# how did we figure out the weights of planets an such

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#### Cpickens89

##### Guest
when did we learn how to do this ? or better yet who figured it out ?
and is it 100% accurate ?

theres just things im curious about hoping someone would enlighten me never did find much in search sorry if i posted something already asked i might have skipped over seeing it

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#### dragon04

##### Guest
I suppose the short answer is that Isaac Newton "figured it out" based in part on Kepler's Third Law of Planetary Motion. Galileo determined that the acceleration due to the force of gravity of Earth was a constant equal to 9.8 m/sec2 near the surface of the Earth. Later, Henry Cavendish more accurately measured and defined the value for the Gravitational Constant (G).

It is not "100% accurate", but is very very close.

Kepler's Laws
JOhannes Kepler
Galileo
Isaac Newton
Newton's Law of Universal Gravitation
Henry Cavendish
Gravitational Constant

Last but not least, Einstein's General Relativity Theory refined inaccuracies.

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#### drwayne

##### Guest
Through history, observations combined with analysitcal and empirical relationships have allowed astronomers to postulate the existence of other planets that have yet to be discovered.

Through sometimes dodgy analysis, and a large measure of luck, this was how Neptune was discovered.
(This is a fascinating story by the way, I encourage you to read about it)

Wayne

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#### Cpickens89

##### Guest
pretty interesting guy's thanks , i'll definatly read up on this

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#### MeteorWayne

##### Guest
The answer for that has more to do with the moons that orbit the planets. By measuring the orbits of the moons, the mass of the planet can be calculated. The size of the orbit and the period lead directly to a mass through the laws of gravitation.
For the planets without moons, highly accurate masses really had to wait (or weight ) until we had spacecraft pass nearby; during that nearby pass or orbit the motion of the spaceraft leads to highly accurate mass calculations through the sme method.

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#### SpaceTas

##### Guest
If you want to calculate the Mass of Jupiter try the project CLEA http://www3.gettysburg.edu/~marschal/clea/CLEAhome.html the "Revolutions of the Moons of Jupiter"
I found a couple of worksheet google Mass of Jupiter simulation.

Even though the simulations are a bit contrived the process is good.

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