Louis Lackey Day 4

 Miss Blazejack is a genius.

Astronomy

Day 4

We began by briefly passing around Skywatchers of Ancient Mexico and Science Magazine August 2011. “Skywatchers” is relevant to 2012 and the Mayan civilization. The Science Magazine article is relevant to life in the universe.

The goals of the chapter are on page 56.

Section 3.1 is about the ancient roots of science. All human beings employ scientific thinking through observation and trial and error. Ancient societies used astronomy to keep track of time, the seasons for agriculture, for religious purposes and for aiding navigation. Ancient people in Africa in 6500 BC could predict seasons by the orientation of the crescent moon. They considered the tilt compared to the horizon, and visualized it as a pair of horns. Ancient civilizations named the days of the week after visible astronomical objects; Sunday, Monday, etc. Ancient Civilizations achieved timekeeping, calender, monitoring the moon and stars, predicting eclipses, and more. An Egyptian Obelisk functions as a sundial to tell the time of the day. There are numerous other examples of civilizations all over earth constructing structures that manipulate astronomical phenomena.

Section 3.2 is about the Ancient Greeks. Our western scientific heritage originated in the middle east. The Greeks learned from the middle east and Egypt. The Greeks were the first to make models of nature. They tried to explain patterns in nature without myth or the supernatural. Eratosthenes measured the entire earth using trigonometry with accuracy in 240 BC. Plato and Aristotle placed the earth at the center of the universe with a series of perfect spheres moving in perfect circles. Ptolemy made the Ptolemaic model (ad 100-170). It was used for 1500 years because of its accuracy, the Arabs called it the greatest compilation (almagest). It was based on planets moving in circles around a circle, to explain retrograde orbit. The Muslim world preserved and enhanced Greek science while Europe went through the dark ages. Al-Mamun's house of wisdom in Baghdad was a great library around ad 800. When Constantinople fell in 1453 Eastern scholars headed west into Europe carrying knowledge that sparked the Renaissance.

Section 3.3 is about the Copernican Revolution. Before Galileo astronomy was all theoretical, he began observing (with a telescope) and measuring. Copernicus proposed a sun centered model in 1543. He used it to determine the layout of the solar system with planetary distances. The model was closer to the truth but not accurate because it still used perfect circles. Tycho Brahe compiled the most accurate naked eye (1 arc-minute) measurements. He could not determine parallax and still thought the earth was the center, but that the other planets went around the sun. He hired Kepler, who used Tycho's work to discover the truth of the solar system. An 8 arc-minute discrepancy led Kepler to discover ellipses. Kepler had three laws of planetary motion. First, the orbit of each planet around the sun is an ellipse with the sun at one focus, nothing lies at the other focus. Second, as a planet moves around its orbit, it sweeps out equal areas in equal times. A planet moves faster when it is closer to the sun. Third, more distant planets orbit the sun at slower speeds obeying the relationship p^2=a^3, p= orbital period in years, a= average distance from sun in AU. Galileo overcame three objections to Copernicus. Earth could not be moving because objects falling would be left behind by the moving earth, non-circular orbits are not perfect, as a perfect heavens should be, and if the earth were really orbiting the sun, we would detect parallax.

We will finish section 3.4 next week.