James Baquet

    A few months back we talked about Tycho Brahe, he of the “golden” nose. Johannes Kepler (1571-1630) was once his assistant but, like many a disciple, Kepler went on to excel the master. Brahe got many things wrong, but Kepler is remembered best for the principles known today as “Kepler’s laws of planetary motion.”

    Kepler’s parents separated when he was young, and it was his mother who instilled in him a love of astronomy, first by ensuring that he observed the Great Comet of 1577 (when he was just 6), and second for calling him out to see a lunar eclipse three years later. Kepler returned his mother’s kindness near the end of her life, when she was accused of witchcraft. He left his work and moved his family to use his keen scientific mind to achieve her acquittal shortly before her death.

    Now, about those other laws: Kepler had smallpox as a child, which left him with poor eyesight and impaired use of his hands. So he turned to theoretical rather than observational astronomy. Using many of the observations made by Brahe, he determined the following:

    1. The law of ellipses: A planet’s orbit is an ellipse, not a perfect circle as had been previously believed. The sun is one of the two foci of that ellipse.

    2. The law of equal areas: A line joining a planet and the sun will sweep out equal areas in an equal amount of time. (This means the planet moves faster when it’s closer to the sun.)

    3. 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 shows a constant relationship between the period it takes two planets to orbit the sun, and their relative distance from the sun.)

    Kepler’s laws provided an improvement on the previous work by Nicholas Copernicus (1473-1543), and were in turn confirmed and built upon later by Sir Isaac Newton (1642-1727), placing Kepler squarely in the Western scientific tradition.

    Vocabulary:

    Which word above means:

    1. gradually put something into someone’s mind

    2. plural of focus, here meaning “center points”

    3. act of being found not guilty

    4. the way the planets move

    5. a regular oval shape

    6. the practice of “black” magic

    7. event where the earth blocks the sun’s light from the moon

    8. weakened; damaged

    9. dangerous infectious disease that causes high fever and leaves marks on the skin

    10. mathematical relationship