Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
Earth's Rotation
Earth's Rotation and the Apparent Daily Motion of the Sky
The Earth rotates around the axis. Earth revolves around the Sun once a year (365.25
days/12 months). To an astronomer…




“rotate” = spin around an axis.
one time around the axis = one rotation (also called a day!).
“revolve” = orbit around the Sun.
one time around the Sun = one revolution (also called a year!).
For an observer, the rotation of the Earth makes it appear as if the sky is revolving
around the Earth. In other words, if you are standing for long enough in a field at
night, it looks like the sky is moving, not you.
Time in Daylight
In the diagram to the left, we see the Earth
tilting towards the Sun. The dot represents
Brigham City. During the summer, we
spend more time in sunlight than darkness.
Look at the line and dotted line (representing
the amount of time spent in darkness). The
lines show the difference.
Time in Darkness
DaDarknessyligh
t
In the diagram to the right, we see
the Earth tilting away from the Sun.
The dot represents Brigham City.
During the winter, we spend more
time in sunlight than darkness. Look
at the line and dotted line
(representing the amount of time
spent in darkness). The lines show
the difference.
Time in Daylight
Time in Darkness
DaDarknessyligh
t
1
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
Why is Earth rotating? Did it always have the same rotation period?
Will it always have the same rotation period?
(source: NASA Space Place)
Earth's graceful 24-hour rotation rate helps make our planet so friendly to life. Most
parts of Earth to stay a nice, comfortable temperature as they are bathed in sunlight
during the day and darkness at night.
Each planet in the Solar System has its own unique rotation rate. Tiny Mercury,
sizzling closest to the Sun, takes 59 Earth days to turn around just once. Venus, the
second planet, rotates once every 243 Earth days. What's more, Venus rotates
backwards from the direction of its orbit around the Sun, as do Uranus and tiny dwarf
planet Pluto. Uranus even lies down on the job, rolling around with its axis of rotation
pointed nearly toward the Sun.
Why do Earth and the other planets rotate at all? It will help to understand how our
Solar System formed. Almost five billion years ago, our Solar System had its
beginnings as a vast cloud of dust and gas. The cloud began to collapse, flattening into
a giant disk that rotated faster and faster, just as an ice skater spins faster as she brings
her arms in. The Sun formed at the center, and the swirling gas and dust in the rest of
the spinning disk clumped together to produce the planets, moons, asteroids, and
comets. The reason so many objects orbit the Sun in nearly the same plane (called the
ecliptic) and in the same direction is that they all formed from this same disk.
While the planets were forming, there was not much peace in our Solar System.
Clumps of matter of all sizes often collided, and either stuck together or side-swiped
each other, knocking off pieces and sending each other spinning. Sometimes the
gravity of big objects would capture smaller ones in orbit. This could be one way the
planets acquired their moons.
Scientists think that a large object, perhaps the size of
Mars, impacted our young planet, knocking out a
chunk of material that eventually became our Moon.
This collision set Earth spinning at a faster rate.
Scientists estimate that a day in the life of early Earth
was only about 6 hours long.
2
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
The Moon formed much closer to Earth than it is today. As Earth rotates, the Moon's
gravity causes the oceans to seem to rise and fall. (The Sun also does this, but not as
much.) There is a little bit of friction between the tides and the turning Earth, causing
the rotation to slow down just a little. As Earth slows, it lets the Moon creep away.
We can use extremely accurate atomic clocks to measure exactly how much the
rotation is slowing down. One hundred years from now, a day will be about two
milliseconds longer than today. Two milliseconds is 1/500th of a second, or how long
it takes a car going 55 mph to travel only two inches--in other words, much less than
the blink of an eye. So, if you live to be 100, you can't complain that the days are
getting shorter! At this rate, though, you don't have to worry about the days getting
enough longer to change things very much.
3
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
Name ______________________________________________________________
Earth’s Rotation & Revolution – Worksheet
1. Earth rotates around its axis once every __________ hours. (Enter a number)
2. Earth revolves around the Sun once every __________ days. (Enter a number)
3. Standing on the Earth, it looks like the sky is rotating around the Earth.
a. True
b. False
4. In the summer, Brigham City spends __________ time in darkness.
a. less
b. more
c. the same amount of time
5. In the winter, Brigham City spends __________ time in daylight.
a. less
b. more
c. the same amount of time
6. Mercury takes __________ Earth days to rotate once. (Enter a number)
7. Venus takes __________ Earth days to rotate once. (Enter a number)
8. Identify which planets/dwarf planets rotate backwards from the direction of its
orbit around the Sun. (There are three answers to this question. Enter all three
answers in your clicker.)
a. Venus
b. Uranus
c. Saturn
d. Pluto
e. Neptune
f. Mercury
g. Mars
h. Jupiter
i. Earth
j. Ceres
4
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
9. Planets rotate because the original cloud from which the Solar System formed began
to collapse into a giant disk that rotated…
a. slower and slower.
b. faster and slower.
c. slower and faster.
d. faster and faster.
10. When Earth was hit by a large object the size of Mars, it caused the Earth to rotate
at a __________ rate.
a. faster
b. slower
11. A day in the life of early Earth lasted __________ hours. (Enter a number)
12. As Earth rotates, the Moon’s gravity causes the __________ to seem to rises and
fall.
a. atmosphere
b. land
c. ocean
13. The tides cause Earth’s rotation to slow down a little. As Earth slows, it lets the
Moon __________ Earth.
a. creep away from the
b. creep closer to the
c. stay the same distance from
14. One hundred years from at day will be 1/500th of a second longer than it is today.
This is how long it takes a car going 55 mph to travel __________ inches. (Enter a
number)
5
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
Earth’s Rotation & Revolution – Worksheet – Key
1. Earth rotates around its axis once every __________ hours. (Enter a number)
24
2. Earth revolves around the Sun once every __________ days. (Enter a number)
365.25
3. Standing on the Earth, it looks like the sky is rotating around the Earth.
a. True
b. False
a. True
4. In the summer, Brigham City spends __________ time in darkness.
a. less
b. more
c. the same amount of time
a. less
5. In the winter, Brigham City spends __________ time in daylight.
a. less
b. more
c. the same amount of time
a. less
6. Mercury takes __________ Earth days to rotate once. (Enter a number)
59
6
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
7. Venus takes __________ Earth days to rotate once. (Enter a number)
243
8. Identify which planets/dwarf planets rotate backwards from the direction of its
orbit around the Sun. (There are three answers to this question. Enter all three
answers in your clicker.)
a. Venus
b. Uranus
c. Saturn
d. Pluto
e. Neptune
f. Mercury
g. Mars
h. Jupiter
i. Earth
j. Ceres
a. Venus; b. Uranus; d. Pluto
9. Planets rotate because the original cloud from which the Solar System formed began
to collapse into a giant disk that rotated…
a. slower and slower.
b. faster and slower.
c. slower and faster.
d. faster and faster.
d. faster and faster.
10. When Earth was hit by a large object the size of Mars, it caused the Earth to rotate
at a __________ rate.
a. faster
b. slower
a. faster
11. A day in the life of early Earth lasted __________ hours. (Enter a number)
6
7
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
12. As Earth rotates, the Moon’s gravity causes the __________ to seem to rises and
fall.
a. atmosphere
b. land
c. ocean
c. ocean
13. The tides cause Earth’s rotation to slow down a little. As Earth slows, it lets the
Moon __________ Earth.
a. creep away from the
b. creep closer to the
c. stay the same distance from
a. creep away from
14. One hundred years from at day will be 1/500th of a second longer than it is today.
This is how long it takes a car going 55 mph to travel __________ inches. (Enter a
number)
2
8
Objective – Identify the difference between the motion of an object rotating on its axis and an object revolving in
orbit.
Earth’s Rotation & Revolution – Worksheet – Scoring Guide
13-14 – 4
11-12 – 3.5
9-10 – 3
8 – 2.5
7–2
6 – 1.5
5–1
1-4 – .5
0–0
9