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is there a type of average of the speed of planets travelling in space around the sun, and is that a significant idea?
Are we suggesting radioactive decay is intrinsic to a standard for a universal measurement of time?
assumed the planets moved at the same speed?
even then was it assumed the planets moved at the same speed
For instance, who has measured the weights of planets according to Newton?
Quote from: opportunityFor instance, who has measured the weights of planets according to Newton?Newton's law of gravitation allowed astronomers to weigh (estimate the relative masses) of any astronomical body with an orbiting satellite.- It was easy to find the mass of the Sun - it has orbiting planets- It is easy to measure the mass of Earth and Jupiter, since they have very obvious moons- With better telescopes, it became possible to weigh Mars and Saturn (they also have moons)However, it was only with Cavendish's laboratory experiment in 1798 that Newton's "G" was measured, and this allowed the relative masses of the Sun and planets to be turned into actual masses.So, depending on your viewpoint (theory or practice), the answer could be "Newton" or "Cavendish".See: https://en.wikipedia.org/wiki/Cavendish_experiment
Quote from: opportunity on 17/12/2018 10:12:12even then was it assumed the planets moved at the same speedIn the ancient heliocentric view of the universe it was assumed that we stayed still and the planets etc moved.So, plainly, they didn't move at the same speed as us.Post Copernicus, we accept that all the planets, including the Earth move round the Sun.And that requires them all to have different orbital speeds.When Kepler looked into ithttps://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motionhe deduced the relative speeds of the known planets and, of course, they were all different.And with the measurement of the transit of venus https://en.wikipedia.org/wiki/Transit_of_Venus,_1639He was able to measure the actual speeds so, at no point in history was it "assumed the planets moved at the same speed"... "as us".So why say it was?
The question is how actual planetary speed is calculated.
A question is how Newton calculated the distances of the planets from the sun and masses, and of course thus speed;
Just to get things clear, who knows how Newton did that?