Mass of the Sun
To measure the mass of the Sun would seem to be hard, but actually
it is easy.
Newton's laws of motion together with his law of gravity give a relation
(For our purposes, assume the orbits are circles. Also assume that the
mass of a planet is tiny compared to the mass of the Sun.)
- the period P of a planet's orbit.
- the distance a from the planet to the Sun.
- a constant G measured in laboratory experiments.
- the mass M of the Sun.
The relation is
Using this relation with P and a for the Earth
gives the mass of the Sun.
M ~ 2 x 1030 kg.
We will use this relation later on to get the masses of other stars.
It can also be used to get the masses of galaxies!
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA