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View Full Version : What controls long-term variations in the size of the lunar orbit?



Robert S. Fritzius
2009-Feb-14, 07:43 PM
I did some Googling on variations in the size of the lunar orbit and so far have found three theoretical studies that indicate that the lunar orbit should currently be increasing in size with time. Didn't find any studies that suggest otherwise. Didn't find any details as to the "why" of the process.

Would welcome an explanation about whatever physical process it is that would control long-term variations in the lunar orbit size.

IsaacKuo
2009-Feb-14, 09:31 PM
Tidal effects with the Earth. Earth rotates once per day, which is faster than the rate at which the Moon revolves around the Earth (once per month). Tidal forces from the Moon, cause a torque which slows down Earth's rotation; there's a corresponding torque in the other direction on the Moon. This torque has the effect of gradually raising the Moon's orbit; counterintuitively the Moon's orbital speed as well as the Moon's angular rate of revolving around the Earth actually slows down.

Robert S. Fritzius
2009-Feb-15, 01:38 AM
Tidal effects with the Earth. Earth rotates once per day, which is faster than the rate at which the Moon revolves around the Earth (once per month). Tidal forces from the Moon, cause a torque which slows down Earth's rotation; there's a corresponding torque in the other direction on the Moon. This torque has the effect of gradually raising the Moon's orbit; counterintuitively the Moon's orbital speed as well as the Moon's angular rate of revolving around the Earth actually slows down.

Thanks Isaak!

I found a complementary explanation under the title "Earth Moon Interaction"

http://burro.astr.cwru.edu/Academics/Astr221/SolarSys/earthmoon.html

slang
2009-Feb-15, 01:45 AM
I guess ascending pharaos impacting the moon isn't a very good answer, is it? :D

hhEb09'1
2009-Feb-15, 02:34 AM
I guess ascending pharaos impacting the moon isn't a very good answer, is it? :DWe'd have to move it to ATM (Ascending Theocratic Monarchs)

Jeff Root
2009-Feb-15, 02:59 PM
But the increase in the Moon's period is a secular change!

(The word "secular" means "long-term"; "over a long time period".)

-- Jeff, in Minneapolis

Robert S. Fritzius
2009-Feb-16, 04:55 AM
I guess ascending pharaohs impacting the moon isn't a very good answer, is it? :D

Nope. He missed it all together. :hand:

Robert S. Fritzius
2009-Feb-16, 04:59 AM
But the increase in the Moon's period is a secular change!

(The word "secular" means "long-term"; "over a long time period".)

-- Jeff, in Minneapolis

That, sir, is good! :)