1. Earth Motions Astronomy Page 8 ©Mark Place, 2007-2008

2. How long is one rotation of Earth?
Earth's Motions
How long is one rotation of Earth?
One day - 24 h
How long is one revolution of Earth?
One year d

3. Rising and Setting of the Sun Rising and Setting of the Moon Rotation
Movement of Stars
through the sky
The Seasons
Changing
Constellations
Revolution

4. Earth's rate of rotation?
How do you calculate
Earth's rate of rotation?
One rotation = 360°
Time for one rotation = 24 hours
360° ÷ 24 = 15°/hr

5. How many degrees did the stars move
from diagram 1 to
diagram 2?
30° (2 hours x 15°)

6. It’s the only one that didn’t move
How can you find
Polaris?

7. Finding Polaris
Draw an
Arrow on
Your
picture

8. Because Polaris can only be seen in the North
Northern
Because Polaris can only be seen in the North
What hemisphere
must you be in?
Why?

9. What direction must
you be looking?
North

10. What direction do
the stars appear to
move?
counterclockwise

11. What causes stars
to appear to move?

12. The apparent change in direction of a free swinging pendulum
Evidence for Rotation
Foucault Pendulum
The apparent change in direction of a free swinging pendulum

13. The “deflection” of an object to the right in the Northern Hemisphere
Evidence for Rotation
Coriolis Effect
The “deflection” of an object to the right in the Northern Hemisphere
Plane flying

15. Sidereal day = actual Earth rotation (Ref. Tables)
Solar day = noon to noon
Sidereal day = actual Earth rotation (Ref. Tables)

16. Evidence for Revolution
Changing Constellations
We see different constellations
during different seasons
Parallax