Galileo and Aristotle
Four hundred years ago, an Italian mathematics professor named Galileo Galilei unwittingly made a dramatic career change when he turned his new telescope skyward and became the world’s first telescopic astronomer.
Four hundred years ago, an Italian mathematics professor named Galileo Galilei unwittingly made a dramatic career change when he turned his new telescope skyward and became the world’s first telescopic astronomer.
But Galileo didn’t merely marvel at the never-before seen sights in the night sky. He gave serious, and often ingenuous thought, to what he saw, and began making discoveries and inferences that profoundly changed our view of the cosmos and our place in it, and in so doing, firmly affixed his lauded place in history.
The 17th century scholarly view of the cosmos was still dominated by the teachings of the Greek philosopher Aristotle (384-322 BCE). And many of his ideas about the nature of things, being more akin to beliefs and conjectures than observation-based science, came to be incorporated into the dogma of Christian religion. Thus, in both academia and the church, Aristotle’s world view carried great weight for the better part of two millennia.
The Aristotelian view saw the Earth and all things earthly as composed of four substances: earth, water, air, and fire. Thus the things of our world — the realm of imperfect humans — were imperfect, changing, and subject to death and decay.
All heavenly bodies beyond Earth were composed of a substance not found on Earth called aether (or quintessence) which was perfect, eternal, and unchanging — indeed, godly. Heavenly things were perfectly round with perfectly smooth surfaces; the eternal heavens were fixed and unchanging; and with Earth at the center of the universe, all heavenly objects orbited Earth in perfectly circular orbits.
It was probably not his original intent, yet Galileo and his telescope began to dismantle this world view piece by piece. Each discovery seemed to refute a key element of the Aristotelian view, and in so doing, challenged the official teachings of the Roman Catholic Church, ultimately getting Galileo in big trouble.
In December 1609, Galileo began his study of the heavens by focusing first on the Moon. Next time, we’ll see what he found and which part of Aristotle’s world view took the first hit.
[Much of the above information is from Stephen P. Maran and Laurence A. Marschall’s highly recommended book, Galileo’s New Universe, which was recently reviewed in this column; my Web site contains an archive of previous columns.]
· Sky Calendar
* Dec. 13 Sun. all night: The Geminid meteor shower peaks with no Moon interference.
* 16 Wed.: The Moon is new.
* 20 Sun. evening: The crescent Moon is below Jupiter tonight and above it tomorrow evening.
* 21 Mon.: Winter solstice, the Northern Hemisphere’s first day of winter and shortest day of year after which days begin lengthening for six months.
* 22 Tue. all night: The Ursid meteor shower peaks with the best viewing after the Moon sets around 11 p.m.
* 24 Thu.: The Moon is at 1st quarter.
* 31 Thu.: The second full Moon of the month, popularly called a Blue Moon although it has nothing to do with its color; there will be a slight partial lunar eclipse not visible over the U.S.
· Naked-eye Planets. (The Sun, Moon, and planets rise in the east and set in the west due to Earth’s west-to-east rotation on its axis.) Evening: Jupiter is the brightest object in the southwest; Mercury is near the west southwestern horizon at dusk. Morning: Saturn is high in the southeast with Mars even higher in the southwest. Venus is all but lost in the glare of the rising Sun.
· Astro Milestones. Dec. 14 is the 463rd birthday of Danish astronomer Tycho Brahe (1546-1601) whose meticulous observations and records of Mars’ movement over many years enabled Johannes Kepler to discover elliptical orbits. Dec. 25 is the 367th birthday of the English scientist Isaac Newton (1642-1727), father of modern physics and discoverer of gravity. Dec. 27 is the 438th birthday of the German mathematician Johannes Kepler (1571-1630).
(Stargazer appears every other week. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, 76707, (254) 753-6920 or paulderrickwaco@aol.com. See the Stargazer Web site at stargazerpaul.com.)
