H Newton's Universal Law of Gravitation
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Isaac Newton

"In the year 1666 he retired again from Cambridge to his mother in Lincolnshire. Whilst he was pensively meandering in a garden it came into his thought that the power of gravity (which brought an apple from a tree to the ground) was not limited to a certain distance from earth, but that this power must extend much further than was usually thought. Why not as high as the Moon said he to himself & if so, that must influence her motion & perhaps retain her in her orbit, whereupon he fell a calculating what would be the effect of that supposition." quotes

Mechanical Universe

The infamous apple thing. . .

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Newton's masterful equation was mostly useless in this form. We did not know Big G - the gravitational constant. Without it, we could not use Newton's law.  There were many physicsists that were re-working the old Ptolemaic system. Galileo was credited with discovering the acceleration due to gravity (little g) at the surface of the earth. Tycho Brahe and Johannes Kepler were also looking toward the heavens to discern the exact nature of the movement of the planets. 
But first, we will need Big G. . .

Henri Cavendish 1731 - 1810

Henri Cavendish did not actually calculate Big G. He actually calculated the mass of the Earth! Galileo, Newton and Cavendish demonstrated that if one observes nature you, too, will discover these remarkable non-mysterious patterns visible to anyone. Newton and his contemporaries brought order where there was chaos. They demonstrated that the Universe was orderly and mechanistic. Newron exhorted, "Tell me all the initial conditions and I will show you the future." Those initial conditions would always prove to be elusive. The scientists of the 16th century were ushering in a new way to experience nature.

Humans were no longer helpless to the elements, the gods and the spirits that once led the way. We took control. Nature was never meant to be a mystery. The patterns were, are and will be visible to whomever wishes to focus. Are these patterns in nature real, objective and immutable? Sure, but who said that a subjective beast can't manipulate real natural laws to travel through space and time? It's always gets cold in the winter, so we wear coats! We don't have wings so let's build a flying machine to defy gravity! We fight microorganisms to defend our delicate cellular ecosystem. . .maybeoneday, we can 'communicate' with the microorganisms to better understand and help both systems!

Galileo Galilei

Since we are still looking, why stop here?
Let's look farther into our own Solar System and the motions of the planets.

So, could we calculate the mass of the Milky Way Galaxy? And, if we assume that our Sun is the average mass of a star could we calculate the number of stars in our Galaxy? With just a few equations derived from observing the simple motions of the planets of our Solar System, we are able to discover the vastness of our own Milky Way Galaxy!

We have yet to answer the question. . .What is Gravity? We know the equation and we can use this equation to launch probes into deep space to land on the Moon or Mars. But, we still have no idea of what Gravity is!

PBS Nova - Elegant Universe

Problems 47, 60

Wilkingson Microwave Anisotropy Probe
Mapping the temperature of the Universe.