1. Earth’s Rotation and Revolution

2. Earth’s Rotation CAUSES DAILY CHANGES
The spinning of earth on its AXIS
AXIS tilted 23.5°

3. Earth’s Rotation Rotation west to east Counterclockwise 15°/hour
AXIS always points to Polaris

4. During Revolution - Tilt of the axis always stays the same – 23.5°

5. Evidence of Earth’s Rotation FOUCAULT’S PENDULUM
1851, Foucault’s pendulum will appear to change in a predictable way.
It would continue to swing in the original path if Earth did not rotate.

6. No force that makes pendulum rotate – must be earth that is rotating!!!
Inertia and gravity make it swing straight out and straight down in a straight arc – not twist.

8. Evidence for Rotation CORIOLIS EFFECT
Objects moving over the earth (air, water, planes, projectiles) to be deflected (curve away) from a straight line path
DUE TO EARTH’S ROTATION
Northern Hemisphere – right curve
Southern Hemisphere – left curve

13. What are the APPARENT DAILY MOTIONS of Celestial Objects?
Motion appears to make
However, the apparent motion is caused by Earth’s rotation west to east 15 ° / hour (counterclockwise)
For example, the stars appear to move from east to west. The paths are circular or parts of a circle called an arc.

14. Celestial Sphere: A huge imaginary sphere around the Earth to which the stars appear to be attached.
But in reality the celestial sphere is stationary and the earth is rotating counterclockwise
ALL MOTION 15°/HR

15. Stars in constellations are often very far from one another but we see them in the same direction in the sky.
Big Dipper

16. Stars appear to be moving from east to west. Stars rising in the east.

17. Stars appear to be moving from east to west
Stars appear to be moving from east to west. Rise in the east and set in the west.

18. Northern part of the sky around Polaris
CCW
Moving west to east

20. CIRCUMPOLAR STARS POLARIS

21. The complete circular path can be seen for stars in the northern part of the sky around Polaris
Circumpolar constellations never set.
Circumpolar constellations change with latitude

22. Earth’s Revolution Around Sun
Elliptical orbit
It takes Earth days – 1 year
It moves approximately 1° per day.

23. Evidence of Earth’s Revolution around the Sun
4 SEASONS
2. Seasonal Constellations: Visible at night only during certain seasons.
Constellations are visible when the dark side of Earth (away from sun) faces toward the constellation.

24. The 13 constellations the sun appears to travel through during the year
August, at night, you see Sagittarius and Capricornus but the sun appears by Cancer

25. Different constellations at different times of the year

26. Rotation: DAILY path of sun from sunrise to sunset has the shape of an arc moving l5° per hour.
Revolution: Sun’s arc changes position, ALTITUDE and length with the seasons

27. Winter LOWER ALTITUDE SHORTER DAYLIGHT ARC

28. SUMMER HIGHER ALTITUDE LONGER DAYLIGHT PATH

29. Summer - 90º angle of Sun’s rays at Tropic of Cancer 23.5º North
Because of the earth’s spherical shape, on any particular date, there is just 1 place where insolation (incoming solar radiation) is at an angle of 90°. All other places are less than 90°.
Does the 90° ever reach the United States?
An observer in New York State will never see the Sun directly overhead.

30. Earth’s Revolution around the Sun – the tilt of Earth’s axis does not change producing a cyclical change of seasons

31. SUMMER – NORTH POLE TILTED TOWARD SUN

32. EQUINOXES – NO TILT

33. Winter Solstice – North Pole tilted away from Sun

37. Due to 23º tilt of the Earth’s axis 90° Perpendicular Rays of the Sun aka the ZENITH POSITION travel between Tropic of Cancer and Tropic of Capricorn
June ° N
Tropic is from the Greek for "turning" describing the Sun's motion at the solstices. Solstice means “sun stops”
March/Sept. 21
Dec ° S

38. HIGHEST ALTITUDE OF SUN AT SOLAR NOON

39. Summer maximum altitude of noon sun is 73. 5°, Winter is 26
Summer maximum altitude of noon sun is 73.5°, Winter is 26.5° Spring/Autumn?
(Sun 90 at = =72.5) ( 90-41= 49) ( = = 25.5)

40. Changing Altitude of the Noon Sun
LONG ISLAND, NEW YORK

44. HOW DOES THE LOCATION OF SUNRISE AND SUNSET CHANGE DURING THE COURSE OF THE YEAR
NO MATTER WHERE YOU ARE ON THE GLOBE, ON THE EQUINOXES THE SUN WILL ALWAYS RISE DUE EAST AND DUE WEST
WHEN THE SUN TRAVELS NORTH OF THE EQUATOR TO THE TROPIC OF CANCER ON JUNE 21ST (23.5°N), THE SUNRISE AND SUNSET POSITIONS WILL MOVE NORTH OF EAST.
WHEN THE SUN TRAVELS SOUTH OF THE EQUATOR ° TO THE TROPIC OF CAPRICORN ON DECEMBER 21ST (23.5°S), THE SUNRISE AND SUNSET POSITIONS WILL MOVE SOUTH OF EAST

45. EQUINOXES – DUE EAST

46. SUMMER SOLSTICE NORTH OF EAST

47. WINTER SOLSTICE SOUTH OF EAST

48. The apparent rising and setting of the sun is due to rotation Changes in the altitude of the path and horizon position of sunrise and sunset are due to revolution
Season
Sunrise
Sunset
Summer
North of east
North of west
Equinox
Fall/Spring
Due east
Due West
Winter
South of east
South of west

49. “ALASKA MIDNIGHT SUN” NORTHERN HEMISPHERE FROM MARCH 21 UNTIL SEPTEMBER 21 – SUN DOES NOT SET TIMED PHOTOGRAPHY

50. The tilt of the Earth on its axis is also responsible for the day and night length:
What date is it here?
What date is it here?
June 21st
December 21st

53. EQUINOX (MEANS EQUAL NIGHTS)
12 HOURS OF DAYLIGHT AND 12 HOURS OF NIGHT

58. Summary Rotation: Earth rotates l5° per hour in 24 hours.
Revolution: Earth takes days to revolve around the sun moving approximately 1° per day.

59. Kepler’s Three Empirical Laws of Planetary Motion
1. The orbital paths of the planets are elliptical, with the Sun at one focus

60. SHAPE OF ELLIPSES Eccentricity = 0 circle Eccentricity = 0.5
Eccentricity = line

61. TO THE HUMAN EYE, MOST ORBITS OF PLANETS LOOK LIKE CIRCLES
SLIGHTLY ELLIPTICAL SHAPE OF EARTH’S ORBIT CAUSES THE PLANET TO VARY THE DISTANCE TO THE SUN DURING REVOLUTION
147 million kms.
152 million kms.

62. Gravitational Effects of Varying the Distance to the Sun
Gravitation force influenced
by mass and distance
Greater the mass = greater the gravitational attraction
Closer the 2 objects = greater the gravitational attraction
Perihelion = greater gravitational attraction
Aphelion = less gravitational attraction

63. If gravitational attraction varies, velocity will vary
Mass stays the same but distance varies causing gravitational attraction to vary
If gravitational attraction varies, velocity will vary
Perihelion = faster velocity Aphelion = slower velocity

64. Relationship of Aphelion and Perihelion to Orbital Velocity

65. Appearance of Sun Changes with Varying Distance

67. Kepler’s Three Empirical Laws of Planetary Motion
2. An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time..
Area 1
Area 2

69. Velocity is NOT CONSTANT
This is the best website for 1st and 2nd laws of Kepler

71. Evidence of Revolution Parallax Shift
Because of Earth’s revolution about the sun, near stars seem to shift their position against the farther stars (closer star – greater the shift)
If you observe the same star while earth is at 2 different points during its orbit around the sun, the star’s position relative to the more distant background stars will appear to change.

74. Parallax Shift