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Chapter 22: Origins of Modern Astronomy 22.1: Early Astronomy Ancient Greeks and Astronomy • Astronomy is the science that studies the universe. • The first accurate European astronomers were the ancient Greeks. Aristotle (384 - 322 B.C.E.) concluded that the earth was round because it always cast a curved shadow when it passes between the sun and the moon. Aristotle’s belief that the Earth is round was abandoned by the Middle Ages. Aristotle’s Geocentric Universe Eratosthenes (276 – 194 B.C.E.), an ancient Greek mathematician, calculated that the earth’s circumference is 39,000 kilometers - very close to our own modern measurement of 40,075 km. https://youtu.be/G8cbIWMv0rI Calculating Earth’s Circumference The Greeks thought that the Earth was a sphere that stayed motionless at the center of the universe. The other planets and stars revolved around the Earth on their own hollow spheres. The Geocentric Model • In this model, the moon, sun, and the known planets – Mercury, Venus, Mars, Jupiter and Saturn – orbit earth. • Every other body in space circled this system on their own transparent, hollow sphere. • This was called the celestial sphere. A modern version of an earthcentered system. The Heliocentric Model • Aristarchus (312-230 B.C.E.) was the first Greek to believe in a sun-centered, or heliocentric, universe. • In the heliocentric model, Earth and other planets orbit the sun. The Renaissance and the Heliocentric Solar System Aristarchus was condemned by his own religious leaders for his theory. Modern Greece, however, honors him, and even puts his theories on stamps… The Ptolemaic System • Claudius Ptolemy (c. 90 – 168 C.E.) is our main source for what the ancient Greeks knew about astronomy. • He also attempted to explain retrograde motion, or how each planet appears sometimes to stop in the night sky, reverse direction, and then resume eastward motion. Retrograde Motion Ptolemy was wrong – the planets do not orbit Earth. Yet although he used the geocentric model, he did try explain the planets’ apparent motions. The Birth of Modern Astronomy • The first great astronomer after the Greeks was Nicolaus Copernicus (1473-1543) of Poland. • Copernicus proposed the heliocentric model of the solar system: Earth is a planet and all planets of the solar system revolved around the sun at its center. Copernicus’ Axioms 1. 2. 3. 4. There is no one center in the universe. The Earth’s center is not the center of the universe. The center of the universe is near the Sun. The distance from the Earth to the Sun is imperceptible compared with the distance to the stars. 5. The rotation of the Earth accounts for the apparent daily rotation of the stars. 6. The apparent annual cycle of movements of the Sun is caused by the Earth revolving around it. 7. The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes. Copernicus • Since he knew that his book De Revoltionibus would be considered heresy, Copernicus had it published by a friend after his death. • He also pointed out gaps in Ptolemy’s model . Copernicus • Despite the improvement in the model of the universe, he still believed in the idea of perfect circular orbits. • This made his predictions no more accurate than Ptolemy’s and led to doubts about his theory. • Although the Church condemned the book, the damage was already done and the world was opened to new was of thinking about the world. Heliocentric Model of the Solar System Christopher Clavius • 1538 to 1612 • Astronomer for Pope Leo X. • Clavius determined that the Julian Calendar was adding 3 days too many over a period of 385 years. • This caused the date of Easter to slip against the calendar. • That’s a bad thing!! Christopher Clavius • Clavius made (2) proposals: 1. The day following Wednesday October 4th 1582 should be called Thursday October 15th 1582 2. Leap years occur in all years divisible by 4 but in years ending in “00” must be divisible by 400 to called a leap year. – 1600, 2000 yes – 1700, 1800, 1900, 2100 No Pope Gregory X is credited for instituting the new Calendar and today it is known as the Gregorian Calendar. Tycho Brahe • 1546 to 1601 • Tycho studied medicine, law, mathematics, astronomy, and politics. • A supernova seen in 1572 turned his attentions toward astronomy permanently. • He constructed observatories at Hven • After closing Hven due to the political environment, he became the Imperial Mathematician to the Holy Roman Empire in Prague. Tycho Brahe • Tycho was a great maker of astronomical instruments. • He was able to measure the positions of hundreds of stars to within 4’. • Because he found great errors in the Alphonsine tables he decided to create his own Rudolphine Tables • He measured the positions of the planets to within 2’. Tycho Brahe • Tycho had devised his own unique model of the universe where the moon and the sun revolved around the Earth but all of the planets went around the Sun. • He hoped to use his data tables to prove his hypothesis Tycho Brahe • Kepler applied to work at Tycho’s observatory. • Tycho recognized his talents quickly and set him to work on the Rudolphine tables with the purpose of finding the laws of planetary motion. • Unfortunately Tycho died less than two years later, before Kepler worked out his first two laws. (1601) Giordono Bruno • 1548 to 1600 • He was an ordained priest by the Catholic Church. • He believed in many heretical ideas. • Here are just a few: – He believed that there was no center to our universe – the universe was infinite. – He believed other stars were suns – He believed in atoms Giordono Bruno • He believed in atoms • Because of his views, he was persecuted by many different churches and peoples. • Ultimately he went back to face trial in the Vatican. • The trial lasted 7 years before he was found guilty and sentenced Giordono Bruno Giordono Bruno Giordono Bruno • Giordano Bruno was publicly burned at the stake on Feb 17th, 1600. • This was the year of the Jubilee celebration. • Bruno was easily 200 years ahead of his time. Johannes Kepler (1571-1630) was Brahe’s assistant, and later the first important modern astronomer. Kepler applied mathematics to Brahe’s findings and discovered Three Laws of Planetary Motion. • First Law: The path of each planet around the sun is an ellipse, with the sun at one focus. How is an ellipse different from a circle? • A circle is a closed curved shape that is flat. In a circle, all points on the circle are equally distant from the center of the circle. •An ellipse is also a closed curved shape that is flat. •Instead of having all points the same distance from the center (like a circle), an ellipse has two focus points. • Second Law: Kepler determined that a planet travels most rapidly when it comes closest to the Sun and moves slowest when farthest away. Planet Revolution Third Law: Keppler’s third law gives the precise relation between the distance of a planet from the Sun and how fast it completes an orbit, using Astronomical Units (AU). One AU equals 150 million km, the average distance of the Earth from the Sun. http://www.slideshare.net/simonandi sa/94-orbital-motion-keplers-thirdlaw Galileo Galilei • 1564 to 1642 • Very talented mathematician • Excellent experimenter and astronomer • Originally trained in medicine but never completed the degree Galileo Galilei • Strong believer in the Copernican system. • Understood that an object that is dropped will fall straight down, not left behind because of the Earth’s rotation! • Used a telescope to look at the heavens and made improvements in quality and magnification. Galileo Galilei • Galileo wrote a book in Italian about the new evidence for the Copernican system. • He ultimately faced the Inquisition and was force to renounce the Copernican system Galileo Galilei • He was sentenced to house arrest for the last ten years of his life. • During that time he wrote his most complete argument for the Copernican system. • Galileo not only provided evidence that proved the heliocentric model accurate, but he also invented pendulum clocks and the modern thermometer. • He also created one of the first telescopes, without anything but a written description to guide him. He even ground glass for its lenses himself. Galileo used his telescope to view the universe in a new way. He made important discoveries that supported Copernicus’ heliocentric model of the universe. 1. The discovery of the largest four moons of Jupiter. (He also discovered Saturn’s rings.) 2.Planets are NOT pinpoints of light. They are actually spheres, like Earth. 3. Venus has phases, just like the moon. Therefore, Venus circles the Sun. 4, The moon’s surface is not smooth. (Galileo thought the moon’s dark areas might be seas.) 5. The sun has sunspots, or dark regions. Galileo tracked the movement of these sunspots and estimated the rotational period of the sun. Isaac Newton • 1643 to 1727 • Born and raised on a farm, Newton was relatively useless as a farm hand. • He showed great promise in school and later attended Trinity college in London where he graduated with a degree in math in 1665 Isaac Newton • The college was shut down for two years due to the plague so Newton returned home to the farm. • Here he formulated some of his greatest achievements. • These include: Isaac Newton • The Law of Universal Gravitation • Invention of Calculus • 3 Laws of Motion • Optical advancements • Nature of light and the spectrum Isaac Newton • 3 Laws of Motion 1. All objects resist changes in their state of motion unless acted on by an outside net force (law of inertia) Isaac Newton • 3 Laws of Motion 2. If an object is acted on by an outside net force, it will accelerate according to the following formula a=F/m Isaac Newton • 3 Laws of Motion 3. For every force there exists an equal and opposite force often called action-reaction law Isaac Newton • Law of Universal Gravitation • Newton’s great revelation was that the same force that pulls an apple toward the surface of the Earth is the same force that holds the moon in orbit Universal Gravitation 1. Every body in the universe attracts every other body with a force directionally proportional to their masses. 2. Gravitational forces decrease with distance. 3. The greater the mass of the object, the greater its gravitational force. Gravity’s Influence on Orbits Isaac Newton GM1M2 F = ----------------r2 Newton imagined a cannon fired from high mountain. With enough speed the falling cannon ball would match the curve of the earth and remain at the same height above the surface, returning to the cannon from the other side Isaac Newton • After returning to Cambridge University as a professor, He became the Lucasian Professor of Mathematics. 1669 • This position is held by Steven Hawking today Isaac Newton • Newton was later hired as the head of the British mint. • He was in charge of finding and prosecuting counterfeiters • He often went undercover and ultimately convicted more than 10 counterfeiters who were executed Isaac Newton • Newton conducted hundreds of experiments on light and discovered the origin of the spectrum created by prisms • Newton also invented the reflecting telescope Isaac Newton • Much of Newton’s life was filled with controversy. • He fought with many other scientists and mathematicians over who was the discoverer of various ideas. • These included Leibnitz (calculus) and Hooke (optics) and several others. Isaac Newton • Newton is often credited as the greatest scientist of all time. • He impacted more areas of science and even invented an entire branch of mathematics called calculus. • He was knighted among his many honors and served as president of the Royal Society (a scientific watchdog) • He was ill for the last two years of his life and was buried in Westminster Abbey after his death. Isaac Newton Famous Quotes “If I have seen further it is by standing on the shoulders of giants” “I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me”