Earth_Motion_Notes

1. EARTH MOTIONS
TOPIC 3

2. TRUE
MOTIONS
“Real Motions”
Rotation
Revolution
APPARENT
MOTIONS
“What appears to
move”
Sun
Stars
Moon
Planets

3. ROTATION:
• The spinning of Earth on its axis.
• Earth rotates from West to East
(counterclockwise when viewed from the
North Pole).
• 24 hours (15o/hour)
Drawing
*!* The Earths axis is tilted 23.5o relative to
the sun.

4. REVOLUTION:
• The orbiting of Earth around the sun.
• 365.26 days (1 o /day)
Drawing

5. APPARENT MOTION OF THE
STARS
Daily Motions
• Stars appear to move
in circular paths
around Polaris at a
rate of 15 o/hour.
• Eastward to
westward.
• Due to rotation.
Ex:
Annual Motion
• Some constellation
are seasonal while
others can be seen
year round.
• Circumpolar vs. non-
circumpolar.
• Due to revolution.

12. Apparent Motion of the Sun
• The Sun appears to move from east to west at a
rate of 15 o/hour.
• The path of the sun changes with the seasons
and with latitude.
• Local solar noon- occurs when the sun reaches
its highest point in the sky.
• Only between 23.5 N and 23.5 S will the sun
ever be directly overhead! (the tropics)
• The sun is NEVER overhead for an observer in
the continental U.S.
• See sun’s path diagram

17. True Motions of the Moon
• The Moon revolves around Earth and
rotates on its axis once every 27 1/3
days.
The revolution of the Moon is responsible
for…..
1. The phases of the Moon.
2. Tides
3. Eclipses

18. MOON PHASES
• The varying amounts of the lighted moon
as seen from Earth.
• The period from one full moon to the next
is 29 ½ days.
• http://www.astro.wisc.edu/~dolan/java/Mo
onPhase.html

25. TIDES
• The cyclic rise and fall of ocean waters
due to the gravitation between the Earth,
moon and sun.

30. SPRING vs. NEAP TIDES
SPRING TIDES
Higher high tides, lower low tides.

31. NEAP TIDES:
Lower high tides higher low tides.

37. ECLIPSES:
LUNAR SOLAR

48. MODELS OF THE UNIVERSE
• GEOCENTRIC
• Ptolemy
• “Earth Centered”
• Drawing:
• HELIOCENTRIC
• Copernicus
• “Sun Centered”
• Drawing:

50. Best Evidence of the Earths
Rotation…
1. Foucault Pendulum
2. Coriolis Effect- the apparent deflection
of the path of a moving object due to the
rotation of Earth.
• N. Hemisphere – to the right
• S. Hemisphere - to the left

51. ORBITAL GEOMETRY
Keplers 1st Law
 Planets orbit the sun in slightly eccentric
elliptical paths with the sun at one of the
foci.

52. Johannes Kepler

53. • http--home.cvc.org-science-kepler.gif

54. http://home.cvc.org/science/kepler.
gif
http--home.cvc.org-science-kepler.gif
http://home.cvc.org/science/kepler.gif

55. Eccentricity:
• “ out of roundness”
• Formula:
eccentricity = distance between foci
length of major axis
• All eccentricity values must be between 0
and 1 (decimal)!

57. Kepler’s 2nd Law
• A line drawn from a planet to the sun will
sweep across equal areas in an equal
amount of time.
What does this tell us?
• The closer a planet is to the sun, the
greater its orbital velocity (speed).

58. Kepler’s 3rd Law
• The period of a planet squared is equal to
its distance from the sun cubed. (P2=D3)
What does this tell us?
• Planets that are further away from the sun
take longer to revolve.

59. Perihelion
• The point in a planets orbit when it is
closest to the Sun.
• Around Jan 4th
Aphelion
• The point in a planets orbit when it is
furthest from the Sun.
• Around July 4th