1. 7.3 Movements of Earth and the Moon
Why is it important to understand the Earth’s movements?
Understanding Earth’s rhythms is critical to the understanding of the life cycles of all living things
The seasons are a result of Earth’s revolution around the sun
The Earth performs two kinds of movements, what are they called again? Revolution (just mentioned) and rotation about an axis

2. Why is it important to understand the Moon’s movements?
The Moon is responsible for the tides that occur on Earth
The tides are the rising and falling of ocean waters
The orbit of the Moon around the Earth results in the phases of the Moon, as well as eclipses
The Moon is our closest neighbour in space

3. Earth’s Motion As a result of Earth’s rotation
everything in the night sky appears to
rise in an easterly direction and set in a westerly direction
As a result of Earth’s revolution
around the Sun, you see different
constellations at different times
of the year

4. The path of Earth’s orbit around the Sun is not a perfect circle, it is an ellipse
A circle has one centre point
Whereas, an ellipse has two points called focal points, which define the shape of the ellipse

5. The Sun is at one focal point which defines the shape of the ellipse
So, at one focal point in Earth’s elliptical orbit Earth is closest to the Sun
And at another point, Earth is farthest from the Sun
What is another name for orbit? Rotation or revolution? Revolution

6. Why do we experience seasons?
Earth does not rotate in an upright position
It rotates on an axis tilted at 23.5o from the flat plane of Earth’s orbit and that tilt does not change
In the summer months, the northern hemisphere is tilted toward the Sun
In the winter months, the northern hemisphere is tilted away from the Sun
What do you think happens in the southern hemisphere? The same or the opposite? Opposite

7. Light rays that hit the Earth straight on are called direct rays
As a result of Earth’s tilt, sunlight strikes Earth’s surface at different angles
Areas that receive sunlight at larger angles receive more sunlight for longer periods of time
Light rays that hit the Earth straight on are called direct rays
Light rays that do not hit the Earth straight on and are slanted to some degree are called indirect rays
Refer to “Lesson 14: What causes the change of seasons?” booklet for more information
Video: “What causes the Seasons” 0:00-2:30 min
Do Lesson 14 “What causes the change of the seasons?” booklet as a class

8. The Moon’s Motion
During the night, the Moon appears to move across the sky with the stars and the planets due to Earth’s rotation
The Moon also appears to move from west to east as it moves in its orbit
The Moon makes a
complete orbit around
Earth in about 27.5 days

9. As a result, you always see the same side of the Moon!
As the moon completes one orbit around Earth, the Moon rotates only once on its axis
As a result, you always see the same side of the Moon!
The other side of the Moon is nicknamed “the dark side of the Moon” for this reason
However, the other side of the Moon does receive sunlight for about two weeks (therefore, not always “dark”)
The first time the “far” side of the Moon was viewed was in 1959 when the Soviet Union launched a spacecraft that passed behind the Moon and photographed the opposite side

10. Phases of the Moon The Moon is always half illuminated by the Sun
But how much of the illumination you see depends on where the Moon is relative to Earth
We classify the amount of illumination we see as the phases of the Moon

11. Phases of the Moon: the monthly progression of changes in the appearance of the Moon, which result from different portions of the Moon’s sunlit side being visible from Earth
Waxing means increasing
Waning means decreasing
Gibbous means that the amount of light we see illuminating the Moon is between half lit and fully lit

12. Homework: Lesson 17: What are the phases of the Moon? booklet