Why Does the Moon & Earth Have Different Relationships with the Sun?

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Discussion Overview

The discussion centers on the differing tidal relationships between the Moon and Earth compared to the Earth and Sun, specifically addressing why the Moon is tidally locked to the Earth while the Earth is not tidally locked to the Sun. The scope includes theoretical explanations and mechanics of tidal locking.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that the Moon keeps the same face toward the Earth due to tidal locking, which is influenced by the proximity and size differences between the Moon and Earth compared to the Earth and Sun.
  • Another participant explains that tidal forces are proportional to 1/R3, suggesting that the closer distance and smaller size of the Moon contribute to its rapid tidal locking.
  • A participant expresses interest in further mechanics of tidal locking and seeks additional resources.
  • It is mentioned that while no planets are tidally locked, most close-in moons are, with a possible exception noted (Hyperion).
  • One participant questions whether it is correct to assume that any orbiting body will eventually become tidally locked given sufficient time.

Areas of Agreement / Disagreement

Participants present various viewpoints on tidal locking, with some agreeing on the mechanics involved while others raise questions about the generalization of tidal locking to all orbiting bodies. The discussion remains unresolved regarding the assumption that all orbiting bodies will become tidally locked over time.

Contextual Notes

Limitations include the dependence on specific conditions such as distance and size, and the discussion does not resolve the complexities of tidal locking mechanics or the assumptions behind the question of whether all orbiting bodies will eventually become tidally locked.

Who May Find This Useful

Readers interested in astrophysics, celestial mechanics, and the dynamics of orbital relationships may find this discussion relevant.

Martin Rattigan
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Why does the Moon keep the same face toward the Earth but the Earth not keep the same face toward the Sun?
 
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It's tidal locking. Tidal forces are proportional to 1/R3.

The Moon is much closer to the Earth than the Earth is to the Sun. The Moon is also much smaller than the Earth and much lumpier than the Earth. All of these things combine to make the tidal lock time for the Moon an extremely short time (astronomical time frame) while the tidal lock time for the Earth is very, very long.
 
I thought that was probably it. Do you know of anywhere that goes thro' the mechanics of that?

OK - I found something thro' Google - Thanks.
 
Last edited:
Indeed, no planets are tidally locked, and almost all close-in moons are. (I think there is one exception - Hyperion) R3 is the reason.
 
I've wondered about this, for a while: Is it correct to assume that, given enough time, any orbiting body will become tidally locked?
 

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