[extropy-chat] Astronomical question

Ian Goddard iamgoddard at yahoo.com
Mon Feb 28 05:28:14 UTC 2005


--- Mike Lorrey <mlorrey at yahoo.com> wrote:

> It is a well known phenomenon that the moon is
> draining angular momentum from the earth, thus 
> slowing earth's rotation and causing the moon to 
> orbit at a greater distance from earth.
> 
> I just started wondering if anyone has figured out
> how far away the moon has to get to escape earth 
> orbit, how far into the future that will happen, 
> and how much earth's day will be slowed by the time 
> that happens.....


 That process wont continue indefinitely. What's
happening is that the earth/moon system is slowly
"gravitating" toward synchronous rotation, or tidal
lock. 

 The moon is already tidally locked on the earth (and
thus only one side of the moon faces the earth). The
earth's rotation is slowing due to the moon's
influence only to the point where it too will be
tidally locked to the moon (at which point an observer
on the moon would see only one side of the earth). The
moon's moving away is part of this process and is due
to conservation of the momentum in the earth/moon
system such that as the earth losses momentum the moon
gains it in taking a wider orbit. 

 Once the earth/moon system has reached synchronous
rotation, or orbital stability, it's my understanding
that the earth/moon-system-induced changes in question
(earth slowing & moon recession) will be stabilized.
That would probably be millions of years from now.



http://iangoddard.net/journal.htm

David Hume on induction: "When we have lived any time,
and have been accustomed to the uniformity of nature,
we acquire a general habit, by which we always
transfer the known to the unknown, and conceive the
latter to resemble the former. By means of this
general habitual principle, we regard even one
experiment as the foundation of [empirical] reasoning,
and expect a similar event with some degree of certainty."

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