Chapter 3- The Science of AstronomyThe ancient roots of ScienceMonday, January 14, yChapter 3- The Science of Astronomy The ancient roots of Science• Daily time keeping• tracking seasons and calendar• monitoring lunar cycles• monitoring planets and stars• predicting eclipses• navigation-Days of the week were named for the Sun, Moon and 5 visible planets-Ancient Greek Science• They used Math• THey friend to explain patterns in nature without resorting to myth or the supernatu-ral• they compared with observations• Greeks were the first people known to make models of nature• Greeks developed a Geocentric Model-Plato- heavens must be perfect objects moving on perfect spheres or in perfect circles-Aristotle- Gravity pulls things toward the center of the universe; Earth is at the center of the universe1Monday, January 14, y-Ptolemy- Developed an Earth Centered model that lasted for 1,500 yrs• Most sophisticated geocentric model was the ptolemaic Model-explained retrograde motion of planets by having planets orbiting the Earth on circles on circles-Sufficently accurate to remain in use for so long-Planets orbiting in circles on circles will appear to move backwards, occa-sionally explaining retrograde motion-Correctly predicted planetary positions and eclipses for more than 1000 years• Earth centered universe was eventually adopted by the Catholic/protestantchurches as theology by 1500s.-Copernicus• by 1500s Predictions of ptolemy’s model were noticeably inaccurate• Proposed a sun centers model-Model was no more accurate that Ptolemaic model in prediction planetary positions because it still used perfect circles-Tycho Brahe• Discovered a nova, meaning new star• began to dispel the idea that the heavens were perfect-Johannes Kepler• Hired by Tycho Brahe2Monday, January 14, y• discovered discrepancies could be reconciled by assuming planets orbit in el-lipses not circles• Led to Keplers 3 laws of planetary motion-What’s an elipse• looks like n elongated circle-Its’ eccentricity describes how non-circular it is…. -# 0-1• Know Foci and Semimajor axis and that eccentricity is a measure of how elongated-Semimajor axis- essentially the radius of an ellipse at the point where the distance is furthest from center-Eratosthenes Measures earth• Measurements Syene to Alexandria’s distance is about 5000 stadia at an angleof 7 degrees• 7/360x (circum. Earth)= 5000 Stadia-Circum. Earth= 5000 X 360/7 stadia is about 350,000 Stadia-Kepler’s 3 laws of planetary motion• Kepler’s 1st Law-The orbit of each planet around the sun is an ellipse why the sun agh one focus• Kepler’s 2nd Law3Monday, January 14, y-As a planet moves around it’s orbit, it sweeps out equal areas in equal times.• A planet travels faster when it is nearer the the sun and slower when it’s further away from the sun.• Kepler’s 3rd law-More distant planets orbit the sun at slower average speeds obeying this relationship: p2=a3-p= Orbital period in years-a= avg. distance from the Sun in AU• Not necessarily mathematically sound… Office hours -Objections to Sun-Centered Model• Earth could not be moving because objects in air would be left behind• Non-circular orbits are not perfect as heavens must be.-Galileo Galilei-Helped overcome objections to Earth centers model…….• Scientist and Astronomer- he was the first to use a telescope to look at he sky in 1609• Overcoming objection 1 (nature of motion-Aristotle thought all objects naturally come to rest but galileo showed that ob-jects will stay in motion unless a force acts to slow them down (Newton’s firstlaw of motion)4Monday, January 14, y• Objection 2 (heavenly perfection)-Galileo made a number of important observations with a telescope• There are mountains and valleys on the moon…. imperfections• The sun has spots…..imperfections-Remember the darker spots are the colder areas• 4 moons orbiting Jupiter, proving that not all objects orbit the Earth.• Observed the phases of Venus… only explainable if it orbits the sun and not Earth-Catholic Churched him to recant his claim that Earth orbits the sun in 1633-Spent the rest of his life under house arrest-Galileo for formally vindi-cated by the church in 1992The Nature of Science-Attempts to explain observations based on natural causes-Explanations should be as simple as possible• Occum’s Razor “All things being equal the simplest solution is the best”5Monday, January 14, y-Must make testable predictions and muse be revised if disagrees with observations.-in Science, theories are not just guesses or hypotheses• It must be scientific and must be supported by a large, compelling collection of evi-dence.Astrology verses Astronomy-Astronomy is a science focused on learning about the properties of stars, planets and other celestial objects-astrology is a search for hidden meaning in the movement of the stars• Does astrology have any scientific validity-scientific tests have show they are no more accurate than we should expect from pure