Is it possible know the time according to the moon location? To look at the sky at night and then determine what the time is.

  • $\begingroup$ Sort of. See en.wikipedia.org/wiki/Moondial $\endgroup$
    – PM 2Ring
    Dec 2, 2019 at 7:17
  • $\begingroup$ If you are aware that the moon goes thru phases, and is in a different location in the sky every day, varying from full moon at midnite to new moon at noon, you should see where the difficulty begins. $\endgroup$ Dec 2, 2019 at 15:01
  • $\begingroup$ If you knew your position on Earth and the moon's geocentric right ascension and declination (and adjusted for parallax), you might be able to get an approximation. $\endgroup$
    – user21
    Dec 2, 2019 at 16:10

1 Answer 1


It is not easy.

Knowing the time means (roughly) knowing the position of the sun. If you are in the Northern Hemisphere, then the sun is (roughly) South at midday, East at 6am, West at 6pm and so on.

The moon orbits the Earth, so the angle between the sun and the moon is always changing. It may be possible so reason as "The moon is at first quarter, so the angle between the sun and moon is 90 degrees. I can use the position of the moon to determine the position of the sun (below the horizon) and so estimate the time." There are problems with this, for example when the moon is nearly full, it will move through quite a large angle relative to the sun, with only a very small change in the amount of illumination.

With careful measurements and an almanack, it would be possible to find the local solar time. This wouldn't account for daylight saving time, or civil time that differs from solar time. There are much easier methods: get a sundial during the day and an hourglass for the nighttime. Or a watch.


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