1. Ancient Astronomy and the Celestial Sphere

2. What do we see in the sky? Daily apparent motion of sky overhead
Motion of Sun, Moon and planets against stars
Seasonal change of Sun’s path
Different stars appear in the evening at different times in the year

3. Some astronomical terms
Celestial sphere
North and South Celestial Poles
Celestial Equator
Ecliptic
Direct Motion (eastward on ecliptic)
Retrograde Motion (westward on ecliptic)

4. Celestial Sphere

5. Celestial Coordinates

6. The Ecliptic and the Celestial Equator

8. Declination and Right Ascension

9. Ecliptic
The Sun’s apparent path through the sky over one year, through the constellations of the zodiac.
At an angle of 23½0 to the celestial equator.
Summer solstice: June 21
Winter solstice: December 21
Vernal equinox: March 21
Autumnal equinox: September 21

10. Ecliptic

12. Eclipses Lunar eclipses. Solar eclipses. Annular solar eclipses.
Eclipse tracks.

13. Solar Eclipse

14. Solar Eclipse

15. “Diamond Ring” Effect

16. The Umbra of a Solar Eclipse

17. Solar Eclipse Paths

18. Annular Solar Eclipse

19. Lunar Eclipse

20. Lunar Eclipse- Curved Shadow of the Earth

21. Aristotle Born 384 BC (lived in Athens and Macedonia). Died 322 BC.
Student of Plato.
Lectured and wrote extensively on logic, rhetoric, poetry, ethics, economics, politics, physics, natural history, anatomy, physiology.
Compared to Plato, relatively devoted to the study of the world.

22. The Nature of the World
The world is composed of four elements: Earth, Water, Air and Fire, in order of lightness.
Everything seeks its natural level.
The heavens are made of quintessence.
Everything in the heavens is spherical, and moves in a circular path around the Earth.

23. Impetus
A property transmitted to an object by a mover (e.g. a throwing arm). In most medieval concepts, this property is “used up” as the object moves.

24. Ptolemy Lived in Alexandria c.140 AD. Observed the stars and planets.
Attempted to fit the motions of the planets into a Geocentric system using circular motion.

27. Retrograde Motion: Jupiter and Saturn June 2000-May 2001
©Tunc Tezel, 2001

28. The Ptolemaic System
To match observed planetary motion, Ptolemy needed
Deferent
Epicycle
Equant

31. Heliocentric Solar System of Aristarchus

32. Counterarguments to Heliocentric System
No parallax observed.
No periodic brightening of stars as Earth approaches and recedes.
No sense of motion.
No physical context for heliocentric theory.

33. Nicholas Copernicus Born 1473 (in Torun, Poland). Died 1543.
Proposed heliocentric system, with planets moving in circular orbits.
Author of De Revolutionibus (On the Revolutions).

34. Copernican System Planets move around the Sun in circular orbits.
The Earth (and Moon) are third from the Sun.
Simple explanation of retrograde motion.

35. Copernican Explanation of Retrograde Motion
                                                                                           

36. Tycho Brahe Born 1546 (in Denmark). Died 1601.
Made extensive observations of the motions of the planets.
Observed the supernova of 1572 and reasoned that the stars cannot be unchangeable.

37. Johannes Kepler Born 1571 (near Stuttgart, Germany). Died 1630.
Assistant to Tycho Brahe.
Originated three laws of planetary motion.
Realized that planetary orbits must be ellipses.

38. Kepler’s First Law
Planets move in ellipses, with the Sun at one focus.

39. How to Draw an Ellipse

40. Keplerian Orbital Parameters
Semimajor axis: a (AU).
Eccentricity: e = c/a.
Sidereal Period: P (years).
Inclination: angle to ecliptic plane ( 0 ).

41. Kepler’s Second Law
The radius line from the Sun to a planet sweeps out equal areas in equal times.

42. Kepler’s Third Law
The square of the sidereal period is equal to the cube of the semimajor axis, or
P2 = a3

43. Galileo Galilei Born 1564 (in Pisa, Italy). Died 1642.
First to use a telescope for astronomical observations.
Author of Dialogue Concerning the Two Chief World Systems.
Originated concept of Galilean relativity.

44. Galileo’s Telescope Observations
The phases of Venus.
Mountains and craters on the Moon.
Sunspots.
The four bright satellites of Jupiter.
The rings of Saturn.
Neptune (although Galileo did not realize it was a planet).

45. Galileo’s Observations of Venus

46. Mountain and craters on the Moon

47. The satellites of Jupiter

48. Sunspots

49. Galileo’s Heresies
Falling bodies move at the same speed, regardless of mass.
The 1604 Supernova must be a star.
Letter to Christina of Lorraine (1615)
Dialogue Concerning the Two Chief World Systems (1632)

50. Isaac Newton Born 1642 (in Lincolnshire, England). Died 1727.
Originated Three Laws of Motion
Originated Law of Universal Gravitation.
With Leibniz, invented Calculus.
Author of the Principia.
Invented the first reflecting telescope.

51. Mass and weight
Mass is the amount of matter in an object. We measure it in kilograms (kg).
Weight is the force exerted by gravity on an object. We measure it in newtons (N).

52. Your weight on various planets
Planet Weight (lbs)
Mercury 57
Venus
Earth
Moon 26
Mars 57
Jupiter
Saturn
Uranus
Neptune
Pluto 14

53. Newton’s First Law of Motion
An object at rest tends to remain at rest. An object in motion moves at a constant speed in a straight line unless acted upon by a force.

54. Newtonian Orbits
Illustration from Pricipia, VII, Book 3, p. 551

55. Newton’s Second Law of Motion
The acceleration of an object is directly proportional to the force acting on it and inversely proportional to its mass.
Force = mass × acceleration
F = m a

56. Newton’s Third Law of Motion
For every action there is an equal and opposite reaction.

57. Law of Universal Gravitation
The gravitational force between any two objects is proportional to the product of their masses and inversely proportional to the distance between them.
binary star java applet

58. Expanding our Solar System
Uranus: discovered by William Herschel (1781).

59. Expanding our Solar System
Neptune: position predicted by Adams and Leverrier; discovered by Galle (1846).

60. Expanding our Solar System
Pluto: discovered by Clyde Tombaugh (1930).