Unit III: The Earth in Space
Celestial Objects
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Any natural object “outside” the earths
atmosphere (seen in the sky)
Celestial Sphere
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The imaginary sphere on which all objects
in the sky appear on.
How do celestial objects move in
the sky?
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Apparent Daily Motion: the apparent motion
of celestial objects in a path from east to west
in the sky over a 24 hour period.
Why is it called “apparent motion”?
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The objects themselves DO NOT MOVE—
the Earth ROTATES (spins)
Tractor Trailer Effect
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Celestial objects appear to move along a
curved path called an ARC.
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Constellations: groups of a few stars that
form a pattern in the sky
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Examples- Big Dipper, Little Dipper, Orion
Models of the Night Sky
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Geocentric Model: shows the Earth in the
center of the universe and everything else
revolving around it.
(Earth does not move)
THIS IS WRONG!!!!!
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Heliocentric Model: sun in the center of
our Solar System and the Earth and other
planets revolving around it.
This is Correct!
The Heliocentric Model Takes Two
Earth Motions Into Account
1.
The Earth rotates (spins) on its axis at a
rate of 15° per hour (daily motion)
2.
The Earth revolves (orbits) around the
Sun at a rate of 1° per day (annual
motion)

Period of Revolution: amount of time it
takes an object to go around the sun
once.
How do we know that Earth really
rotates on its axis?

Foucault Pendulum: swinging weight that is
free to rotate as it swings back and forth. As
the Earth rotates, the pendulum changes
direction.

Coriolis Effect: apparent curving of
objects to the right in the Northern
Hemisphere (counterclockwise spin)
How do we know that Earth revolves
around the sun?
1.
2.
Seasons
Changing Constellations (at different times of
the year you see different constellations)
Apparent Motions of the Sun
***The Sun, just like other stars, rises in the
east and sets in the west because of
Earth’s Rotation

Apparent Solar Day: the interval of time
during which the Sun passes from its
highest point on one day to its highest
point on the next.

Solar Noon: sun’s highest point in the sky
during the day
**the Sun’s apparent speed never changes
Shadows….
The higher the sun is in the sky, the
shorter the shadow
 Shadows occur opposite the sun

afternoon
morning / evening
This shows up all the time!
Which direction do the Sun and
stars appear to move?

When looking east, west, or south, stars
will appear to move to the right
Eastern Sky
Western Sky

When looking north, stars will form circles
around Polaris (remember Polaris NEVER
moves)
Seasons
What causes seasons on Earth?
1.
Tilt of the Earth’s Axis of 23 ½ º
2.
Parallelism of the Axis: regardless of
the Earth’s position the axis always
points in the same direction as it revolves
****the cause of the seasons IS NOT DUE to
the fact of how close the Earth is to the
Sun—in fact the Earth is closest to the
Sun in January because of Earth’s
elliptical orbit

Tropic of Cancer: an imaginary line that
is located 23 ½ degrees north of the
Equator

Tropic of Capricorn: an imaginary line
that is located 23 ½ degrees south of the
Equator
**the Sun will only get directly overhead (Zenith)
between the Tropics
**the equator always gets 12 hours of daylight!!!
Four Important Days in Earth Science:
1.
Summer Solstice:
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June 21st
Northern hemisphere is tilted towards the Sun
Insolation (incoming solar radiation) is most
direct (sun highest in the sky)
Longest Day of the year in the Northern
Hemisphere
Sun is directly above The Tropic of Cancer at noon
Sun rises north of east and sets north of west
Summer Solstice
2.
Autumnal Equinox
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September 23rd
Day and night are equal (Equinox: “Equal
Night”)
Sun is directly over the Equator at noon
Sun rises due (exactly) east and sets due
west
Autumnal Equinox
3. Winter Solstice:
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December 21st
Northern Hemisphere is tilted away from the Sun
Insolation is least direct (sun lowest in the sky)
Shortest day of the year in the Northern Hemisphere
Sun is directly above The Tropic of Capricorn at
noon
Sun rises south of east and sets south of west
Winter Solstice
4. Vernal Equinox:
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March 21st
Day and night are equal (Again, Equinox
means “equal night”)
Sun is directly over the equator at noon
Sun rises due east and sets due west
Vernal Equinox
Winter
Date of First Day
Scientific Name
Direct Rays of the Sun Hit
What is Happening Inside
the Arctic Circle?
What is Happening Inside
the Antarctic Circle?
How much daylight do we
get on First Day in NYS?
How many degrees is the
Earth Tilted?
Altitude of noon sun in NYS
Spring
Summer
Fall
Seasons Review
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The tilt (or “inclination”) is the reason for the seasons
Temperature changes because the Sun’s rays strike the
earth at different angles (high altitude = high temp.)
Insolation = Sunlight
On the equinoxes, the Sun is directly over that equator at
noon
On the summer solstice, the Sun is directly overhead
The Tropic of Cancer at noon
On the winter solstice, the Sun is directly overhead The
Tropic of Capricorn at noon
The Lower the Sun is in the sky, the longer the shadow
The equator always has 12 hours of daylight
**Remember**
**The Sun ONLY gets 90° (directly
overhead in the tropics (23 ½º N
and 23 ½º S)**