1. Earth’s Motions
Unit 4

2. ROTATION
SPIN
DAILY

3. I. Rotation
1. The earth spins on an
axis
The axis of rotation is an
imaginary line through the earth from north to south pole

4. The earth rotates around this axis
The axis is tilted
23½º from vertical

5. The axis always points towards
Polaris
This is called
Parallelism of the axis.

6. A. Results of Rotation
Sunrise and set
Moonrise and set
Planet rise and set
Coriolis effect
Motion of the foucault pendulum
Circumpolar motion of stars

7. Location of sunrise/set
is due to the direction of rotation…
the earth rotates from
west to east or
counterclockwise

8. B. Rate of Rotation
Angular rate:
360º
24 hours
15º/hr

9. Velocity is dependent upon latitude
As latitude increases
velocity decreases

10. Latitude Equator 40,080 km 1670 km/hr 42º 31,200 km 1300 km/hr 60º
Rate of
Rotation
Latitude
Circumference
Equator
40,080 km
1670 km/hr
42º
31,200 km
1300 km/hr
60º
20,140 km
839 km/hr
90º
0 km
0 km/hr

11. C. Time, the Sun and Earth’s Rotation
We use the apparent motion of the sun to tell time.
Time is based upon the actual movement of the earth

12. The earth’s rotation causes the apparent rise and set of the sun

13. The apparent path of the sun is an arc
Local solar noon is always the time at which the sun reaches its highest point in its arc
Solar noon in NYS is
never directly overhead!!

14. Z

15. REVOLUTION
ORBIT
YEARLY

16. II. Revolution
The earth travels around the sun
The orbit of the earth is
an ellipse with
the sun at one of the foci
3. The direction of revolution is counterclockwise

17. A. Results of Revolution
Seasons
Seasonal changes in visible constellations
Parallax
Retrograde motion

18. B. Rate of Revolution
Angular rate:
360º
days
~1º/day

19. Velocity
radius of revolution is 1.5 x 108
therefore
v=2(pi)r T
v = ~ 2,580,822 km/day
( mi/day)

20. Comparative velocity:
The Earth travels fastest when we are closest to the sun and
slowest when we are farthest from the sun

21. III. Seasons in the Northern Hemisphere
Seasons and seasonal changes are due to
the revolution of the earth combined with
the tilt of the earth on its axis
and parallelism of the axis

23. A. Summer Summer solstice June 21st
Northern hemisphere is tipped towards the sun
Earth is at its greatest distance from the sun (aphelion)
Altitude of solar noon is highest

24. Days are longest
Shadows are shortest
The sun appears smallest
Sunrise occurs north of east
Sunset occurs north of west

25. The zenith sun is found at 23½ºN…Tropic of Cancer
The north pole experiences 24 hours of daylight
The south pole experiences 24 hours of darkness

27. B. Fall
Autumnal equinox
September 23rd
Neither hemisphere is tilted towards the sun
The distance to the sun is decreasing

28. The altitude of solar noon is decreasing
The length of day is decreasing
Shadow length is increasing
The sun is looking bigger

29. Sunrise occurs due east
Sunset occurs due west
Zenith sun is found at the equator…0º
We experience 12 hours of daylight and 12 hours of darkness

31. C. Winter
Winter solstice
December 21st
The northern hemisphere is tilted away from the sun
The earth is closest to the sun
The altitude of solar noon is lowest

32. The length of day is shortest
Shadow length is longest
The sun appears biggest
Sunrise occurs south of east
Sunset occurs south of west

33. 11. The zenith sun is found at the Tropic of Capricorn…23½ºS
The north pole experiences 24 hours of darkness
The south pole experiences 24 hours of daylight

36. D. Spring
Vernal equinox
March 21st
Neither hemisphere is tilted towards the sun
The distance to the sun is increasing

37. The altitude of solar noon is increasing
The length of day is increasing
Shadow length is decreasing
The sun is looking smaller

38. Sunrise occurs due east
Sunset occurs due west
The zenith sun is found at the equator…0º
We experience 12 hours of daylight and 12 hours of darkness

40. Shadows in the northern hemisphere
A shadow cast
by an object at solar noon in NYS will
always point
north

41. June
July
May
Aug Ap
Sept
Mar
Oct
Feb
Nov
Jan
Dec

42. S O A N J J D J M F A M

43. D
S/M J

44. IV. The Moon Movements Revolution The moon travels a path that
is an ellipse with
the earth at one of the foci
(the other foci is called the barycenter)

45. Its period of revolution is
27 1/3 days and is called a
sidereal month
The moon’s period of rotation is
27 1/3 days …
its rotation is synchronous with its revolution

46. Because of this synchronicity, the same side of the moon always faces the earth.
Until we began exploring space, the far side of the moon remained unobserved.

47. B. Lunar Phenomena
Phases of the moon:
the changing shape of the visible moon due to the revolution of the moon around the earth

48. Because the earth is revolving around the sun as the moon revolves around the earth, one complete cycle of phases takes longer than one complete revolution
One cycle of phases takes
29½ days and is called a
synodic month

49. waning waxing SUN ¾ or gibbous quarter crescent Full moon New moon

51. Waxing…
when the visible portion of the moon is becoming larger
Waning…
when the visible portion of the moon is becoming smaller

52. Eclipses
a. Terms:
i. Umbra:
The darkest part of the shadow cast by the earth or the moon. The surface is completely blocked from view.

53. ii. Penumbra:
The area of partial shadow surrounding the darkest part of the shadow cast by the earth or the moon. The surface is only partially blocked from view.

54. b. Lunar eclipse:
when the moon is in the shadow of the earth
The moon must be in the full moon phase:
S – E – M

57. c. Solar eclipse:
when the earth is in the shadow of the moon
The moon must be in the new moon phase:
S – M – E

60. d. We don’t experience eclipses with every new and full moon because the plane of the moon’s orbit is tilted 5º to the plane of the earth’s orbit

61. When the moon is at perigee and the sun is at aphelion, the surface of the sun is completely “blocked”
When the moon is at apogee and the sun is at perihelion, we see an annular eclipse in which the sun is seen as a ring around the moon’s shadow

63. 3. Tides
The cyclic rise and fall of ocean water on the earth.
They are caused by the gravitational attraction between the moon and the earth’s waters…and, to a lesser degree, the sun and the earth

65. Tidal events occur every
6 hours
The position of the moon affects the degree of the tides

66. S – E – M = Full Moon or
S – M – E = New Moon
the sun and the moon work “together” to create extreme tides…Spring tides
very high, high tides and
very low, low tides

67. M b. S E or S E M Quarter Moon
The sun and the moon work against each other to create minimal tides

68. These tides are called
neap tides
very low, high tides and
very high, low tides

69. Without the moon, the earth would still experience tides, but certainly not to the extent that we do with the moon’s influence.

71. 4. Moonrise and Moonset
Caused by the
rotation of the earth
Occurs 50 minutes later each day because of the revolution of the moon

72. The end