ASTR 101 Lecture 4 Outline of Last Lecture I. Days and SeasonsA. Summer SolsticeB. Winter SolsticeC. Spring EquinoxD. Fall EquinoxII. Phases of the MoonIII. EclipsesOutline of Current Lecture I. The Scientific Thinking of AstronomyII. Astronomical Observations Benefiting Ancient SocietiesA. Ancient civilizations’ achievements in astronomyIII. Greek RootsIV. Copernicus, Tycho, and KeplerA. Kepler’s three laws of planetary motionB. How did Galileo solidify the Copernican revolutionCurrent LectureChapter 3: The Science of Astronomy- Scientific thinking is based on everyday ideas of observation and trial-and-error experiments.- How did astronomical observations benefit ancient societies?o For practical purposes including agricultureo For religious and ceremonial purposeso In aiding navigationo In keeping track of time- Ancient people of central Africa (6500 B.C.) could predict seasons from the orientation of the crescent moon.- What did ancient civilizations achieve in astronomy?o Daily timekeeping (ex: Egyptian obelisk) o Tracking the seasons and calendaro Monitoring lunar cycleso Monitoring planets and starso Predicting eclipseso And more… - In what ways do all humans employ scientific thinking?o Scientific thinking involves the same type of trial-and-error thinking that we use in our everyday lives, but in a carefully organized way.- Our mathematical and scientific heritage originated with the civilizations of the Middle East.- Greeks:o Socrates – 469 BC – 399 BCo Plato – Greek philosopher, mathematician, studied under Socrates. o Aristotle- What is an ellipse? An ellipse looks like an elongated circle.Our goals for learning:1. Why does modern science trace its roots back to the Greeks?a. Greeks were the first people known to make models of natureb. They tried to explain patterns in nature without resorting to myths or the supernatural.2. How did the Greeks explain planetary motion?a. Underpinnings of the Greek geocentric model:i. Earth at the center of the universeii. Heavens must be “perfect” – objects move on perfect spheres or in perfect circles.iii. But this made it difficult to explain the retrograde motion of the planets… iv. The most sophisticated geocentric model – the Ptolemaic model: sufficiently accurate to remain in use for 1500 years. So how does this model explain retrograde motion? Planets really do go backward in this model. It had each planet move on a small (imaginary) circle whose center moves around earth on a larger circle.Our goals for learning:1. How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea?a. Copernicus proposed the sun-centered model.b. He used the model to determine the layout of the solar system (planetary distances in AU).c. But… the model was no more accurate than the Ptolemaic model in predicting planetary motions, because it still used perfect circles. d. Tycho Brahe – compiled the most accurate (1 arc minute) naked eye measurements ever made of planetary motions. 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 rotated around the Sun). He hired Kepler, whoused Tycho’s observations to discover the truth about planetary motion.e. Kepler first tried to match Tycho’s observations with circular motion. But an 8-acrminute discrepancy led him eventually to ellipses.2. What are Kepler’s three laws of planetary motion?a. Kepler’s first law: The orbit of each planet around the Sun is an ellipse, with the Sun at one focus.b. Kepler’s second law: As a planet moves around its orbit, it sweeps out equal areas in equal times. *this means the planets move faster closer to the Sun and slower when its farther from the Sun. c. Kepler’s third law: More distant planets orbit the Sun at slower average speeds, obeying the relationship. p2 = a33. How did Galileo solidify the Copernican revolution?a. He overcame major objections to the Copernican view. Three key objections rooted in the Aristotelian view were the following:i. Earth could not be moving because objects in air would be left behind.ii. Noncircular orbits are not “prefect” as heavens should be.iii. If Earth were really orbiting the Sun, we’d detect stellar
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