as "planet" to avoid confusions. This definition is almost certainly different from the earlier meaning.

  • If you would prefer a more formal title for this question, please let me know in a comment or in the chat.
    – Joonas Ilmavirta
    Commented Jul 4, 2017 at 18:40
  • 2
    FWIW, septem planetae is a common cultural reference, from which the names of week days in some languages come. It includes the Moon and the Sun, besides the 5 -non-Earth- planets known from antiquity. The seven-day week with planets in their names seems to be post-classical.
    – Rafael
    Commented Jul 4, 2017 at 19:33
  • For anyone willing to do more research, see also this: the concept seems to be classical, although I'm hesitant to accept that the word was specifically planeta in Classical Latin. Looking for septem planetae in Perseus gives results from the IV century onwards.
    – Rafael
    Commented Jul 4, 2017 at 19:55
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    @Rafael. Pace "Wikipedia", the "planetary" week is alluded to by Tibullus in the first century BC, so it is classical, not post-classical.
    – fdb
    Commented Jul 8, 2017 at 9:11
  • Are you interested in any possible differences between the Latin and Greek ideas? "Erro" is just a literal Latin translation of "πλανάω," so I don't think an educated Roman would have had any trouble distinguishing a transliteration from the "native" Latin term.
    – brianpck
    Commented Mar 15 at 16:49

1 Answer 1


In the context of ancient astronomical theory a “planet” or “wandering star” is any heavenly body that changes its apparent location in relation to the other stars, as opposed to “fixed stars”, which are always at the same visible distance from one another. It is not that the “fixed” stars do not move; they do move, but always in unison with the other fixed stars. The ancients recognised seven planets: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn. They did not know Pluto, but if they did they would have accepted it as a planet, since it fulfils the same conditions.

  • 2
    I'm pretty sure your final comment about comets and meteors is incorrect: the ancients knew about them but didn't think of them as planets (at least universally). The very name "meteor" comes from the fact that it was viewed as an atmospheric (ie sublunar) phenomenon, not an astronomical one.
    – brianpck
    Commented Mar 17 at 0:47
  • @brianpck You are right. I have cut the bit about comets and meteors.
    – fdb
    Commented Mar 17 at 9:46

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