How to Treat Geological and Astronomical Terms

By Mark Nichol

Determining whether to refer to geological and astronomical terms with initial uppercase or lowercase letters can be a challenge, because various publications and publishers differ on capitalization style. The following guidelines, however, appear to predominate:

Names of geological time spans are capitalized, but the terms for the magnitude of duration (eons, eras, periods, epochs, and stages, in descending order of length), are not; in scientific and nonscientific prose alike, these terms can be omitted:

“The Mesozoic is also known as the Age of Dinosaurs.”

“Mrs. Wattle has been teaching Freshman Composition since the Mesozoic.”

Whether modifying terms such as early, middle, and late are capitalized depends on whether they are themselves modified:

“Tyrannosaurus rex lived during the Late Cretaceous.”

“The Deccan Traps erupted in the very late Cretaceous.”

“Ice age” is considered a generic term because multiple such events have occurred.

In astronomy, general terms in proper names of celestial bodies are generally capitalized (“Orion’s Belt,” “Barnard’s Star,” “Comet Halley”). Note, however, that comet is lowercased in lay references to “Halley’s comet.”

In nontechnical contexts, sun and moon are often lowercased:

“She shielded her eyes from the bright light of the sun.”

“Beware when the moon is full.”

In works about astronomy, or those in which other celestial bodies are referenced, uppercase them:

“The Sun is merely one of countless stars.”

“The Moon orbits our planet roughly every twenty-eight days.”

The same rule applies to the name of our planet. In idioms such as “where on earth,” “down to earth,” and “move heaven and earth,” the name requires no emphasis, and references to our world from a surface perspective and to its soil are likewise lowercased:

“I traveled to the four corners of the earth to find it.”

“The earth here is rich and loamy.”

But the word as the name of the planet should be emphasized like any other:

“The first four planets, Mercury, Venus, Earth, and Mars, consisting mostly of rock and metals, are called the terrestrial planets.” (Note that Earth, in such contexts, need not be, and rarely is, preceded by the.)

General terms like “solar system,” galaxy, and universe are usually not capitalized; some publications and books uppercase them (especially in references to our own solar system and the Milky Way galaxy). Names of celestial phenomena and objects such as the aurora borealis and the rings orbiting Jupiter and Saturn are lowercased.

Remember, too, when discussing the planets orbiting the Sun, that Pluto was in 2006 demoted to a dwarf planet — one of four in the solar system’s distant Kuiper belt (a fifth dwarf planet lies in the asteroid belt, between the orbits of Mars and Jupiter), and may not even be the largest one. (The scientific jury is still out on whether the similarly sized Eris is larger).

And why is belt capitalized in “Orion’s Belt” and not in “the Kuiper belt”? In the former term, it’s a reference to part of the personification of the Orion constellation, but in the latter, it’s merely a description, just as in “the asteroid belt.”

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9 Responses to “How to Treat Geological and Astronomical Terms”

  • Peter

    In nontechnical contexts, sun and moon are often lowercased: […]. In works about astronomy, or those in which other celestial bodies are referenced, uppercase them

    That strikes me as silly. “Sun” and “moon” (unlike, say, “Earth” or “Mars”) are not names, so should not be capitalized, whatever the IAU says (but if you’re going to follow IAU recommendations, “Solar System” should be capitalized, too). Science fiction writers, when calling them by name, generally use the Latinate name “Sol” and “Luna” for the sun and moon (which are thus capitalized, being actual names…)

  • Cecily

    Same question as on yesterday’s post:

    I’m intrigued at your repeated use of “lowercased” and variants as verbs, rather than “lowercase” and “uppercase” as adjectives. Is that common in AmE?

    Also, “uppercase” surely means all capitals, whereas you seem to be referring to initial capitals.

  • Mark Nichol

    Cecily:

    Yes, though I think few people other than editors and teachers routinely use uppercase and lowercase at all, they commonly employ those words as verbs in the United States.

    Capitalized is technically imprecise for referring to initial capitalization, but even among editors, it seems safe to use the word alone without risk of confusion.

  • Peter

    though I think few people other than editors and teachers routinely use uppercase and lowercase at all

    And programmers…though I’d use “upcase” and “downcase” as the verbs.

  • Terra Anderson

    My mother-in-law says Orion is not capitalized but my husband and I disagree… Help!

  • Mark Nichol

    Terra:

    You should know by now that the mother-in-law, like the customer, is always right.

    In this case, it’s not just a diplomatic courtesy — all constellation names are proper names based on mythological characters or creatures and are thus capitalized.

  • Dale A. Wood

    To Mark Nichol:
    In your last comment (the sixth one, above), you said the exact opposite of what you should have said or meant to say:
    “My mother-in-law says Orion is not capitalized”.
    “You should know by now that the mother-in-law, like the customer, is always right. In this case, it’s not just a diplomatic courtesy…”

    No – the mother-in-law is wrong. “Orion” is a capitalized word, just as are then names of all 66 of the constellations because they are PROPER NOUNS – and no further explanation is needed.

    You said: “all constellation names are proper names based on mythological characters or creatures”, and this is not true.
    There are constellations that are named for inanimate objects in both the northern and southern hemispheres.

    Up north, we have Libra, the scales, Eridanus, the river, and Corna Borealis – the Northern Crown.
    The southern sky abounds with inanimate constellations that were named for the Microscope, the Telescope, the Southern Cross, and a former one that was named “the Ship” in English. This large constellation was broken into three pieces later on: the Sails, the Poop Deck, and the Keel – where the later is “Carina” in Latin. Also, the Keel refers not just to the very bottom of the ship, but to its entire hull.

  • Susan

    Proper nouns should be with a capital letter, e.g. Saturn, Mars, Earth, Moon, Sun if they are referred to as NAMES, otherwise not. The name of our planet is the Earth, and the moon that orbits us is the Moon, a proper noun/name and the sun WE orbit is the Sun (proper noun/name). There are other moons that orbit other planets and these are meant generally. In scientific texts it would be perfectly logical for this reason, to call our moon “the Moon” and our sun “the Sun”, in just the same way as we would call our planet the Earth.

  • Adrian

    In volcanology we use terms to identify different eruption styles, e.g. (hawaiian style, identified as continuous lava fountaining and named after activity seen on Hawaii; strombolian style, identified as intermittent eruption bursts as seen on the island of Stromboli, plinian style, identified as sustained volcanic ash plumes first described by Pliny the Younger at Vesuvius, AD 79….etc). The literature varies on capitalisation, e.g. plinian versus Plinian. I don’t see eruption styles as proper nouns, so prefer not to capitalise, but then again one could apply the same argument for why we capitalise geological time spans (e.g. Mesozoic). What is your view? Or is this a case of personal preference?

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