Jessie Horn Chapter 3 Notes

Chapter 3: The Science of Astronomy
3.1 The Ancient Roots of Science
Learning Goals:

1. In what ways do all humans employ scientific thinking? Answer: Scientific thinking is based on everyday ideas of observation and trial-and-error experiments.
2. How did astronomical observations benefit ancient societies? Answer: In keeping track of time and seasons, for practical purposes, including agriculture, for religious and ceremonial purposes, and in aiding navigation.

Ancient people of central Africa (6500 BC) could predict the seasons from the orientation of the crescent moon. The days of the week were named for the Sun, Moon, and visible planets.

What did ancient civilizations achieve in astronomy?

• Daily timekeeping
• Tracking seasons and calendar
• Monitoring lunar cycles
• Monitoring planets and stars
• Predicting eclipses
• And more...

Scientific thinking involves the same type of trial-and-error thinking that we use in our everyday lives, but in a carefully organized way. 

3.2 Ancient Greek Science

1. Why does modern science trace its roots to the Greeks? Answer: Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or supernatural Greek geocentric models (c. 400 BC).
2. How did the Greeks explain planetary motion? Answer: Underpinnings of the Greek geocentric model: Earth is at the center of the universe, Heavens must be "perfect" - objects move on perfect spheres or in perfect circles. But this made it difficult to explain the apparent retrograde motion of planets...Review: Over a period of 10 weeks, Mars appears to stop, back up, then go forward again. The most sophisticated geocentric model was that of Ptolemy (AD 100-170)- the Ptolemaic model: sufficiently accurate to remain in use for 1500 years, Arabic translation of Ptolemy's work named Almagest ("The greatest compilation"). 
3. How did Islamic scientists preserve (make) and extend Greek science? Answer: The Muslim world preserved and enhanced the knowledge they received from the Greeks while Europe was in its Dark Ages. Al-Mamun's House of Wisdom in Baghdad was a great center of learning around AD 800. With the fall of Constantinople (Istanbul) in 1453, Eastern scholars headed West to Europe  carrying knowledge that helped ignite the European Renaissance. 

Which of the following is NOT a fundamental difference between the geocentric and sun-centered models of the solar system? Answer: The geocentric model is useless for predicting planetary positions in the sky, whereas even the earliest sun-centered models worked almost perfectly, which is false. 

3.3 The Copernican Revolution

1. How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea? Answer: Copernicus (1473-1543) proposed the sun-centered model (published in 1543), he used the model to determine the layout of the solar system (planetary distances in AU), BUT...the model was no more accurate than the Ptolemaic model in predicting planetary positions because it still used perfect circles. Tycho Brahe (1546-1601) compiled the most accurate (1 arcminute) naked eye measurements ever made of planetary positions. He still could not detect stellar parallax and thus, still thought Earth must be at the center of the solar system (but recognized that other planets go around the Sun). He hired Kepler, who used Tycho's observations to discover the truth about planetary motion. Johannes Kepler (1571-1630) first tried to match Tycho's observations with circular orbits. But an 8-arcminute discrepancy led him eventually to ellipses: "If I had believed that we could ignore these 8 mins (of arc), I would have patched up my hypothesis accordingly. But since it was not permissible to ignore, those 8 mins pointed the road to a complete reformation in astronomy." Ellipse: an ellipse looks like an elongated circle.
2. What are Kepler's 3 laws of planetary motion? Kepler's first law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus. Kepler's second law: As a planet moves around its orbit, it sweeps out equal areas in equal times. This means that the planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun. Kepler's third law: More distant planets orbit the Sun slower averages speeds, obeying the relationship. Astronomical Unit = AU. Distance from Earth to the Sun is 8 light minutes.
3. How did Galileo solidify the Copernican revolution? Galileo (1564-1642) overcame major objections to the Copernican view. Three key objections rooted in the Aristotelian view were the following: Earth could not be moving because objects in air would be left behind, Non-circular orbits are not "perfect" as heavens should be, and if Earth were really orbiting the Sun, we'd detect stellar parallax. Overcoming the first objection (nature of motion): Galileo's experiments showed that objects in air would stay with a moving Earth. Aristotle thought that all objects naturally come to rest (wrong), Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton's first law of motion). Overcoming the second objection (heavenly perfection): Tycho's observations of comet and supernova already challenged this idea. Using his telescope, Galileo saw: sunspots on the Sun ("imperfections"), mountains and valleys on the Moon (proving it is not a perfect sphere) overcoming the third objection (parallax). Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. Galileo showed stars must be much farther than Tycho thought, in part by using his telescope to see the Milky Way is countless individual stars. If stars were much farther away, then lack of detectable parallax was no longer so troubling. Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit Earth. Galileo's observations of phases of Venus proved that it orbits the Sun and not the Earth. In 1633, the Catholic Church ordered Galileo to recant his claim that Earth orbits the Sun. His book on the subject was removed from the Church's index of banned books in 1824. Galileo was formally vindicated by the church in 1992. 

3.4 The Nature of Science 

1. How can we distinguish science from non-science? Defining science can be surprisingly difficult. Science, in Latin, means "knowledge." But not all knowledge comes from science. The idealized scientific method is based on proposing and testing a hypothesis, or an educated guess. But science rarely proceeds in this idealized way. For example: sometimes we start by "just looking" then coming up with possible explanations. Sometimes we follow intuition rather than a particular line of evidence. Hallmarks of Science #1: Modern science seeks explanations for observed phenomena that rely solely on natural causes (A scientific model cannot include dive intervention). Hallmarks of Science #2: Science progresses through creation and testing of models of nature that explain the observations as simply as possible (simplicity = "occam's razor). Hallmarks of Science #3: A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.  
2. What is the scientific theory? The word "theory" has a different meaning in science than in everyday life. In science, a theory is NOT the same as a hypothesis. A scientific theory must: explain a variety of observations with a few simple principles  be supported by large, compelling body of evidence, NOT have failed any crucial test of its validity. Darwin's Theory of evolution meets all the criteria of scientific theory. This means after more than 100 years of testing, Darwin's theory stands stronger than ever, having successfully met every scientific challenge to its validity.