1. Question of the Day What is the Shape of Earth’s Orbit?
New Sub-unit: Motions of Earth, Moon, Sun
Question of the Day What is the Shape of Earth’s Orbit?
“Mean distance from Earth to sun is mil. km.” Inference about shape of Earth’s orbit? 52

3. Planetary Orbits
Not circular
Slightly Elliptical (oval)

4. Ellipse: Oval shape
Foci: “Centers”
Focal Distance: (D) Distance between foci
Major Axis: (L) Line intersects foci

6. Eccentricity
Degree of flattening or “ovalness”
How far from circle

7. Eccentricity = D (distance between foci) L (length of major axis)

8. Eccentricity Value Range from 0  1 Line = 1 Circle = 0

10. Is the sun really the center of our solar system?
Question of the Day
Is the sun really the center of our solar system?
How could we make this more elliptical?
Increase distance between foci, and ellipse will become more eccentric. 53

11. Orbits Orbital Path: Planet around sun Perihelion: Closest to sun
Aphelion – Farthest from sun (“Away”)

12. Earth’s perihelion: 147,000,000 km
Earth’s aphelion: 152,000,000 km
Perihelion - January!
Aphelion - July!

13. Sun is NOT center of Earth’s Orbit. It’s 1 of 2 foci
Sun is NOT center of Earth’s Orbit. It’s 1 of 2 foci. Other focus is “ghost.”

15. What is shape of Earth’s orbit?
Slightly eccentric ellipse.
What does Earth’s orbit look like on this scale?
A circle

17. Why is Earth’s orbit like a “curveball,” not a “fastball”?
Question of the Day
Why is Earth’s orbit like a “curveball,” not a “fastball”?
Warm-Up
Perihelion = ?
Aphelion = ?
Revolution = ?
Rotation = ? 55

18. Why is Earth’s orbit like a “curveball,” not a “fastball”?
Question of the Day
Why is Earth’s orbit like a “curveball,” not a “fastball”?
Warm-Up
Perihelion = Closest to sun
Aphelion = Farthest (AWAY) from sun
Rotation = Spin on axis
Revolution = Orbit around sun

20. Inertia vs. Gravitation
Inertia - object at rest stays at rest, & object in motion stays in motion, unless an opposing force.
Gravitation - attractive force that exists between any 2 objects.
Greater mass = greater attraction
Closer objects = greater attraction

21. Orbit is dynamic equilibrium between inertia vs. gravity

22. Johannes Kepler (1571 – 1630) German mathematician
Discovered Laws of Planetary Motion

23. 1st Law
All planets orbit in an ______ (oval) w/ Sun at 1 focus

24. 1st Law
All planets orbit in an ellipse (oval) w/ Sun at 1 focus

25. Planetary orbits are close to circular

26. Comets are most eccentric
Ex. Halley’s Comet e = .967

27. 2nd Law Planet’s speed (orbital velocity) changes as it orbits Sun
Fastest when Near Sun

28. Equal areas swept out in equal time periods

29. Areas in red are equal.
Time required for planet to travel from A to B is 21 days. How long will it take to travel from C to D?

30. 3rd Law
Farther from Sun, the longer or shorter the time for 1 orbit?

31. Farther from Sun, the the time for 1 orbit?

32. 3rd Law Farther from Sun, the longer the time for 1 orbit
1. Outer (Jovian) Planets Slower
2. Inner (Terrestrial) Planets Faster

33. Gravity
M1 M2 D2
M = Mass
D = Distance between centers of gravity of two objects
Direct or Indirect?
1) Gravity vs. Mass
2) Gravity vs. Distance

35. Question of the Day Do stars really move?
Match:
1) Revolution
2) Rotation
3) Spin on axis
4) Orbit A B 56

36. 1st Law
All planets orbit in an (oval) w/ the Sun at 1 focus (center point)

37. 2nd Law
A planet’s orbital speed is fastest when it is _________ the Sun

38. 3rd Law
The farther a planet is from the Sun, the the period for 1 orbit

39. 1. Apparent Motion of Stars
Stars are stationary!!!
Appear to move across sky

41. Star Trail (Eastern Horizon)

42. Star Trail (Western Horizon)

43. Star Trail (Northern Horizon)

44. A. Daily motion
Caused by Earth’s rotation
15º / hr.
Counterclockwise

46. B. Seasonal Changes Constellations visible different times of year
Caused by Earth’s revolution
Ex. Orion  autumn/winter

49. 2. Apparent Motion of Planets
Same daily motion as stars - Earth’s Rotation
Retrograde (backward) motion - Earth’s Revolution

50. Retrograde Motion
Earth – green Mars – red Sun – yellow

51. 3. Apparent Motion of Moon
E to W daily - Earth’s rotation
Rises 50 minutes later each day - moon’s orbit around Earth

53. 4. Apparent Motion of Sun A. Daily Motion – Earth’s rotation
Arc-shaped path
E to W
15º / hr.

55. B. Yearly Motion of Sun Due to Earth’s revolution
Altitude above horizon changes - due to Earth’s tilt

57. Geocentric Model Earth-centered Earth is stationary
Sun & Planets orbit Earth
Could not explain retrograde motion

58. Heliocentric Model
Sun-centered
Earth rotates on axis
Earth orbits Sun

61. Question of the Day How do we know Earth rotates & revolves?
What is X? What is Y?
Heliocentric Geocentric X Y 57

62. Earth’s Rotation
360° counterclockwise - 24 hrs. (day)
15° / hr.
Axis - imaginary line from N. Pole to S. Pole
Axis tilted 23.5°

63. Evidence of Earth’s Rotation
1. Foucault Pendulum Freely swinging pendulum whose path appears to change.

65. 2. Coriolis Effect Deflection of moving particles (ex
2. Coriolis Effect Deflection of moving particles (ex., wind) to right in N. Hemisphere

66. 3. Day & Night (sunrise, sunset)
The prime meridian
SUNLIGHT
A time meridian
A standard time zone is 15° wide.

67. Earth’s Revolution
Elliptical orbit with sun as 1 of 2 foci
Counterclockwise
1 revolution = days (1 year)

68. Evidence of Earth’s Revolution
1. Changing Seasons

69. 2. Changing Length of Day

70. Evidence of Earth’s Revolution
3. Changing Constellations

72. Question of the Day What’s are the reasons for the seasons?
1. Summer solstice ___
2. Winter solstice ___
3. Vernal & autumnal equinoxes ___
A) Day & night are equal
B) Sun - longest path, highest in sky
C) Sun - shortest path, lowest in sky 58

73. Most Important Point!
Earth’s tilt & orientation stay the same as it orbits Sun
Axis always points to Polaris

74. Reasons for the Seasons? Earth’s Tilt & Revolution
SUN

77. Tropics

78. Tropic of Cancer (23.5º N) Tropic of Capricorn (23.5º S)

79. Summer Solstice (June 21)
Direct sun over Tropic of Cancer
Longest day (in N. Hemisphere)

80. Summer Solstice
Sun at highest altitude
Sunrise/set NORTH of Due East-West

81. Winter Solstice (December 21)
Direct sun over Tropic of Capricorn
Shortest day

82. Winter Solstice
Sun at lowest altitude
Sunrise/set SOUTH of due East-West

83. Vernal Equinox (March 21) & Autumnal Equinox (Sept. 21)
Direct sun over Equator (0º)
Equal day and night everywhere

84. Vernal (Spring) & Autumnal Equinoxes
Sun at middle altitude
Sunrise/Sunset due East-West

89. Question of the Day Why does the sun’s path change with the seasons?
1. In which horizon are these star trails possible: N, S, E, W?
2. What star is at center?
3. Rotation or Revolution? 59

92. Daily Motion of the Sun Due to Earth’s _______
Moves in an ___-shaped path
East to West or West to East direction?
Rate = ___ degrees/hr

93. Seasonal Motions of the Sun
Caused by Earth’s _____________ around the _____ .

94. 1. Changes in Sun’s Altitude (angle above horizon)
Increases Dec. 21 (Winter Solstice) to June 21 (Summer Solstice)
Decreases June 21  Dec. 21

95. Solar Noon Local time when sun reaches highest point that day

98. Earth’s Revolution

99. 2. Location of Sunrise/Sunset
March 21 (vernal equinox) & Sept. 21 (autumnal equinox), sunrise/set = due east to due west
March 21  Sept 21, sunrise/set more north
Sept 21  March 21, sunrise/set more south

100. Sun is never directly overhead at 90º altitude (zenith) except in tropics!

101. Earth’s Revolution

102. 3. Changes in Path Length As altitude increases, path length ________
_________ relationship with length of day.

103. Earth’s Revolution

106. Question of the Day What factors affect apparent path of sun?
1) Which shows summer solstice, winter solstice, equinoxes: A, B, C?
2) Which shows longest day, shortest day, same day as night? B C 60

107. Celestial Sphere
Imaginary sphere on which all celestial objects appear

108. Altitude # degrees above horizon Vertical measurement
0 degrees = horizon (Reference Pt.)
90 degrees = zenith or overhead

109. Azimuth # degrees from due north Horizontal North = 0º (Reference Pt.)
East = 90º
South = 180º
West = 270º

111. What is reference point for altitude?
What is reference point for azimuth?