Name ______________________________
Period __________
Motions of Earth, Moon, and Sun
Apparent Motions of Celestial Objects
An apparent motion is a motion that an object __appears____ to make.
When an ice-skater is spinning with their eyes open, the room appears to
be spinning. The spinning room is an illusion.
I.
Daily Motion and Stars
1. Most celestial objects appear
to move across the sky,
rising in the _eastern___ part
of the sky and setting in the
___western part___
2. In the north, stars appear to
make a counterclockwise
__arc___ around the North
Star, or __Polaris___. In 24
hours, the stars appear to
make a complete circle.
3. The apparent movements of
celestial objects in a 24-hour
period are called _daily__
motion.
4. This motion is caused by the
Earth’s ___rotation____.
The actual motion is the
Earth spinning and the stars
sitting motionless.
II.
Apparent Motions of the Planets
1. As seen from Earth, the planets look like stars and show the same apparent
daily __motion___ like the stars (rise in East, set in West).
2. However, over a few weeks or months, the planets appear to change
_position__ with respect to the background field of stars around them. The
stars do not change positions (in your lifetime).
3. This is because the Earth and the planets (Jupiter, Mars, Venus, etc.)
__orbits_____ our Sun (a star), while the stars are trillions of miles away.
4. Since each planet orbits the Sun at a different ____speed___ and a different
__distance___, then the apparent motion of the planets as viewed from Earth
are not in a smooth arc across the sky.
III.
Apparent Motions of the Moon
1. The Moon also follows the ____daily______ east-to-west motion of the stars
due to the Earth’s rotation.
2. However, it appears to rise about ___50___ minutes later each day and shifts
____eastward______ each day compared to the background field of stars.
3. This is because the Moon __orbits____ the Earth in a 27 day period.
IV.
Apparent Motions of the Sun
1. Like all other visible celestial
objects, the Sun also seems
to __move___ in the sky.
2. The Sun’s apparent path
from sunrise to sunset, has a
shape of an _arc__, and is
called a ___diurnal___ circle.
One circle equals __24_
hours.
Winter Solstice
Equinoxes
Summer Solstice
3. Where it rises in the eastern sky and sets in the western sky __changes__
throughout the year, which has an effect on how long the Sun is up.
a. The greater the length of the Sun’s path over an area, the more hours of
___daylight_____ the area has. (day + night still equals 24 hours)
b. Daylight is longest in __summer___ and shortest in __winter_____.
c. Winter Solstice – __Dec 21____________, lowest noon Sun
[sunrise is 23.5 degrees south of east]
[sunset is 23.5 degrees south of west]
d. Summer Solstice - ____Jun 21___________, highest noon Sun
[sunrise is 23.5 degrees north of east]
[sunset is 23.5 degrees north of west]
e. Vernal Equinox - ____Mar 21___________, exactly 12 hours of daylight
[sunrise is due east and sunset is due west]
f. Autumnal Equinox - ___Sept 23_________, exactly 12 hours of daylight
[sunrise is due east and sunset is due west]
4. Only between latitudes 23.5 North and 23.5 South can the noon Sun be
directly overhead at the ____zenith_____.
5. So, the noon Sun is ___never_________ directly overhead anywhere in the
continental United States.
Actual Earth Motions
I.
Rotation of Earth (spin)
1. The Earth’s axis is an imaginary line through the planet from the
____north____ Pole to the ____south_____ Pole.
2. The __spinning____ of Earth on its axis is its rotation.
3. The axis of the Earth is tilted ____23.5____ degrees from a line
perpendicular to the Earth’s orbit around the Sun.
4. We (at about 45 degrees latitude) are rotating around the Earth at about 500
miles per hour. If this is true then why can’t we feel it? No acceleration
5. Evidence of Earth’s rotation
a. The Foucault Pendulum – If the Earth did not rotate (spin), then a
swinging pendulum should go back-n-forth along one ___path____
indefinitely, but it doesn’t. The back-n-forth path of a pendulum actually
rotates a full 360 degrees in __24____ hours. In reality, the swinging
pendulum does not change its path. The Earth is actually rotating
_____underneath____ the pendulum.
b. The Coriolis Effect – Fluids (wind and ocean currents) _deflect__ to the
right in the Northern Hemisphere and deflect to the left in the Southern
Hemisphere. Similar to the Foucault Pendulum, the moving fluid actually
creates a straight path, but the Earth _moves__ underneath it.
II.
Revolution of the Earth (orbit)
1. The Earth __revolves____ around the Sun in a slightly eccentric
__elliptical____ orbit, or path, once a ___year____.
2. A Constellation is a group of stars that form a _____pattern_____ and are
used to help people locate celestial objects. The positions of stars are
completely ___random_____, and constellations are only made-made.
3. At night you can see _different_____ constellations at different times of the
year. This is evidence that the Earth orbits the Sun as shown in the diagram.
Models That Help Explain Apparent Celestial Motions
I.
II.
Geocentric Models
1. This model states that the __Earth_____ is the center of the solar system and
universe, and explains most of the motions of celestial bodies.
2. The Earth is stationary (not moving) and all celestial bodies orbit the Earth,
which _explains___ the daily motions of the Sun, Moon, planets, and stars.
3. This was largely accepted in Europe until the 16th century.
Heliocentric Models
1. This model states that the ____Sun___ is the center of the solar system, and
explains the apparent motions of all celestial bodies.
2. The Earth rotates (spins) on an imaginary __axis__ and revolves around the
Sun in an __orbit____.
3. The _planet__ also rotate on an axis and revolve around the Sun in an orbit,
while the Moon orbits the Earth.
Early heliocentric models incorrectly assumed that orbits were _circular__, which did not
allow for accurate predictions of future planetary positions.