Gravity on the surface of the Moon

  • Context: Undergrad 
  • Thread starter Thread starter waterhouse
  • Start date Start date
  • Tags Tags
    Gravity Moon Surface
Click For Summary

Discussion Overview

The discussion centers on the gravitational force on the surface of the Moon, particularly in relation to historical predictions based on Newtonian theory and the actual measurements observed. Participants explore the implications of these measurements on the Moon's density and mass, as well as the methods used to determine these values.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that Newtonian theory predicted the Moon's gravity would be 1/4 that of Earth's, while actual measurements show it to be 1/6, suggesting the Moon is made of less dense material.
  • Another participant asserts that the mass and density of the Moon were known prior to 1969, implying that this knowledge was critical for the success of the Apollo missions.
  • A participant questions how the diameter of the Moon could have been known without prior orbital measurements, suggesting that early orbiters may have encountered unexpected gravitational conditions.
  • Another participant counters that the Moon's diameter and orbital properties can be measured from Earth, indicating that prior knowledge existed before the launch of orbiters.
  • A participant shares a paper discussing various methods of measuring the Moon's mass, indicating a historical perspective on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the historical knowledge of the Moon's mass and density, with some asserting that it was known before 1969 and others questioning how this was determined. The discussion remains unresolved regarding the implications of gravitational measurements and the methods used to derive them.

Contextual Notes

Participants reference the need for precise measurements and the potential for anomalies in gravitational data, but do not resolve the specifics of these claims or the implications for the Moon's composition.

waterhouse
Messages
2
Reaction score
0
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 ?
 
Astronomy news on Phys.org
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
 
Last edited by a moderator:

Similar threads

  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 10 ·
Replies
10
Views
5K
  • · Replies 3 ·
Replies
3
Views
3K
Replies
17
Views
4K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 22 ·
Replies
22
Views
2K
  • · Replies 21 ·
Replies
21
Views
6K