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

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

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

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

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

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

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” http://www.youtube.com/watch?v=rcquRMaVSKU 0:00-2:30 min Do Lesson 14 “What causes the change of the seasons?” booklet as a class

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

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

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

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

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