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The Solar System: Historical Perspective Objectives • After this lesson, students will be able to: – Define the concept of Astronomy – Describe the geocentric model of the solar system. – Recognize how scientists such as Copernicus, Kepler, and Galileo contributed to acceptance of the heliocentric model of the solar system. What do you know about the solar system? ______ ________ Solar System ________ _______ What is Astronomy? • It is the study of outer space and all the objects on it. Why do we study Astronomy? • Natural disasters • Recreation and esthetics • Scientific inquiry and curiosity • Education of an informed society (you !) • Our place in the Universe • Origin and fate of the Universe (Cosmology) • True Science versus science fiction Astrology is NOT a Science • Seeks to discover “hidden knowledge” by the interpretation of omens (like reading tea leaves). • Results are not repeatable. • Predictions are vague and not testable. • Does not incorporate sciences like chemistry and physics. The Roots of Astronomy • Already in the stone and bronze ages, human cultures realized the cyclic nature of motions in the sky. • Monuments dating back to ~ 3000 B.C. show alignments with astronomical significance. • Those monuments were probably used as calendars or even to predict eclipses. Stonehenge • Constructed 3000 – 1800 B.C. in Great Britain • Alignments with locations of sunset, sunrise, moonset and moonrise at summer and winter solstices • Probably used as calendar. Other Examples around the World Caracol (Mexico); Maya culture, approx. A.D. 1000 Passage of astronomical knowledge Ancient Babylon Ancient Egypt Ancient Roman Empire Ancient Greece Ancient Times Greeks • Many believed Earth was inside rotating spheres nested inside each other, that contained the stars and planets Chinese • Believed Earth was under a dome of stars. Mayans • Other civilizations such as mayans, egyptians, etc. Egyptians Saw patterns in the Sun, moon, and Venus Called the sun “Ra” (Sun god) – rode in his boat across the sky daily Developed 365 day year solar calendar Hipparchus surrounded by his astronomy equipment (drawn centuries later). A Greek astrolabe discovered in the Mediterranean Geocentric Model Ptolemy • Greek astronomer • A.D. 140 • Developed the Geocentric Model Earth was the center, and the other planets and stars revolve around it. It was accepted for nearly 1,500 years because of it’s accuracy at explaining the motions overserved in the sky. Geo = Earth Centric = center Thought planets moved in perfect circles. Geocentric Model Heliocentric Model Aristarchus • Greek scientist, father of astronomy • Developed the Heliocentric Model Helios = sun Centric = center It was not well received in ancient times because people could not accept that Earth was the center of the universe. Ancient Rome The Romans most important contribution to the field of astronomy is the enforcement of a systematic calendar that would account for fact that the year is about ¼ of a day more 365 days. The astronomers of Julius Caesar convinced him to create the Julian Calendar which adds one day to the calendar every 4 years to account for the time we had skipped. This is known as a “leap year”. Heliocentric Model Nicolaus Copernicus (1473-1543) • Developed the Heliocentric Model in detail • Described the arrangement of the known planets of the time and how they moved around the sun. • Published it in 1543 • At first, people were skeptical, but then his theory revolutionized the science of astronomy • Thought planets moved in perfect circles. Heliocentric Model Geocentric or Heliocentric? • Of the early philosophers, only Hipparchus favored the heliocentric model • Most philosophers thought that the evidence supported the Geo model more than the Helio model • What was the evidence? Let’s Look…. Geocentric Evidence • Everything appears to revolve around the Earth each day (diurnal motion). • There is no observable parallax of the stars, planets, Moon, or Sun. • The motions of the stars and heavens are perfect circles. • The heavens were unchanging but the Earth was not. Problems With the Geocentric Model • The planets appear to change brightness, implying a change of distance. • The planets undergo retrograde motion (they move backwards compared to the direction the Sun moves). • The Sun, Moon, and Planets do not move at the same speed all the time. • Mercury and Venus are never seen at opposition (they always appear close to the Sun. Evidence of the Heliocentric Model • The changing brightness of the planets is explained by the Earth getting closer and farther from the planets during our orbit of the Sun. • Our passing planets explain the retrograde motion of the outer planets. • Mercury and Venus are not seen at opposition because they orbit the sun, just as we do. Problems with the Heliocentric Model • The changing speeds of the Sun, Moon, and planets is not explained by simply placing the Sun at the center of the universe. • We do not feel the Earth moving or the atmosphere being pulled away as we fly around the Sun. • If the Earth were spinning, wouldn’t we be thrown off into space? • Why is there no parallax due to our spin or our orbit? Heliocentric Model Tycho Brahe and Johannes Kepler • Worked together • Brahe was a Dutch astronomer that made more accurate observations of the movement of the planets • Kepler was his assistant and used Brahe’s observations to figure out the shape of planet’s orbit. • Kepler described the orbit of each planet as an ellipse. • Ellipse= oval shape Kepler After Tycho’s death, Tycho’s family sued to recover instruments and books of observations Why? Kepler was a Copernican, and they knew he wouldn’t follow the Tychonic system Kepler kept the books! Began to study motion of Mars … Kepler’s First Law of Planetary Motion Orbits are elliptical (oval shaped), sun is at the focus Kepler’s Second Law of Planetary Motion A line from a planet to the sun sweeps over equal areas in equal times Planets travel at different speeds – due to pull of gravity Closer to Sun, moves faster… Why? Same time, moves slower Kepler’s Model (the elliptical orbit) Heliocentric Model Galileo Galilei • Italian scientist • 1500’s- 1600’s some people still believed in the geocentric model. • Collected enough evidence to convince others of the heliocentric model. • 1610, used a telescope to discover four moons around Jupiter. • • The movement of those moons around Jupiter proved that not everything revolves around Earth. In conclusion, the geocentric model must be incorrect. Isaac Newton (1643 - 1727) • Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler • Major Achievements: – Invented Calculus as a necessary tool to solve mathematical problems related to motion – Discovered the three laws of motion – Discovered the universal law of mutual gravitation Hipparchus Claudius Ptolemy Nicolas Copernicus 85 – 165 AD 1473 – 1543 Sir Isaac Newton Edmund Halley Sir William Herschel Caroline Herschel Albert Einstein Edwin Hubble 1642 – 1727 1656 – 1742 1738 – 1822 1750 – 1848 1879 – 1955 1889 – 1953 190 – 120 BC Tycho Brahe 1546 – 1601 Johannes Kepler 1571 – 1630 Galileo Galilei 1564 – 1642 References Earth Science, Interactive Science. (2013). Saddle River, New Jersey: Pearson Education, Inc.