Universal Gravitation

Universal Gravitation

Copernicus had another great champion in Johannes Kepler, a German astronomer and mathematical genius whose study of the observations of Tycho Brahe led him to discover that the planets move in elliptical orbits. Kepler determined the nature of the motions in these orbits and in so doing dispensed completely with the Greek concept of uniform motion in a circle. The elaborate system of circles used by Ptolemy and Copernicus to account for the observed motions of the planets were reduced to six ellipses, and the solar system acquired its modern form.

The next major step was made between 1665 and 1687 by Isaac Newton who, from observation of a falling apple, deduced that the earth exerted a pull of “force of gravitation” on the moon. Under the action of this force the moon would simply fall to the earth but was prevented from doing so by its speed in its orbit. In a similar way, each planet was under the gravitational control of the sun. Newton`s calculations showed that since each planet moves in an eclipse, the force of gravitation varied directly as the product of the masses of the sun and planet, and decreased as the square of the distance between them increased.

Newton’s Telescope. Replica of Newton’s reflecting Telescope

Armed with this law Newton was able to put the theory of the tides, the precision of the equinoxes, the complex motions of the moon, and numerous other events on a sound dynamical basis. In effect he demonstrated that the principle and relationships found in terrestrial mechanics could be applied in celestial places. To him the physical universe was a great machine whose parts were controlled by the forces acting on them, but whose construction and working demonstrated the design and purpose of God.

Newton also established optics as a science. He invented and made a new type of telescope, the reflecting telescope, and discovered that the sunlight is composed of the different rainbow colours of the spectrum. Through the development of the first, astronomers were able to probe further into the immensity of space than ever before. Through the second they learned how to analyze starlight and discover the physical natures of the stars – their surface temperatures, chemical composition, sizes, masses and even how they shine.

Sir Isaac Newton (1642-1726)