The Earth’s Motion

1. The Earth’s Motion Chapter 2

2. Does the Earth Move • How do we know that the earth is moving? • How do you know that when in a car that the car is moving? • If the earth is moving why don’t we fall off?

3. The Geocentric Theory • The earth is the center and the universe moves around the earth. • Ancient astronomers found seven heavenly objects that were different: • Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn (in that order) • These objects moved slowly among the stars, which were the outermost layer

4. The Geocentric Theory • Ancient astronomers believed that the sun’s sphere turned once each day. • The other planets turned nearly once each day, but at slightly different rates. • This explained the independent paths of the planets. • The moon’s sphere turned much more slowly allowing it to change position rapidly. • Explained why the moon rises about 50 minutes later each night.

5. Geocentric Scientists • Hipparchus – Greek astronomer around 190-120 BC. • Created one of the earliest catalogs of 850 stars. • Developed a mathematical geocentric model.

6. Geocentric Scientist • Ptolemy – a.k.a Cladius Ptolemaeus – AD 85-165 - Alexandrian (Egyptian) astronomer. • Presented the geocentric theory in a large collection of writing titled The Greatest Compilation – a.k.a. Almagest • Geocentric theory is sometimes referred to as the Ptolemaic theory because he played such a large role in attempting to improve the theory.

7. Problems with Geocentric Theory • The Planets sometime appear to be large, bright, and close compared to other times when they seem smaller, dimmer, and farther away. • Ptolemy tried to shift each planet so that the earth was no longer the center causing an eccentric (off-center circle). • Astronomers were offended by this because it was not a symmetrical and in their eyes not a beautiful…but it did make the model closer to the observations.

8. Problems with Geocentric Theory • Model also could not explain why it appeared that planets had retrograde motion. • Planets slowed down, stopped, and then appeared to back up. • The planets would trace a backward loop and then resume their forward motion.

9. Problems with Geocentric Theory • Ptolemy explained • retrograde motion by imagining that each planet moved in small circles called epicycles. • The planets continued to revolve around the earth also. • He called the normal forward path the deferent so that it did not get confused with the epicycle. • http://videos.howstuffworks.com/hsw/20230-distance-and-time-ptolemy-video.htm

10. Major Objections to Geocentric Theory • Inaccuracy – astronomers tried MANY different values for the distances of the planets as well as their speeds to explain the was observed. • Complexity – the more they tried to change for the explanation the more confusing it became.

11. The Heliocentric Theory • The Renaissance • Fourteenth, Fifteenth, and Sixteenth centuries brought the great rebirth of learning. • Renewed interest in every area of culture: art, literature, music, drama, geography, science, and medicine. • Also, a reawakening for the Bible. • Gutenberg printing press allowed for books to be reprinted more easily.

12. The Heliocentric Theory • Sun centered as opposed to Earth centered. • The sun remains still and everything revolves around it with the exception of the Earth’s moon. • The Earth’s moon revolves around the Earth.

13. Heliocentric Scientists • Copernicus • Aquinas • Galileo • Kepler • Newton • Tycho

14. Copernicus • Polish – formulated the heliocentric theory • Born during the renaissance. • Disillusioned by the many “tricks” that must be played to get the Geocentric Theory to work. • Author of “The Six Books Concerning the Revolutions of the Heavenly Spheres” or “The Revolutions” for short. • Answered many arguments that critics tried.

15. Critics Spinning earth would fly apart Birds would be left behind If earth revolved around sun then the nearer stars would shift their position compared to distant stars when viewed from different places Answers Rotating sky more likely to fly apart because of size Earth drags along the atmosphere including birds They do indeed shift and it can be seen with a telescope Copernicus’ Arguments

16. Copernicus’ Arguments • Also addressed the issue of planets appearing to move backwards. • Proved that as the earth caught up to a slower moving planet such as Mars or Jupiter, it would appear to make the planet go backwards as the earth went by. • Heliocentric Theory is also called the Copernican Theory because of his advances.

17. Tycho Brahe • Danish nobleman • One of the most accurate astronomical observers is history. • He did not agree with Copernicus, but his observations helped to establish the Heliocentric theory as superior. • Built an observatory on the Isle of Hven near Copenhagen and studied for the next 20 years the positions of stars and planets.

19. Johannes Kepler • German astronomer, Outstanding Christian and brilliant mathematician • Joined Tycho’s staff in 1600 in Prague after protestants were persecuted and forced to leave Austria. • He recognized the brilliance of Tycho’s work. • Devised three laws that described the planetary motion.

20. Johannes Kepler • First two laws published in a book “New Astronomy” in 1609. • Third law came in 1618. • His major contribution to the Copernican theory was his mathematical proof that the orbits of the planets were actual ellipitical. • Very important that his work glorify God. • http://videos.howstuffworks.com/hsw/23314-the-history-of-astronomy-laws-of-planetary-motion-video.htm

21. Galileo • First to use a telescope for astronomy • First to observe that Venus has phases like the moon. • First to observe Saturn’s rings, but he did not identify them as rings. • Discovered the four largest moons of Jupiter. • Jupiter’s moons helped solidify the sun centered and earth rotating around it theory

22. Galileo • Galileo’s book Dialogue on the Two Chief World Systems was banned by the Catholic church. • The church had accepted the geocentric theory and centered their doctrine around it. • He was tried before the Catholic Inquisition and placed on house arrest for the rest of his life.

23. Newton • English mathematician and physicist that described the force between the sun and the celestial objects around it. • Was inspired to formulate the law of gravity by an apple falling from a tree. • Described that the more mass an object has the more force it exerts on other objects.

24. Newton • Law of Universal Gravitation – Any two bodies attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. • Gravity provides the force that holds the planets in orbit around the sun and the moons around the planets. • http://videos.howstuffworks.com/hsw/19121-exploring-gravity-the-law-of-universal-gravitation-video.htm

25. Foucault • French physicist who determined the speed of light. • Hung a pendulum in the Pantheon to prove that the earth rotates. • The swing of the pendulum changed as the earth rotated. • http://www.classzone.com/books/earth_science/terc/content/visualizations/es0403/es0403page01.cfm?chapter_no=visualization

26. Aquinas • Italian philosopher • Thought he could reconcile the natural philosophy and thinking of the ancient pagans with Christianity.

27. Chapter 2 part BEvidence That the Earth Moves • Two motions: • Rotates – spins around an imaginary line (axis) • Revolves – moves around the sun in its orbit • Both motions can be proven from observations

28. Evidence of Rotation • The sun, moon, planets, and stars rise in the east and set in the west. • Northern stars move counterclockwise in circles centered on the North Star

29. Earth’s Shape • Earth’s Shape – slightly flattened at the poles and bulging at the equator; 7928 miles around equator but 7901 miles around the poles. • Jupiter and Saturn spin the fastest and show this effect the greatest; can see through a telescope that these planets are not round.

30. Earth’s Shape • Mercury and Venus, the slowest spinning planets appear the most spherical. • Inertia – the tendency of moving matter to continue moving in the same direction. • The planet’s surface is moving fastest at the equator which explains the bulge at the equator.

31. Spinning Demo

32. Wind Patterns and Projectile Paths • Wind patterns would be much simpler if the earth did not rotate; the warm air from equator would move toward poles and cooler air from higher latitudes would move toward equator; straight north and south. • Coriolis effect – tendency for objects moving in straight path to curve • Surface of the earth moves at different speeds at different latitudes.

33. Foucault Pendulum • Understood inertia – an moving object continues moving in the same direction unless acted upon by an outside force. • At the poles the earth turns at a rate of 15° per hour, 90° per six hours, 360° in 24 hours • At the equator the you would not see the degree changes because the earth is moving with the point of attachement.

34. Direct Observation • Astronauts on the moon saw the entire surface of the earth within 24 hours. Since the moon does not revolve around the earth each day it could only mean that the earth was rotating.

35. Evidence of the Earth’s Revolution • Evidence that supports both theories includes the sun’s apparent path through the stars and the earth’s seasons.

36. Sun’s APPARENT Motion - Ecliptic • When looking at an object in front of a moving background it can appear that the object is the one moving. • The sun appears to be moving when you look at the sun with the stars in the background. • Really the stars are the objects moving; they rise approximately 4 minutes earlier each day.

37. Seasons • Why do we not experience summer when the earth is closest to the sun? • The tilt of the earth’s axis! • Three reasons why summer is warmer: • Day is longer so heat is absorbed longer • Sun rays are more concentrated; absorb more energy per square kilometer • Higher angle sun rays lose less energy to the atmosphere as the travel a shorter distance

38. Solstices and Equinoxes • Summer Solstice – June 21 – Sun is directly over the Tropic of Cancer; sun’s apparent northward motion stops; appears to move southward. • Winter Solstice – December 21 – Sun is directly over the Tropic of Capricorn; sun’s apparent southward motion stops; appears to move northward.

39. Solstices and Equinoxes • Vernal Equinox - ~March 21 – The sun is directly over the equator. • Autumnal Equinox - ~ September 22 – The Sun is directly over the equator. • These dates can fluctuate by a day because of leap year.

40. Stellar Parallax • Stellar – means stars • Parallax – the apparent shift of nearby stars among farther stars as the earth’s position around the sun changes. • Eye Demo:

41. Stellar Parallax • Wilhelm Bessel first discovered a star’s parallax in 1838. • The closer the star the less parallax is observable. The first star observed for parallax was 67 trillion miles away.

42. Meteoric Evidence • The meteors are generally brighter and more plentiful after midnight. • The observer is on the leading side of the earth as it races along its orbit, logically causing more collisions on the “front” side of the earth. • If the earth were stationary there wouldn’t be an explanation that could satisfy this observation.

43. Calendars • The first recording of a time reference was Genesis 1:5, “The evening and the morning were the first day” • Lunar – totally based on the moon’s phases (Muslims) • Lunisolar – based on both the moon’s phases and the solar year (Hebrew and Chinese) • Solar (Julian) – based only on the sun. Used for all national governments. • Gregorian – Currently used

44. Units of Time • Day – 24 hours • Week – 7 days – the most scheduling done in weekly references • Month – 30 or 31 days (exception February) • Season – 3 months – spring, summer, autumn, winter • Year – 12 months or 365 ¼ days