Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Moon's Weight
Name:   Michael
Status:   educator
Age:   40s
Location: N/A
Country: N/A
Date: 1999 - 2000

I have read the weight of the moon is about 81 billion tons. How is this calculated?

Sir Isaac Newton calculated that the gravitational force between objects (say planets, or anything else) is proportional to the square of the masses, and inversely proportional to the square of the distance between them. Cavendish measured the constant of proportionality. It is known as follows:

f = GMm/r^2

By using a body's mass, knowing the force (mg) and the radius of the earth, the mass of the earth can be calculated.

Now, knowing the mass of the earth, and the orbital radius of the moon, and the acceleration of the moon about the earth, the mass of the moon can be found.

--Nathan A. Unterman

Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory