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Grade 9 Academic Science – Unit 3 Space
Motion of the Celestial Bodies
Section 8.5 Pages 320-328
Celestial bodies include all the objects that orbit the sun. Gravity is the force that keeps the Earth orbiting
the Sun, but it is also responsible for all other orbiting bodies (moon around planets, Comets-Sun,
Galaxies turn)
Orbit and the force of gravity
There is a force of attraction between all objects with mass called
the gravitational force. The greater the mass of an object the
greater its gravitational force (ex. the moon = 1/6 the mass of earth
has a gravity 1/6 that of the earth – you can jump higher on the
An orbiting body maintains orbit due to a balance between the
gravitational pull and its forward speed.
The orbital velocity of the outer planets is much faster and there mass causes them to be much further
away. Earth is one Astronomical Unit away from the sun (AU); Jupiter is 5.2 AU from the sun (five times
1 AU = 150 million km : 5.2 AU = ___________________
Earths Rotation causes the sky to
appear to move from the east to the
west. One rotation equals a day. Earth’s
revolution (orbit) takes 364.25 days
(one year)
Earths Tilt is the Reason for the Seasons on the
Earth. Direct sunlight will hit the Northern Hemisphere in
our summer, at the equator in the spring and in the south
during our winter. The axis is “pointing towards the “North
star”. (23.5o)
The lunar cycle is determined by the position of the moon
around the earth and the reflection. The moon’s gravity
also causes the tides and it is involved in eclipses (see
activities: eclipses, lunar phases)
Day (rotation)
Year (revolution)
Grade 9 Academic Science - Unit 3 Space
Lunar, Solar and Annular Eclipse
For each diagram, use a ruler to draw the light rays to illustrate the appropriate shadow.
1. Solar Eclipse
2. Lunar Eclipse
3. Annular Eclipse (…when the Moon is farther from the Earth than the length of its umbra)
Annular Eclipse – A solar eclipse that occurs when the apparent size of the Moon is not great enough to
completely cover the Sun. A thin ring of sunlight can be seen around the black disk of the Moon.
Lunar eclipse - The passage of the Moon into the shadow of the Earth, always occurring at a full Moon.
Solar eclipse - The passage of the new Moon directly between the Sun and the Earth when the Moon's
shadow is cast upon the Earth. The Sun appears in the sky either partially or totally covered by
the Moon.
Umbra - A complete shadow (as of the Moon) within which the source of light (the Sun) is totally hidden
from view.
If the light source is greater in size than the object causing the shadow, the edges of the shadow will
appear less sharp than when the light source is smaller. The blurred edge is, in fact, a penumbra while
the darker part of the shadow is the umbra.