Keplers three Laws of Planetary Motion

Kepler’s three laws deal with how the planets orbit the sun. Johannes Kepler (1571-1630) in 1599, as a former assistant to Danish Astronomer, Tycho Brahe (1546-1601), was a note taker and observer of the stars, galaxies, and heavenly matters, worked hard to understand how the rotations of the planets took place. He was not in agreement with Copernicus, (1473-1543) who stated the five planets circled the earth, after some careful observations of his own.

This puzzled Kepler, and it was not until after Brahe’s death in 1601, that he made headway in figuring out how the planets interacted with the sun. His sudden breakthrough was the result of his finally being allowed to read the carefully controlled notes Brahe had written. Using these observations and his own ideas he came up with his observations that are now known as Kepler’s three laws of planetary motion.

At first he did believe in Copernicus and his notions of circular motion of the planets around the sun, who himself had corrected the error the world believed about the sun rotating instead of being stationery. It was  Ptolemy, a Greek Astronomer and mathematician who lived and working sometime around 100 A.D. that was responsible for the wrong information.

What led to the discovery that Copernicus was wrong? It was observing Mars with its different movements from the other ground observations that alerted Kepler to the error of  of Copernicus. Although the first thoughts and writing about astronomy were way off course, at least acute scholars did the best they could with their night time vigils of the stars. Each succeeding one built on what the former one had discovered, and it is this method that is still in practice today.

The first law is the law of ellipsis: “The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus.” What he meant by that is the planets indeed does rotate but it does so elliptically.

That is the path around the sun is in a cone shape. To visualize that imagine an imaginary line with its point always pointed toward the sun. The other point would be movable but directly opposite the sun. The amount of light shining on the moving object or planet would be the same at all time. Actually, something similiar to a flash light. The closer to the source of the light the brighter the light, but farther way the light broadens  and is less bright.

The second law is the law of equal areas: “An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. The flash light theory might work here as way of description. The amount of light from the sun on the planet as it rotates is in equal amounts and time and space, although since the planet is moving, the surface that is receiving the sunshine is forever changing.

The third law is the law of Harmonies:  “The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun.” This law at first glance is interpreted as meaning Kepler believed that the planets were equal in and of themselves. That what pertained to one pertained to the other.

True, that if two squares of intersecting squares – where planets might be rotating and blocking the light from the sun of another as their rotations intercepted the other, if they were of equal distances from the sun they would have equal amounts of sun. Whatever, to continually argue over what Kepler meant by his laws is now futile since these laws have likewise been disproved.

If that is so, why then are they still used? They add to the history of the field of astronomy, it is another stepping stone forward, and these laws are still useful in pointing the way to better understanding the motion of the planets and stars.