Our moon: Natural or Artificial?

Odysseus
Odysseus
Joined: 17 Dec 05
Posts: 372
Credit: 19,464,887
RAC: 2,442

RE: RE: 2. You always

Message 21097 in response to message 21075

Quote:
Quote:

2. You always get to see the same half of the moon because it is rotating at exactly the same rate it is moving around the earth: 29.5 earth days

This is actually not a coincidence at all, but rather a stable equilibrium resulting from the tidal forces exerted by Earth on the Moon. [...] Mercury is nearly close enough to the Sun to be tidally locked itself.

In fact Mercury is tidally locked to the Sun, in a way: its orbital and rotational periods are in a 3:2 resonance.

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,528
Credit: 281,678,514
RAC: 42,810

RE: In fact Mercury is

Message 21098 in response to message 21097

Quote:
In fact Mercury is tidally locked to the Sun, in a way: its orbital and rotational periods are in a 3:2 resonance.


In fact there are quite a lot of resonances in the Solar system, a book called "Newton's Clock - Chaos In The Solar System" by Ivars Peterson describes this beautifully. For example, if an asteroid turns up too near the orbit of Jupiter when Jupiter is too nearby, then this behaviour probably does not have a long term career - it will collide or get flicked off into another orbit with different timing. The chaos refers to quasi/nearly periodic behaviour and trying to predict the long term on that. It is certainly not completely understood. He also describes purpose built computers called 'orreries' which crank through the numbers to track behaviour - the trouble is a very small variation at some number of digits after the decimal point does not remain small. The errors get bigger without bound and with ultimately unpredictable results for some level of precision after a certain computation time.

I have made this letter longer than usual because I lack the time to make it shorter ...

... and my other CPU is a Ryzen 5950X :-) Blaise Pascal

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.