Is there a way for the moon to be seen at every point during the daytime? In my world it is day all the time so they have a rough concept of months, years and days. To solve this they could have moons that can be seen during the day. Is it possible?

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    $\begingroup$ Just out of curiosity, have you looked outside today? $\endgroup$ – anongoodnurse Aug 7 '15 at 21:46
  • $\begingroup$ No I mean all the time, all day, every day $\endgroup$ – TrEs-2b Aug 7 '15 at 21:47
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    $\begingroup$ I don't understand your question. Do you want to know if it is possible for a natural satellite to be tidally locked to its primary, and vice versa, so that hemisphere A of the satellite will always face hemisphere A of the primary? If so, look into Pluto and Charon, and bear in mind that it will only be possible for two bodies of comparable size. If that wasn't your question, please elaborate and specify it better. $\endgroup$ – fantasia Aug 8 '15 at 0:15

No, I don't think there is a way for the moon to be visible all day every day and still have phases

I'm going to assume Earth-like conditions.

For the moon to be visible all day every day, it would have to have no orbit at all around the "earth" - that is, it would have to be stationary in space - and it would have to be best if on the opposite side of the earth from the sun.

enter image description here).

You can pick a 1st quarter to 3rd quarter moon. If the moon was still, and your planet orbited, the entire planet would see the moon all day. But it would never have a phase change because it is stationary. (At night, they would not see it... which brings us to the next question...)

There is no planet that we know of that has a stationary moon, because of the way moons are formed or captured.

Better to have multiple moons. But how your planet exists in all daylight is the other question. It would get mighty hot.

  • $\begingroup$ It has a day that last longer than its year. one day there lasts for 9 of their years $\endgroup$ – TrEs-2b Aug 7 '15 at 22:19
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    $\begingroup$ That makes very little sense. The planet would be rotating tonce for every nine times around their sun? Then part of the planet would be dark as well. $\endgroup$ – anongoodnurse Aug 7 '15 at 22:22
  • $\begingroup$ yes that's correct but what about makes little sense $\endgroup$ – TrEs-2b Aug 7 '15 at 22:24
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    $\begingroup$ Alien Planets With No Spin May Be Too Harsh for Life. $\endgroup$ – anongoodnurse Aug 7 '15 at 22:28
  • $\begingroup$ Other people disagree with you here; worldbuilding.stackexchange.com/questions/20799/… also it says "may be" not is or are And finally this planet isn't tidally locked it just has a slow rotational spin but still a rotational spin $\endgroup$ – TrEs-2b Aug 7 '15 at 22:30

I haven't double-checked this on paper with math and graphs, but for a single moon, my knee-jerk reaction is that the moon would need to orbit the planet with the same orbital period that the planet orbits the star: 1 month = 1 year

EDIT: come to think of it, this would make the moon useless for time-keeping. Multiple moons would be the way to go: sometimes none of them are visible, sometimes all of them, sometimes some but not others...


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