Gravity on the surface of the Moon

AI Thread Summary
The discussion centers on the discrepancy between the predicted gravity on the Moon's surface, which was thought to be 1/4 that of Earth's based on Newtonian theory, and the actual measurement of 1/6. It clarifies that the mass and density of the Moon were known prior to the Apollo missions in 1969, allowing for successful navigation. Participants debate how the Moon's diameter and mass were determined, emphasizing that measurements could be made from Earth without needing orbiters. There is a mention of early landers not being designed for landing rather than issues with unexpected gravity. The conversation highlights various methods used to measure the Moon's mass throughout history.
waterhouse
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I recently heard someone claim that not too very long ago Newtonian theory based on the size of the moon predicted gravity on the moons surface would be 1/4 that of earth. The actual observation was that it is 1/6 that of earth. The conclusion supposedly is the moon is made of material less dense than that of earth.

can someone tell me if in fact it was a surprise back in 1969 , and if we now know whether the needed mass of the moon to make the observation agree with the theory is supporeted by the material , dust layer depth etc ?
 
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No, we knew the mass and density of the Moon back in 1969, and way back before then. Otherwise the Apollo astronauts would never have got home.

Garth
 
Thanlks garth


Well , I agree inferences could have been made etc.

But , the exerted gravity is a function of both the mass and the distance from the surface of the moon to its center of mass.

How could we have known the diameter until an orbiter went around it

Isnt it true that some of the first orbiters crashed early becasue the actual gravity was higher than expected ( or anomylous on the far side not sure which)

It seems that the only way we derive the mass is by knowing the distance and plugging it into Newtons equation.

Or do you know of another way to measure the mass?
 
waterhouse said:
How could we have known the diameter until an orbiter went around it
The diameter of the moon and the properties of its orbit can be directly measured from earth. It is close enough for that.
Isnt it true that some of the first orbiters crashed early becasue the actual gravity was higher than expected ( or anomylous on the far side not sure which)
No, the early "landers" were quite simply not designed with the ability to land.
It seems that the only way we derive the mass is by knowing the distance and plugging it into Newtons equation.
 
Here's a nice paper on many different methods of measuring the moon's mass, stretching from the time of Isaac Newton to the present day. It's an interesting read!

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?db_key=AST&bibcode=2002Obs...122...61H&letter=.&classic=YES&defaultprint=YES&whole_paper=YES&page=61&epage=61&send=Send+PDF&filetype=.pdf

- Warren
 
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