Japanese astronomical terms: “chidousetsu” (地動説) and “tendousetsu” (天動説)

By | May 9, 2019

In this post I want to cover two Japanese scientific terms I have come across: “chidousetsu” and “tendousetsu”. These are generally written in kanji as 地動説 and 天動説, respectively.

Chidosetsu is used to describe the astronomical model whereby the Sun is at the center of the solar system, with planets (including the Earth) revolving around it. More formally, it is called heliocentrism.

Tendousetsu, on the other hand, is the astronomical model whereby the Earth is considered to be the center of the solar system (or the universe), with the sun and other planets resolving around it. This is referred to as geocentrism.

It should be noted that, based on current scientific observations, neither the Earth nor the Sun is the center of the entire universe.

While these terms are relatively straightforward to understand, I think remembering which is which in Japanese is a little confusing. So let’s look at what kanji characters comprise each of these two words:

Chidousetsu:

  • 地 (chi) = ground / Earth
  • 動 (dou) = movement
  • 説 (setsu) = theory / rumor

Here, we can see this word means “the theory that the Earth is moving”, which is consistent with the idea of the Earth not being the center of the solar system or universe (heliocentrism)

Tendousetsu:

  • 天 (ten) = sky / heaven(s) / the universe
  • 動 (dou) = movement
  • 説 (setsu) = theory / rumor

Here, we can see this word means “the theory that the sky/heavens/universe is moving”, which is consistent with the idea of the Earth being the center of the solar system or universe (geocentrism). By the way, the kanji 天 is used in the word for “astronomy”, 天文学 (tenmongaku).

I think the main reason these terms are a little difficult to remember is because they are described in Japanese in terms of what is moving, as opposed to what the center of the movement is, so they can feel backward for English speakers. It may help you to just remember that chidousetsu is the theory that is correct, at least according to current scientific evidence.

If you are interested in learning more science terms in Japanese, please see my vocabulary list of Science terms.

(Note: the time lapse photograph used for the featured image came from Pexels.com)


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