1. The Sun-Earth-Moon System

2. Earth and the Universe
Long ago people carefully studied the positions of the sun, moon, and Earth
Although they made many accurate observations, they believed Earth was the center of our solar system

3. The Sun
Objects in the solar system orbit the Sun because it contains more than 99% of the solar system’s mass
It has a HUGE gravitational pull and is the biggest object in our solar system

4. Motions of Earth Earth is always moving! The Earth is rotating as
well as revolving in space.
The Earth is so large that you don’t notice!

5. Earth’s Orbit
As you read this Earth is moving around the Sun because the sun has a huge gravitational pull
(because it is huge!)
Without the Sun’s pull, Earth would move off into space in a straight line
(because nothing would be controlling it’s path)

6. Earth’s Orbit
Earth’s orbit around the Sun is nearly round, or elliptical
The orbit of an object around another object is a revolution
It takes Earth days, or one year to revolve around the sun

7. Earth’s Distance From The Sun
The distance between Earth and the Sun is NOT always the same
An astronomical unit (AU) is the average distance between Earth and the Sun

8. Earth’s Distance From The Sun
AU = 150 million km
Scientists often use AUs to measure distances to planets and other objects within the solar system

9. Earth’s Rotation The imaginary rod through Earth is called an axis.
Earth spins on its axis like a top
Rotation is the spin of an object around its axis

10. Earth’s Rotation Rotation is what causes day and night
The side of Earth facing the sun is in daylight
Earth makes 1 rotation every 24 hours

11. Earth’s Tilt and Seasons
Seasons occur because Earth’s tilt does not change as Earth orbits the Sun

13. Equinox
An equinox occurs when Earth’s rotation axis is tilted neither toward nor away from the sun
Daylight and nighttime hours are equal on these days
There is an equinox in March and September

15. Solstice
When Earth’s rotation axis is tilted directly toward or away from the sun a solstice occurs.
Solstices happen in June and December.
These are days of the shortest (December) and longest (June) hours of daylight a year

17. The Moon

18. Gravity GRAVITY! What force keeps the Moon in orbit around the Earth?
It is the same force that holds Earth in orbit around the Sun.
GRAVITY!

19. Moon Facts A quarter (1/4) the size of Earth
The craters on the moon were caused by asteroids and comets that crashed into it over time.

20. Formation of the Moon Scientists believe the Moon
formed when an object the size
of Mars collided with Earth
when Earth was very young
This collision made a lot of pieces of Earth fall off
Eventually, gravity pulled these pieces together – forming the moon

21. Motions of the Moon The moon rotates on its axis
The moon revolves around Earth
The Moon completes an orbit around the Earth every 27.3 days

22. So Why Do We Always See The Same Side of the Moon?
Because the moon revolves
and rotates in the same amount of time, the same side of the moon always faces Earth
The side of the moon that doesn’t face Earth is the far side of the Moon.

24. The Moon’s Rotation

25. The Moon DOES NOT Create Its Own Light!

26. Phases of the Moon The Moon is visible because
it is reflecting light from the sun
The Moon completes all phases after 29.5 days

28. Phase: New Moon When the Moon is between Earth and the Sun, the sunlit
half of the Moon faces away from Earth
The half facing Earth is dark because it is in shadow

30. Waxing
During the 2 weeks after the new moon more of the moon becomes visible.
As the lit portion of the Moon becomes larger, the Moon is waxing
Waxing Phases:
Waxing crescent
First quarter
Waxing gibbous

32. Full Moon
When Earth is between the Moon and sun, the sunlit half of the Moon faces Earth
This is a full moon!

34. Waning
During the 2 weeks after a full moon, the less sunlit side of the Moon is visible
As the lit portion of the Moon becomes smaller, the Moon is waning
Waning Phases:
Waning gibbous
Last Quarter
Waning Crescent

36. Tides

37. Tides
Tides are the periodic rise and fall of the oceans’ surfaces caused by the gravitational force between Earth and the Moon and Sun

38. Tides and the Moon
The Moon has much more influence on the tides because it is much closer to Earth than the Sun.

39. Effect of the Moon
Locations on Earth closest to and farthest from the Moon undergo the largest tidal effect.

40. Effect of the Moon
Places on Earth halfway between the 2 high-tide regions have low tides

41. High and Low Tides
Most coastlines have 2 high tides and 2 low tides each day
Tides are also affected by water depth, coastline shape, and weather

42. Spring Tides
When the Earth, Moon, and Sun are lined up then tides are high tides are higher than usual.
Occur during the full and new moon phases

43. Neap tides
The gravitational pull of the Moon is perpendicular to the gravitational pull of the Sun
During the 1st and 3rd quarter moons
High tides are lower than usual

45. Eclipses
An eclipse is the movement of one solar system object into the shadow of another object

46. Solar Eclipses Occurs during a new moon
During a solar eclipse, a small part of Earth is in the Moon’s shadow
The Moon appears to completely or partially cover the sun

47. Lunar Eclipses A lunar eclipse occurs during a full moon
Earth’s shadow completely or partially covers the Moon.
The Moon is visible during a total lunar eclipse because light changes direction as it passes through Earth’s atmosphere.
The light that reaches the Moon appears red

48. We made it to the end of Lesson 1!