Often—in fiction—a character might say, "it's been seven moons since the death of my aunt Wilma." What exactly is a "moon"? How many moons are in an hour, in a day, in a week?

I'm scientifically interested in "moons" as a unit of time. Obviously, this varies based on what planet you are on, and of course, which moon you are referring to, but Earth has only one moon, so for the purpose of this question, Earth is the context.

  • I could be wrong, but I believe they say "moon" as another word for "night" in that context.
    – Arvex
    May 2 '17 at 1:52
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    yeah, I considered this also, but I thought it had something to do with the actual lunar cycle potentially. not sure.
    – John Watmuff
    May 2 '17 at 2:00
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    @Arvex Sorry it's not so. JohnWatmuff is right. It is to do with the lunar cycle.
    – a4android
    May 2 '17 at 2:02
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    Moon, in the context you ask, is either the Full Moon to Full Moon OR New Moon to New Moon. There is nothing that forces it to be this way but before there was the Calendar we use today, blocks of days was based on a full Lunar Cycle. It takes our Moon about 29.5 days to complete one cycle of phases (from new Moon to new Moon)
    – Enigma Maitreya
    May 2 '17 at 4:49
  • @JDługosz Conceptually, yes. But any questions which can be immediately answered by looking up the word in a dictionary or other reference work are inappropriate and off-topic on EL&U. Please do not migrate such questions. In this case, if OP had looked up moon in any dictionary, looking for a glosses relevant to durations, he wouldn't have had to ask the question in the first place.
    – Dan Bron
    May 2 '17 at 11:34

A moon is a unit of time corresponding to a month. Usually this means one lunar month when the Moon goes through its cycle of phases. There are thirteen lunar months in a year.

This means Aunt Wilma died seven months ago. There are remarkably few moons in a hour or in a day. The societies that measured time in moons lacked the technological contrivances make clocks. It can be described as an imprecise measure of time. But didn't matter because they didn't measure with precision we do. That sort of precision only came in with the railways.

The only scientific sense that moons are measures of time is the period of the lunar moon.

  • Indeed, in English there's only a minor difference in spelling/pronounciation: moon <-> month.
    – jamesqf
    May 2 '17 at 4:30
  • @jamesqf We called our Moon Luna, as often happens in science-fiction, we'd be calling months "loons".
    – a4android
    May 2 '17 at 4:45
  • I would note that China, Judaism, and Islam at least still have important lunar calenders.
    – user219159
    May 2 '17 at 15:09
  • @notstoreboughtdirt The Chinese calendar is lunisolar, not lunar.
    – choster
    May 3 '17 at 15:11

When you look up in the sky at the moon you'll see either nothing or one of these:

enter image description here

The biggest misconception is that the earth casts a shadow on the moon. It does not. Phases are caused by the illumination of the moon by the sun.

If it's been seven moons, it's been AT LEAST seven months since Auntie died. This can either be counted from the phase of the moon when Auntie died--it was at ANY specific phase and the character has seen that phase 7 times (like 1/2 or new), OR she died during any phase and the character has seen a full moon 7 times since then. As a4android says, in ancient times, it wasn't a precise measure, but a round about.

Get to know our cycles, how they work and why, so that when you are building another, you can figure it from there---just because planet has a single moon will not mean it works exactly like ours, with the same unit of time measurement.

  • 1
    Nice answer. Good point about the Earth not casting its shadow on the Moon to cause the phases. Great illustration about phases of the Moon. Plus one from me.
    – a4android
    May 2 '17 at 4:43
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    Ah, but the earth does cast its shadow on the moon (on rare occasions). This is what is called a lunar eclipse.
    – Hot Licks
    May 2 '17 at 11:29

As mentioned on the world-building stack exchange, "moon" in this context refers to a unit of time measuring one month, mostly in antiquated, archaic, or fantasy-writing settings. It derives, naturally, from the lunar cycle. The moon revolves around Earth twelve times per year, and in ancient history was an important tool for measuring time.

The word "month" actually has an etymological relationship with moon:

diagram of month etymology

Also see moon as described on Etymonline.com:

Old English mona, from Proto-Germanic *menon- (source also of Old Saxon and Old High German mano, Old Frisian mona, Old Norse mani, Danish maane, Dutch maan, German Mond, Gothic mena "moon"), from PIE *me(n)ses- "moon, month" (source also of Sanskrit masah "moon, month;" Avestan ma, Persian mah, Armenian mis "month;" Greek mene "moon," men "month;" Latin mensis "month;" Old Church Slavonic meseci, Lithuanian menesis "moon, month;" Old Irish mi, Welsh mis, Breton miz "month"), probably from root *me- "to measure," in reference to the moon's phases as the measure of time.


A moon cycle is 28 days (the time from one full moon to the next), so a week is 1/4 of a moon cycle. However, typically the people that measured time in full moons would not talk about quarters of the moon cycle; they measure smaller periods like a week in days or nights. Up to about a "fortnight" which was fourteen days which is half a moon cycle. They might use that period, 1/2.

The ideas of "hours" and "minutes" are pretty recent inventions only a few centuries old (maybe five centuries?) In a primarily rural and non-industrial world, examine the language we used before: "morning" "afternoon" and "night" were close enough, a "moment", "quickly", "hurry", and other timely notions are very general and can mean anything from seconds to hours depending on the context of the task: "quick" milking of goats is different than "come quick."

So things like an aunt dying a week or days ago could be described as "just happened", and not specified precisely at all: To a speaker not accustomed to thinking of life events as sharply delineated in time; if they are still in the emotional grips of such a death, in their mind the death may still be an event in progress. That may be alien to those of us raised on the clock; but unclocked people (not raised on a clock) can see their lives as a sequence of (sometimes overlapping) events.

For example; "I got married" followed by "I got pregnant". How much time passed between those events may not be known for an unclocked person, because nothing of similarly memorable import happened to her in-between those events.

Had we said it, it is like her asking us "how many miles did you walk in-between those events?" We don't know, most of us don't really keep track of how many miles we walk, and it would be hard to estimate.

So our unclocked mother may be able to tell us many other events she recalls that happened in-between without an exact handle on days, weeks or months. And without understanding why we think that makes any difference.

  • 1
    Welcome to ELU. Please note that this is a Question and Answer site, for specific answers to specific questions, not a discussion forum. Although what you've written in the "Answer" box is interesting, it doesn't actually answer the question "How many moons are in a week?". If you don't edit this in, your post is likely to be deleted as "not an answer".
    – AndyT
    May 3 '17 at 13:38

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