Talk:Lunar day

message: Want to help write or improve articles about Time? Join WikiProject Time or visit the Time Portal for a list of articles that need improving.
—Yamara ✉ 20:34, 17 March 2008 (UTC)
thread_title:  [[Wikipedia:WikiProject_Time/Assessment|WikiProject Time assessment rating]] comment 

message: The article currently states, regarding the Lunar day: "Equivalently, it is the time it takes the Moon to make one complete orbit around the Earth and come back to the same phase. It is marked from a New Moon to the next New Moon." Is this correct? It seems to me that the point one the Moon's surface directly opposite the Earth varies due to lunar libration, so the time of the new Moon varies as well, but this should not affect when an observer on the Moon observes the Sun at zenith, say.--agr 17:03, 1 July 2007 (UTC)
replies: text: The period the article describes corresponds to the Synodic_month#Synodic_month, the "month of the phases". I agree that due to libration the position of the Earth in the lunar sky will vary, but wouldn't the same oscillation also affect the Sun's position in the lunar sky?  Phases are based on the illuminated fraction, seen from the Earth, but not on which exact lunar hemisphere it is a fraction of.  I hope this helps. Hertz1888 03:57, 2 July 2007 (UTC)
replies: text: I was looking at this again and I think there is still an issue here.  Someone on the Moon would want to know the interval between successive sunrises.  That is not necessarily the same as the time between successive new moons, the synodic month, because of libration, and it is also not the same as the sidereal month because the moon moves relative to the sun during the month.  It might well average out to the synodic month, but that doesn't make the two concepts equivalent. The amount and timing of variation from mont to month may well differ.--agr (talk) 20:59, 30 March 2012 (UTC)
thread_title: Equivalence?

message: This is horribly confusing to anyone trying to work out the actual sidereal day on the moon.
Let's say I wanted to make a lunar colony. I need to open the blinds to vent heat every 14.781 days, right? But if this is based on an Earth day, then my calculations will be off by 4 minutes every Earth day, which means it won't take long for my automated system to irradiate all the residents and lose the colony.
Of course, I am basing this (dubious) calculation on the following (dubious) statement:
"As a result, daylight at a given point on the Moon would last approximately two weeks from beginning to end, followed by approximately two weeks of night."
Is that based on the synodic day (assuming that a tidally locked celestial body's day is affected by the object it orbits; "takes longer to return to the same phase", i.e., the same division of light and darkness on the same longitudinal axis), or the sidereal day?
If I take the figure given for the sidereal day as fact, "relative to the fixed stars on the celestial sphere, the Moon takes 27 Earth days, 7 hours, 43 minutes, and 12 seconds to complete one orbit" –I again have the same problem. Is that 27 24:00:00 days? Or are those 27 days each 23.9345 hours long?
I am sure I'm not the only one confused by this, but if anyone could shed some daylight on this (ahem) I'd appreciate it.  — Preceding unsigned comment added by Chaim1221 (talk • contribs) 22:17, 20 July 2019 (UTC)
thread_title:  29 days, 12 hours, 44 minutes, 3 seconds