History of Astronomy


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History of Astronomy

  1. 1. The History of Astronomy http://www.phys.uu.nl/~vgent/babylon/babybibl_intro.htm http://mason.gmu.edu/~jmartin6/howe/Images/pythagoras.jpg http://www.russellcottrell.com/greek/aristarchus.htm http://www.mesopotamia.co.uk/astronomer/homemain.html plato.lib.umn.edu/ http://web.hao.ucar.edu/public/education/sp/images/aristotle.html http://web.hao.ucar.edu/public/education/sp/images/ptolemy.html http://www.windows.ucar.edu/tour/link=/people/ancient_epoch/hipparchus.html http://copernicus.atspace.com/ http://www.danskekonger.dk/biografi/andre/brahe.htm/ http://antwrp.gsfc.nasa.gov/apod/ap960831.html http://www.lucidcafe.com/library/95dec/newton.html
  2. 2. Introduction <ul><li>Western astronomy divides into 4 periods </li></ul><ul><ul><li>1. Prehistoric (before 500 B.C. ) </li></ul></ul><ul><ul><ul><li>Cyclical motions of Sun, Moon and stars observed </li></ul></ul></ul><ul><ul><ul><li>Keeping time and determining directions develops </li></ul></ul></ul><ul><ul><li>2. Classical (500 B.C. to A.D. 1400) </li></ul></ul><ul><ul><ul><li>Measurements of the heavens </li></ul></ul></ul><ul><ul><ul><li>Geometry and models to explain motions </li></ul></ul></ul><ul><ul><li>3. Renaissance (1400 to 1650) </li></ul></ul><ul><ul><ul><li>Accumulation of data lead to better models </li></ul></ul></ul><ul><ul><ul><li>Technology (the telescope) enters picture </li></ul></ul></ul><ul><ul><li>4. Modern (1650 to present) </li></ul></ul><ul><ul><ul><li>Physical laws and mathematical techniques </li></ul></ul></ul><ul><ul><ul><li>Technological advances accelerate </li></ul></ul></ul>History of Astronomy
  3. 3. The Model of the Cosmos <ul><li>It’s a natural thing for people to want to understand the world around them. </li></ul><ul><li>People build models, a (simplified?) conceptual framework that represents the real world and operates in a manner consistent with observations. </li></ul><ul><li>To be successful, a model MUST be able to do two things… </li></ul>
  4. 4. Model Building <ul><li>A model must accept and incorporate all careful, accurate observations. No observations may be conveniently discarded, simply because they contradict the model. [The model must be refined!] </li></ul><ul><li>A model must be able to make accurate predictions of future events. </li></ul>
  5. 5. Models Change <ul><li>Take note of how the model of the cosmos changes as new observations become available. </li></ul><ul><li>Take note also of the forces which resisted logical changes: mental inertia, political censorship and religious dogma. </li></ul>
  6. 6. 1. Prehistoric Astronomy <ul><li>The basis of prehistoric astronomy: </li></ul><ul><ul><li>Celestial Sphere </li></ul></ul><ul><ul><li>Rising and setting of Sun, Moon, and stars </li></ul></ul><ul><ul><li>Constellations </li></ul></ul><ul><ul><li>Annual motion of Sun * </li></ul></ul><ul><ul><li>Motion of planets through zodiac </li></ul></ul><ul><ul><li>Phases of the Moon </li></ul></ul><ul><ul><li>Eclipses * </li></ul></ul>History of Astronomy
  7. 7. Practical Uses <ul><li>Ancient Americans were farmers and needed to know the best time for planting and harvesting. </li></ul><ul><li>With farming came a practical need for a calendar. </li></ul><ul><li>As civilization developed, deeper meanings were attached to astronomical phenomenon. </li></ul><ul><li>An overall trend: the more settled a culture became, the more religious meanings became attached to the sky. </li></ul>
  8. 8. The Roots of Astronomy <ul><li>Already in the stone and bronze ages, human cultures realized the cyclic nature of motions in the sky. </li></ul><ul><li>Monuments dating back to ~ 3000 B.C. show alignments with astronomical significance. </li></ul><ul><li>Those monuments were probably used as calendars or even to predict eclipses. </li></ul>
  9. 9. Ancient Astronomy <ul><li>In the beginning, there were 3 basic types of ancient observatories </li></ul><ul><li>Simple markers </li></ul><ul><li>Circles </li></ul><ul><ul><li>Stone, wood, holes, or lines </li></ul></ul><ul><li>Temples or tombs </li></ul><ul><ul><li>Passageways, shafts, windows, or other openings that would face the rising/setting moon, sun or important stars </li></ul></ul>
  10. 10. What did the observatories measure? <ul><li>Solstices </li></ul><ul><li>Equinoxes </li></ul><ul><li>Changes of Seasons </li></ul>
  11. 11. Stonehenge <ul><li>Alignments with locations of sunset, sunrise, moonset and moonrise at summer and winter solstices </li></ul><ul><li>Probably used as calendar. </li></ul>Summer solstice Heelstone <ul><li>Constructed: 3000 – 1800 B.C. </li></ul>
  12. 12. Stonehenge 0
  13. 13. Stonehenge <ul><li>Stonehenge in southern England is believed to be part of an astronomical device which was completed in 2000 B.C. </li></ul><ul><li>A section of its structure called the “avenue” points towards the location at which the Sun rises in the Summer solstice, and other sight lines created by the structure point towards the most northern and southerly risings of the Moon. </li></ul><ul><li>It was not used to track the Moons rising and setting points </li></ul>
  14. 14. Other Examples All Over the World Big Horn Medicine Wheel (Wyoming)
  15. 15. Big Horn Medicine Wheel <ul><li>Arrangement of rocks resembling a 28-spoke wheel in the Big Horn Mountains of Wyoming </li></ul><ul><li>Used as calendar by the Plains Indians from about 1500 – 1700 CE </li></ul><ul><li>Used as indicator of summer solstice sunrise and sunset. </li></ul><ul><li>The alignments are controversial as they could be due to chance </li></ul><ul><li>It was not used to track the Moons rising and setting points </li></ul>
  16. 16. Tomb at Newgrange, Ireland <ul><li>The passage tomb was constructed in such a way that on the Winter solstice light from the rising Sun penetrates the main passage shining into the inner chamber for just 17 minutes in the year. </li></ul><ul><li>Researchers have also discovered evidence that Newgrange may have been designed in order to allow light from the Moon to enter the inner chamber approximately every nine years when the Moon’s path crosses the position that the Winter solstice Sun would occupy. </li></ul>
  17. 18. Caracol (Maya culture, approx. A.D. 1000) Contained window that were aligned with rising point of Venus over the horizon
  18. 19. 2. Classical (500 B.C. to A.D. 1400) <ul><ul><ul><li>Measurements of the heavens </li></ul></ul></ul><ul><ul><ul><li>Distance and Size of the Sun and Moon </li></ul></ul></ul><ul><ul><ul><li>The Shape of the Earth </li></ul></ul></ul><ul><ul><ul><li>The Size of the Earth </li></ul></ul></ul><ul><ul><ul><li>The Motion of the Planets </li></ul></ul></ul>
  19. 20. Passage of astronomical knowledge Ancient Babylon Ancient Egypt Ancient Greece Ancient Roman Empire
  20. 21. Astrology <ul><li>Around 1200-1000 B.C., the Babylonians studied astrology – indeed they invented the 12 signs of the Zodiac that are still used today. Around the same time, the Greeks named most of the stars and constellations in the northern hemisphere (e.g. Hercules, Perseus, Cassiopea, Cygnus). They also named the &quot;the wandering stars&quot;, which we now know to be planets. The Greeks named these after their gods, Mercury, Venus, Mars and Jupiter. </li></ul>I. Babylon
  21. 22. Mesopotamia/Babylon Modern political boundaries Ancient Babylon
  22. 23. II. Egyptian <ul><li>Temple at Karnak </li></ul><ul><ul><li>Certain alignments correspond to summer solstice sunset and winter solstice sunrise </li></ul></ul><ul><li>Pyramid of Khufu at Giza </li></ul><ul><ul><li>Shafts from the King's chamber indicate </li></ul></ul><ul><ul><ul><li>location of Polaris 5000 years ago </li></ul></ul></ul><ul><ul><ul><li>Former position of Orion's belt </li></ul></ul></ul><ul><ul><li>The pyramid is also aligned perfectly N-S and E-W </li></ul></ul>
  23. 24. Karnak
  24. 25. Giza
  25. 26. III. Greek Astronomers <ul><li>Unfortunately, there are no written documents about the significance of stone and bronze age monuments. </li></ul><ul><li>First preserved written documents about ancient astronomy are from ancient Greek philosophy. </li></ul><ul><li>Greeks tried to understand the motions of the sky and describe them in terms of mathematical (not physical!) models . </li></ul>
  26. 27. Ancient Greece
  27. 28. Ancient Greek Astronomers A. Eudoxus (409 – 356 B.C.): Model of 27 nested spheres B. Aristotle (384 – 322 B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: 1. Imperfect, changeable Earth , <ul><li>He expanded Eudoxus’ Model to use 55 spheres. </li></ul>2. Perfect Heavens (described by spheres)
  28. 29. C. Eratosthenes <ul><li>Erathoshenes was able to measure the radius of the earth as early as 200 CE. </li></ul><ul><li>He then calculated the circumference of the Earth to be 25,000 miles which is very close to the real circumference of the Earth. </li></ul>
  29. 30. Eratosthenes’s Experiment
  30. 31. D. Ptolemy Believed the Earth was the center of the universe Believed the sun and planets circle the earth.
  31. 32. Ptolemy’s System <ul><li>Geocentric </li></ul><ul><li>Perfect Circles </li></ul><ul><li>Earth </li></ul><ul><li>Moon </li></ul><ul><li>Mercury </li></ul><ul><li>Venus </li></ul><ul><li>Sun </li></ul><ul><li>Mars </li></ul><ul><li>Jupiter </li></ul><ul><li>Saturn </li></ul><ul><li>Fixed Stars </li></ul>
  32. 33. Ptolemy’s Idea of the Universe Earth is in the center. Planets circle the earth. Sun orbits the Earth .
  33. 34. Ptolemy’s 2 other accomplishments <ul><li>Ptolemy calculated what he believed to be the size of the cosmos : 20,000 earth radii or 134,000,000 kilometers (radius) . </li></ul><ul><li>Ptolemy wrote the first astronomy textbook, the Almagest (the “Majestic Book”). </li></ul>
  34. 35. http://www.er.uqam.ca/nobel/r14310/Ptolemy/Images/Regiomontanus/1496.g.jpg The Almagest
  35. 36. IV. 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”.
  36. 37. Ancient Rome
  37. 38. 3. The Renaissance 1300’s-1500’s
  38. 39. Nicolas Copernicus (1473-1543) <ul><li>Proposed a Heliocentric Universe </li></ul><ul><li>Calculated Relative Distances to Planets </li></ul><ul><li>Copernicus published his ideas in an influential book De Revolutionibus Orbium Coelestium </li></ul>
  39. 40. Heliocentric Universe
  40. 41. Copernicus’s issues with Ptolemy <ul><li>Inner Planets’ deferent = Sun </li></ul><ul><li>Outer Planets’ epicycle = Sun </li></ul>
  41. 42. Let’s put the Earth on an Epicycle
  42. 43. It’s still pretty tricky Ptolemy Copernicus
  43. 44. Problems with the Copernican Model <ul><li>Copernicus’ model was much simpler and more elegant than the geocentric model, and it could be used, through geometry, to accurately measure the distances between the planets and the sun. </li></ul><ul><li>It also explained retrograde motion in a much more natural way. </li></ul><ul><li>But there were still problems. </li></ul><ul><ul><ul><ul><ul><li>Could not predict planet positions any more accurately than the model of Ptolemy </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Could not explain lack of parallax motion of stars </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Conflicted with Aristotelian “common sense” </li></ul></ul></ul></ul></ul>
  44. 45. Let’s put the Earth on an Epicycle
  45. 46. Church resistance <ul><li>Through the centuries, the Church had interpreted several verses of Scripture to indicate that the Earth was the center of the universe. </li></ul><ul><li>Ideas that questioned this Church teaching might lead people to question other teachings, threatening the Church’s religious and temporal power. </li></ul>
  46. 47. Tycho Brahe - An Observer <ul><li>He made a huge number of observations of the stars and planets, all with the naked eye </li></ul><ul><ul><li>Even without a telescope, he was very accurate in his measurements </li></ul></ul><ul><li>He built an observatory called the Uraniborg </li></ul><ul><li>Also recorded the appearance of comets and supernovae </li></ul><ul><ul><li>The Tycho supernova remnant is still visible today </li></ul></ul>Tycho (1546-1601) Tyco Brahe
  47. 48. Uraniborg : Castle of the Heavens
  48. 49. Tycho Brahe observing the supernova in 1572. www.tayabeixo.org/articulos/tycho.htm
  49. 50. Tyco Brahe’s Universe Earth does not move & Lots of Circles
  50. 51. Galileo Galilei (1564-1642) <ul><li>Observed sky with telescope </li></ul><ul><li>Proved Copernicus right!! </li></ul><ul><li>Condemned by Church </li></ul><ul><li>Designed simple experiments about gravity proofing that a heavy and light object fall at the same rate. </li></ul>
  51. 52. Major Discoveries of Galileo <ul><li>Moons of Jupiter </li></ul><ul><li>(4 Galilean moons) </li></ul><ul><li>Rings of Saturn </li></ul>( What he really saw) ( What he really saw) Proofing that Jupiter was more massive then the Earth
  52. 53. Major Discoveries of Galileo <ul><li>Surface structures on the moon; first estimates of the height of mountains on the moon. This suggested that the moon was not prefect </li></ul>
  53. 54. Major Discoveries of Galileo <ul><li>Sun spots (proving that the sun is not perfect!) </li></ul>
  54. 55. Observed Phases of Venus * Galileo Found the Gibbons phase of Venus, which proofed that Venus orbited the Sun
  55. 56. Johannes Kepler (1571-1630) <ul><li>Used Brahe’s data to correctly describe planetary motion </li></ul><ul><li>Stated 3 Laws </li></ul>
  56. 57. Ellipse Focus #1: Planets orbit the Sun in elliptical paths with the Sun at one focus
  57. 58. 4. The Modern age
  58. 59. Isaac Newton (1642-1727) <ul><li>Discovered the Law of Universal </li></ul><ul><li>Gravitation </li></ul><ul><li>Proved Kepler’s 3 Laws </li></ul><ul><li>Newton’s 3 Laws of motion </li></ul><ul><ul><li>First Law A body at rest will remain at rest, unless a force acts on it </li></ul></ul><ul><ul><li>Second Law Force = Mass X Acceleration </li></ul></ul><ul><ul><li>Third Law For every action there is an equal and opposite reaction </li></ul></ul><ul><li>Invented reflecting telescope, calculus, & physics </li></ul>
  59. 60. <ul><li>Newton conducted hundreds of experiments on light and discovered the origin of the spectrum created by prisms </li></ul><ul><li>Newton also </li></ul><ul><li>invented the </li></ul><ul><li>reflecting </li></ul><ul><li>telescope </li></ul>
  60. 61. Edmund Halley (1656-1752) <ul><li>Studied Newton’s theories </li></ul><ul><li>Charted southern hemisphere stars, cataloged @ 341 stars </li></ul><ul><li>Helped Newton publish his book by providing him with financial support </li></ul><ul><li>Noticed that Venus’ path could be seen </li></ul><ul><li>Calculated comet’s orbit demonstrating that comets have an elliptical path around the sun and return to the same point </li></ul><ul><li>Halley’s comet returns every 76 years </li></ul>
  61. 62. Albert Einstein (1879-1955) <ul><li>His parents were originally told he would amount to nothing and was considered to be a failure. </li></ul><ul><li>Won the Noble Prize in 1921 </li></ul><ul><li>Theories of Relativity </li></ul><ul><li>Known mainly for his formula E = mc 2 </li></ul><ul><li>Time and distance are not absolute but relative to the observers frame of reference </li></ul><ul><li>His famous formula relates to the converting of mass to energy and energy to mass. </li></ul>
  62. 63. Edwin Hubble ( 1889-1953) <ul><li>Influential in modern astronomy </li></ul><ul><li>Observed that the universe is expanding </li></ul><ul><li>Classified different galaxies and noted that they were moving away from each other which gave rise to Hawking’s Big Bang Theory. </li></ul><ul><li>Proved that other galaxies existed beyond our galaxy (The Milky Way) </li></ul><ul><li>Astronomy was not recognized so he could not win a Noble Prize; after his death it became recognized </li></ul><ul><li>Hubble Telescope was named in his honor. </li></ul>
  63. 64. Steven Hawking ( 1942- ) <ul><li>Laws that govern the universe </li></ul><ul><li>Big Bang Theory (scientific not the TV show) </li></ul><ul><li>Physics of Black holes </li></ul>
  64. 65. History of Astronomy The sphere of the sky surrounds the Earth and is called the “celestial sphere.” Back
  65. 66. History of Astronomy The two constellations Leo, (A), and Cygnus, (B), with figures sketched in to help you visualize the animals they represent. (Photo (A) from Roger Ressmeyer, digitally enhanced by Jon Alpert. Photo (B) courtesy Eugene Lauria.) Back
  66. 67. History of Astronomy The Sun hides from our view stars that lie beyond it. As we move around the Sun, those stars become visible, and the ones previously seen are hidden. Thus the constellations change with the seasons. Back
  67. 68. History of Astronomy The Earth's rotation axis is tilted by 23.5° with respect to its orbit. The direction of the tilt remains the same as the Earth moves around the Sun. Thus for part of the year the Sun lies north of the celestial equator, whereas for another part it lies south of the celestial equator. Back
  68. 69. History of Astronomy These five diagrams show the Sun's position as the sky changes with the seasons. Although the Earth moves around the Sun, it looks to us on the Earth as if the Sun moves around us. Notice that because the Earth's spin axis is tilted, the Sun is north of the celestial equator half of the year (late March to late September) and south of the celestial equator for the other half of the year (late September to late March). Back
  69. 70. History of Astronomy The direction of the rising and setting Sun changes throughout the year. At the equinoxes the rising and setting points are due east and west. The sunrise direction shifts slowly northeast from March to the summer solstice, whereupon it shifts back, reaching due east at the autumn equinox. The sunrise direction continues moving southeast until the winter solstice. The sunset point similarly shifts north and south. Sunrise on the summer solstice at Stonehenge. (Courtesy English Heritage.) Back
  70. 71. History of Astronomy (A) The cycle of the phases of the Moon from new to full and back again. (B) The Moon's phases are caused by our seeing different amounts of its illuminated surface. The pictures in the dark squares show how the Moon looks to us on Earth. Back
  71. 72. History of Astronomy A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Moon's shadow strikes the Earth. The photo inset shows what the eclipse looks like from Earth. (Photo courtesy of Dennis di Cicco.) Back
  72. 73. History of Astronomy A lunar eclipse occurs when the Earth passes between the Sun and Moon, causing the Earth's shadow to fall on the Moon. Some sunlight leaks through the Earth's atmosphere casting a deep reddish light on the Moon. The photo inset shows what the eclipse looks like from Earth. (Photo courtesy of Dennis di Cicco.) Back
  73. 74. History of Astronomy (A) During a lunar eclipse, we see that the Earth's shadow on the Moon is curved. Thus the Earth must be round. (B) As a traveler moves from north to south on the Earth, the stars that are visible change. Some disappear below the northern horizon, whereas others, previously hidden, become visible above the southern horizon. This variation would not occur on a flat Earth. Back
  74. 75. History of Astronomy Eratosthenes's calculation of the circumference of the Earth. The Sun is directly overhead on the summer solstice at Syene, in southern Egypt. On that same day, Eratosthenes found the Sun to be 7° from the vertical in Alexandria, in northern Egypt. Eratosthenes deduced that the angle between two verticals placed in northern and southern Egypt must be 7°. Back
  75. 76. History of Astronomy Aristarchus used the size of the Earth's shadow on the Moon during a lunar eclipse to estimate the relative size of the Earth and Moon. Back
  76. 77. History of Astronomy How to determine linear size from angular size. Back
  77. 78. History of Astronomy Aristarchus estimated the relative distance of the Sun and Moon by observing the angle A between the Sun and the Moon when the the Moon is exactly half lit. Angle B must be 90° for the Moon to be half lit. Knowing the Angle A, he could then set the scale of the triangle and thus the relative lengths of the sides. Back
  78. 79. History of Astronomy Motion of the Earth around the Sun causes stellar parallax. Because the stars are so remote, this is too small to be seen by the naked eye. Thus the ancient Greeks incorrectly deduced that the Sun could not be the center of the Solar System. Back
  79. 80. History of Astronomy Cutaway view of the geocentric model of the Solar System according to Eudoxus. (Some spheres omitted for clarity.) Back