Why is the Moon getting further from Earth ?

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  • Thread starter DaTario
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Hi All,

What is the reason that makes the distance between the Earth and the Moon get larger and larger?

Best wishes,
DaTario
 

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  • #2
phinds
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Hi All,

What is the reason that makes the distance between the Earth and the Moon get larger and larger?

Best wishes,
DaTario
Google is your friend. I just did a search on "moon getting farther from earth"
upload_2018-7-22_10-40-16.png
 

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  • #3
Bandersnatch
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The reason is tides.

The tidal bulge risen on Earth by the Moon is offset from the line connecting the two centres of masses by Earth's rotation due to limited response time of Earth surface (and oceans) - cf. Love numbers.
The offset bulge is acted upon by gravity of the Moon, providing torque to Earth (causing slowing of rotation period) and to Moon (raising it in its orbit).

Googling for 'tidal acceleration' and selecting pictures will let you see some free body diagrams of the system.
 
  • #4
Buzz Bloom
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Hi DaTario:

The simple answer is that the lunar tides create a bulge of water which acts by friction to (1) slow the Earth's rotation, and (2) gravitationally to speed up the moon's revolving around the Earth. The details of the friction and the gravitational effects are too complicated for me to try to describe.

Hope this helps.

Regards,
Buzz
 
  • #5
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There are also Earth tides, less obvious but significant if you've an LHC or radio-telescope array. Or are monitoring a volcano via GPS...
https://en.wikipedia.org/wiki/Earth_tide
IIRC, although the total is constrained, there is not yet agreement on how much Earth-tide energy is dissipated where within our world.

OT: Based on a small sample, you must wonder how much the Moon's tidal stirring influences our lively plate tectonics...
 
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I like to think of it like the offset bulge in the tides is pulling the moon like a horse pulling a cart. Pulling it would make it go faster but the energy goes into taking it higher in orbit around the Earth.
If the Moon were moving against the rotation of the Earth, I gather the Moon would be lowering in orbit, and reach the Roach Limit, and break up.
 

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