1. Rotation and Revolution
Aim= Explain the difference between rotation and revolution?
Rotation and Revolution

2. How fast do you think Earth is spinning?
Randy Johnson Fastball: 96 mph
Stock Car average speed: 160 mph
Earth spinning: 1038 mph at the equator
don't be scared!!

3. 1) Earth’s Rotation – Causes daily changes
The spinning of earth on its AXIS – the imaginary line through the planet from the North Pole to the South Pole – is its rotation
The axis of the earth is tilted 23.5° from a line perpendicular to the plane of its orbit of the sun.

4. a) Why do we have night and day?
The side of Earth that faces sun is day
The side that faces away is night

5. Tilt of the axis always stays the same

6. 2) Evidence of Earth’s Rotation
1851, Foucault’s pendulum will appear to change in a predictable way.
Why is this evidence? There is no force acting on the pendulum to make its plane of oscillation rotate or go around its own axis
It would continue to swing in the original path if Earth did not rotate.

7. No force that makes pendulum rotate – must be earth that is rotating!!!
Inertia and gravity make it swing straight out and straight down in a straight arc – not twist.

9. 3) Evidence for Rotation
Coriolis Effect – the tendency of objects moving over the earth (air, water, planes, projectiles) to be deflected (curve away) from a straight line path. The French scientist, Gaspard Coriolis, first explained the deflection of objects moving over the surface due to Earth’s rotation
The deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
This deflection occurs because Earth’s surface is rotating with respect to the objects.

15. What are the APPARENT MOTIONS of Celestial Objects
An apparent motion is a motion an object appears to make
An apparent motion can be real or an illusion
For example, the stars appear to move across the sky from east to west
However, the apparent motion is caused by Earth’s rotation

16. Stars in constellations are often very far from one another but we see them in the same direction in the sky.
Big Dipper

17. Pointer Stars point to Polaris

18. Some Definitions Celestial Sphere: A huge imaginary sphere around
the Earth to which the stars appear to be
attached.
Constellation: An arbitrary grouping of stars in the
Sky that are in the same general direction. The
modern ones are fixed by international
agreement to map the entire Sky.
Celestial Equator: Projection of the Earth’s Equator
onto the Celestial Sphere.

19. Imagine all the stars moved down onto a big glass sphere around the Earth.
Celestial
equator

20. Stars
celestial sphere is stationary
Earth Rotates Counterclockwise

21. Looking upward we see the stars fixed on the celestial sphere
Earth’s eastward rotation makes the stars between the equator and north celestial pole appear to move westward
Rise in the east and set in the west.
Timed photography showing stars rising in the east

22. Stars appear to be moving from east to west. Stars rising in the east.

23. Stars appear to be moving from east to west
Stars appear to be moving from east to west. Rise in the east and set in the west.

24. Northern part of the sky around Polaris
CCW
Moving west to east

25. Earth’s counter clockwise rotation makes the stars appear to rotate counter clockwise around the north celestial pole (Polaris).

27. The complete circular path can be seen for stars in the northern part of the sky around Polaris
Circumpolar constellations never set.
Circumpolar constellations change with latitude… sky changes with latitude

28. 4) Daily Motions
Some of the stars near Polaris appear to move in a complete circle in 24 hours.
The paths of all celestial objects moving in the sky are circular or parts of a circle called an arc.
All motion occurs at a constant rate of approximately l5° per hour or 360° in 24 hours.

29. 5) Earth’s Revolution
Earth revolves around the sun in a slightly eccentric elliptical orbit or path once a year
It takes Earth days to revolve 360° in its orbit around the sun. It moves approximately 1° per day. (360°/ days = 1° per day)

30. 6) Evidence of Earth’s Revolution around the Sun
Seasonal Constellations: Because of the Sun’s annual motion, some constellations are visible at night only during certain seasons.
Constellations are visible when the dark side of Earth (away from sun) faces toward the constellation.

31. The 13 constellations the sun appears to travel through during the year

32. Different constellations at different times of the year

33. 7) Evidence of Revolution Parallax Shift
Because of Earth’s revolution about the sun, near stars seem to shift their position against the farther stars (closer star – greater the shift)
If you observe the same star while earth is at 2 different points during its orbit around the sun, the star’s position relative to the more distant background stars will appear to change.

36. Parallax Shift

37. 8) Apparent Motion of Sun due to Rotation and Revolution
Rotation: Sun – apparent daily path from sunrise to sunset has the shape of an arc moving l5° per hour.
Revolution: However, the sun’s arc changes both its position and its length with the seasons

39. Earth’s Revolution around the Sun – the tilt of Earth’s axis does not change producing a cyclical change of seasons

40. 9) Summary Rotation: Earth rotates l5° per hour in 24 hours.
Revolution: Earth takes days to revolve around the sun moving approximately 1° per day.