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The Earth, Moon and Sun
BC Science Probe 9
Sections 12.1 & 12.2
Pages 368-385
Notes
The Earth, Moon, Sun System
A. Movements of the Earth
1. Rotation: Spin of the earth on its axis.
- Takes 23 hours, 56min to complete
- Gives us day and night
2. Revolution:The Earth's motion in it's orbit
around the sun.
a. The Plane of the Ecliptic: The plane which contains the
Earth's orbit around the sun.
This motion takes one year to complete.
b. The Earths Tilt: The earth does not rotate perpendicular
to the plane of the ecliptic. It has a 23.5 degree tilt.
- The star closest to the north rotational axis is
Polaris, the north star. The Earth's axis points in this
direction throughout the year.
c. The Seasons: The direction the Earth's axis
remains pointed in the same direction all year. So
as it travels in its orbit, it appears to change
direction relative to the sun.
This motion takes one year to complete.
d. The Four Seasonal Positions of the Earth
June Solstice: The day with the longest period of
daylight, and the most direct rays from the sun.
Marks the beginning of summer. The reverse for
the southern hemisphere.
December Solstice: The day with the shortest
period of daylight, and the least direct rays from
the sun. Marks the beginning of winter. The
reverse for the southern hemisphere.
d. The Four Seasonal Positions of the Earth
Equinox: The day in which there will be roughly 12
hours of night and 12 hours of day.
- Vernal Equinox: March 21st (marks start of spring)
- Autumnal Equinox: September 21st (marks start of fall)
d. The Zodiac: The twelve constellations the sun
appears to pass through during the year.
These constellations
encircle the ecliptic
ecliptic
- Your “sign” is determined by the constellation the
covered by the sun when you are born.
- You CANNOT see your constellation at night on
your birthday. You have to wait roughly 6 months
before it rises high in the sky
- The twelve constellations of the Zodiac.
There are twelve constellations: Pisces, Aries, Taurus, Gemini, Cancer,
Leo,Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius (this is the
correct order)
- Ancient peoples would often associate different traits to the planets,
and as the planets moved through the various constellations they
predicted things that would happen in your life.
Notes
A. Movements of the Earth
3. Precession: The wobble of the earth on
its axis
- The earth maintains its 23.5 degree
angle but the direction the axis points
changes. Moving in a circle.
- Think of a top spinning on its axis. The
vertical axis begins to wobble over
time.
- This motion of the earth causes the
north star to change.
B. Motion of the Moon
1. The moons orbital period is 27.3 days. The time it takes
to go all the way around the earth.
2. The moons rotational period is ALSO 27.3 days. This is
why only one side of the moon faces the earth. (more to
come)
- Not because it's not rotating, because it rotates at the same
speed it revolves.
3. The Phases of the Moon
- As the moon moves around the Earth, it appears
to change shape. The ENTIRE moon is still present,
but different portions are illuminated.
3. Phases of the moon (continued)
New moon: None is illuminated
Waxing Crescent: Sliver is visible
First Quarter: Half-Full
Waxing Gibbous: Mostly Full
Full Moon: 100% Illuminated
3. Phases of the moon (continued)
Waning Gibbous: Mostly Full
Third Quarter: Half-Full
Waning Crescent: Sliver visible
d. Eclipses: When one object passes into the shadow of
another object.
- Total Lunar Eclipse: When the entire moon
passes into the earth's shadow.
- Partial Lunar Eclipse: When part of the moon
passes into the earth's shadow.
d. Eclipses: When one object passes into the shadow of
another object.
- Total Solar Eclipse: When the moon completely
covers the sun placing part of the earth in
shadow..
- Annular Eclipse: When the moon overlays the
sun but does not block it out completely.
- Partial Solar Eclipse: When only part of the moon
passes over the face of the sun.
Anatomy of an eclipse
Earths shadow
Notes
4. Effects of the Moon on the Earth
a. Tidal bulging: The stretching of the Earth
along the earth-moon line.
- This effect happens whenever one
body moves around another body in
space.
- This happens because the earth is
STRECHED by the gravity of the
moon, not because the moon is
pulling the anything towards it.
- On earth this is noticed as high and
low tides in the oceans.
B. Motion of the Moon
2. Tides: Noticeable daily changes in ocean depth caused
by the gravitational attraction between the earth moon and
sun.
a. Spring Tides: Take place when the Earth, Moon &
Sun are lined up. Cause higher then average high
tides and lower then average low tides.
a. Neap Tides: Take place when the Earth, Moon &
Sun are at right angles to eachother. Cause the
smallest change between high and low tides.
4. Features of the Moon
a. Maria: Large dark areas on the moons surface.
- Large flat plains formed during an earlier volcanic period in
the moons evolution. Lava filled in many of the old craters,
leaving what appeared to be seas.
b. Highlands: lighter coloured areas with elevations
several kilometres above the Maria.
a
b
4. Features of the Moon (continued)
c. Craters: Circular depressions formed when objects
impact the moon.