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I read in past that the time that the moon orbits the earth is becoming shorter constantly? (0.3 seconds per 1000 years)

and what is the simple astronomical explanation?

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Check your sources. The claim is unfound and the opposite is true.

Due to tidal friction the moon causes on Earth which in turn slows Earth's rotation, it drifts away from Earth slowly in order to conserve the angular momentum of the combined earth-moon system. A larger separation in turn means that it orbits Earth slower (Kepler's law).

The increase of moon - Earth distance is a well-established thing since lunar laser ranging which started latest with the first landing of an Apollo mission on the moon - by about 3-4 cm/year.

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  • $\begingroup$ According to my notes, I copied this information to my computer from a translated cite of the book "Gates to the Hebrew calendar" p.128 [1]: google.com/… $\endgroup$ – Reckless Glacier Apr 15 at 0:03
  • $\begingroup$ "The accurate length of the month (synodic month) nowadays is 29 days, 12 hours, 44 minutes, 2.8 seconds. As it was said above, this length is going and becoming shorter". Is it not true / nonsense? $\endgroup$ – Reckless Glacier Apr 15 at 0:06
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    $\begingroup$ @UbiquitousStudent Much as with your other, similar question I think the issue here is that you need to be careful of what the definitions are and what they actually imply. The synodic month is the period between phases of the moon, which is different from the sidereal month and varies throughout the course of the year (that's basically the reason why the months don't all have the same number of days) as the variation in the position and distance of the Earth relative to the Sun is relevant. $\endgroup$ – zibadawa timmy Apr 15 at 6:46

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