1. Part 2 – Motions of Earth, Moon, and Sun
Astr nomy
Part 2 – Motions of Earth, Moon, and Sun

2. Models of Apparent Motion
Remember, apparent motions of celestial objects mean these objects appear to move, but really, it’s Earth that is moving.
There have been 2 main models to explain these apparent motions.
1. Geocentric Model
2. Heliocentric Model

3. Models of Apparent Motion
Geocentric Model:
Early cultures believed this one.
It says the Earth is the center of everything and all objects move around it.
Geo = Earth
Yeah Right!

4. Models of Apparent Motion
Heliocentric Model:
Model that is used and believed today.
It says the sun is the center of our solar system and everything moves around it.
Helio = sun

5. Animations of Geocentric vs Helicentric

6. Foulcault Pendulmn Houston Museum of Natural Science
Earth's Motions
We know that the Earth rotates.
However, HOW do we know this for sure?
1. The Foucault Pendulum
The path of the pendulum changes in a predictable way throughout the day.
Foulcault Pendulmn animation link
Foulcault Pendulmn Houston Museum of Natural Science

7. 2. The Coriolis Effect
All particles on Earth, including wind, are deflected or curved from their original path.
Merry go round movie clip
Coriolis Effect video
Coriolis Effect makes the movies
Coriolis Effect on Toilet in Southern Hemisphere
Snopes Explanation

8. Regents Question
A Foucault pendulum appears to change its direction of swing due to the
(1) tilt of Earth’s axis
(2) spin of Earth on its axis
(3) deflection of Earth’s planetary winds
(4) movement of Earth in its orbit around the Sun
Answer is… 2

9. Regents Question The best evidence that Earth rotates is provided by
(1) The location of mid-oceanic ridge volcanoes and the distribution of index fossils
(2) The movement of Foucault pendulums and the Coriolis effect on air movement
(3) The pattern of changing seasons and the depth of meteor impacts
(4) The rate of uranium-238 decay and changes in atmospheric composition
Answer is… 2

10. The Motions of the Moon
Revolution – Counter clockwise, 1 revolution takes 27 1/3 days.
Rotation - Counter clockwise, 1 rotation takes 27 1/3 days.
Always see the same side of the moon.
Phases of Moon- 29½ days long.

11. The Motions of the Moon
Why are there an extra 2 1/6 days?
Moon has to revolve for 2 more days to get back to the new moon phase.
This occurs because the Earth is revolving around the Sun.

12. Caused by the positions of the Earth, Moon, and sun.
They repeat because the moon orbits the Earth.

13. New Moon
Waxing Crescent
First Quarter
Waxing Gibbous
Full Moon
Waning Gibbous
Last Quarter
Waning Crescent

14. New Moon
Waxing Crescent

15. First Quarter
Waxing Gibbous

16. Full Moon
Waning Gibbous

17. Last Quarter
Waning Cresent

19. Regents Question
One complete cycle of the phases of the Moon takes approximately one
(1) day
(2) month
(3) Week
(4) Year
Answer is… 2

20. Lunar Eclipse Time Lapse
Eclipses
2 types of eclipses:
1. Lunar eclipse – eclipse of the moon.
Earth casts a shadow on the moon during the FULL MOON phase.
Lunar Eclipse
Lunar Eclipse Time Lapse

24. Eclipses 2. Solar Eclipse: Can only happen during a NEW MOON phase.
See A Solar Eclipse
2. Solar Eclipse:
Can only happen during a NEW MOON phase.
In rare cases the moon in this phase can block out the sun, casting a shadow onto Earth, which causes a solar eclipse.

25. Why don’t we have Solar and Lunar eclipses every month?

26. Eclipses

27. Partial Solar Eclipse
Total Solar Eclipse

28. World Map of Future Eclipses

29. Regents Question The passage of the Moon into Earth’s shadow causes a
(1) lunar eclipse
(2) new Moon
(3) solar eclipse
(4) full Moon
Answer is… 1

30. Tides

31. Tides Bay of Fundy Time Lapse Crazy Tides… Tidal Bore China
Reversing Falls

32. Tides
The gravitation between the Earth, Moon, and Sun results in a cyclic rise and fall of ocean waters on Earth.
These are called tides.
A bulge of water is a high tide and occurs when the gravitational pull of the moon is the greatest.
This will occur on the side facing the moon, and on the exact opposite side.

33. Tides On the other 2 sides, there will be a low tide.
This is where the gravitational pull of the moon is the least.

36. Tides
Spring Tide – every new and full moon phase the Sun, Earth, and Moon are in a straight line.
This causes even higher high tides.
Neap Tide – During the first and third quarter moon phases, the Sun, Earth, and Moon are at a right angle to each other.
This causes the smallest difference between high and low tides.

37. During which phases of the moon
do neap and spring
tides occur?

38. 1st & 3rd Quarters
Neap?

39. New or Full Moon
Spring?

40. How many tides a day?
2 high tides
2 low tides

41. Why are there not exactly
12 hours between tides?
because the moon
revolves around
the Earth while the
Earth rotates

42. Regents Question
The cyclic rise and fall of ocean tides on Earth is primarily caused by Earth’s rotation and the
(1) temperature differences in ocean currents
(2) revolution of Earth around the Sun
(3) direction of Earth’s planetary winds
(4) gravitational attraction of the Moon and the
Sun
Answer is… 4

43. Tide and Gravity animation

44. High Tide or Low Tide