zz

1. EARTH'S ROTATION AND
REVOLUTION
Prepare Yourself For
The
Revolution

2. Rotation
Computing the speed of Earth's rotation (at
the equator):
• Circumference of Earth = 40,000
kilometers
• Time for one rotation = 24 hours
• Speed of rotation = Distance/Time =
40,000 km / 24 hr = 1670 km/hr

3. Around and Around We Go
• Every second, that you sit in
this classroom, the Earth's
orbital motion carries you 30
kilometers, or about 18
miles, through space.

4. Revolting Developments!!!
Computing the speed of Earth's revolution
around the Sun:
• Circumference of Earth's orbit =
940,000,000 kilometers
• Time for one revolution = 365 1/4 days =
8766 hours
• Speed of revolution = Distance/Time =
940,000,000 km / 8766 hr = 107,000 km/hr
= 30 km/sec

5. Evidence
• Uniform motion is difficult to
detect. Although it is possible to
detect the Earth's circular
motions, the effects are subtle,
and were not detected until the
18th and 19th centuries, long
after Copernicus proposed that
the Earth was in motion.

6. First line of evidence!
• The Coriolis effect was first described in 1835 by a
French scientist by the name of Gustave Coriolis. If you
are located at the equator, and fire a cannonball north or
south, you find that the cannonball swerves to the east.
Why is this so?
• Demonstration please.
www.theozonehole.com

7. First line of Evidence
• The net result of the Coriolis Effect:
In the Northern Hemisphere, projectiles swerve
to the right. In addition, air rushing inward to a
low pressure area will swerve to the right, and
set up a COUNTERCLOCKWISE hurricane.
• In the Southern Hemisphere, projectiles swerve
to the left, and air rushing inward to a low
pressure area will set up a CLOCKWISE
hurricane.

8. Second line of Evidence
• The Foucault pendulum was first
demonstrated in 1851 by yet another
French scientist; his name was Jean
Foucault. The Foucault pendulum is
nothing more than a very long pendulum
suspended from a well-oiled ball-and-
socket joint overhead, so it is free to swing
in any direction.

9. Foucault Pendulum
http://mxp.physics.umn.edu/s05/Projects/S05SphericalPendulum/foucault-pendulum.jpg

10. Foucault Pendulum
• Foucault set up such a pendulum in the
Pantheon in Paris, and set it swinging
north to south. As hours passed, however,
the direction in which the pendulum was
swinging moved around in a clockwise
direction. After a while, the pendulum was
swinging northeast-southwest; after a
while longer, it was swinging east-west,
then southeast-northwest, then north-
south again

11. Foucault Pendulum
• What causes this change in the pendulum's
direction of swing? The rotation of the Earth, of
course.
• The important fact (independent of where you're
standing) is that the Earth and the pendulum's
swing are rotating relative to each other. If the
Earth did not rotate on its axis, the direction of
swing of a Foucault pendulum would remain
fixed relative to the surface of the Earth.

12. Copernicus
• When Copernicus proposed his heliocentric
theory, his critics pointed out that if the Earth
orbits the Sun once per year, then the Earth's
location in October (for instance) should be 2
astronomical units away from its location in April,
half a year later. This change in the Earth's
location must cause the nearby stars to shift in
apparent location relative to more distant stars.
Could that evidence be seen?

13. Third line of Evidence.
• Stellar parallax was searched for by
astronomers from antiquity onward.
However, prior to the invention of the
telescope, stellar parallax was not
observed.
• Why not?

14. Stellar Parallax
There are two possible hypotheses:
• (1) There is no stellar parallax because the Earth
is stationary. This is the hypothesis put forward
by the supporters of the geocentric universe.
• (2) Stellar parallax exists, but it is too small to be
detected, because the stars are too far away.
This is the hypothesis put forward by Copernicus
and other supporters of the heliocentric
universe.

15. Stellar Parallax
• In fact, stellar parallax was first detected
by Bessel (using a telescope) in the year
1837, nearly three centuries after the
death of Copernicus.
• In general terms, parallax can be defined
as the shift in the observed position of an
object, resulting from a change in the
observer's location.

16. http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/ilt/T041360A.gif

17. Sorry about that.
So, Copernicus was right:
• The Earth does rotate about its axis.
• The Earth does revolve around the Sun.
• The stars are very distant from the Sun.
However, Copernicus wasn't vindicated by
direct observational evidence until
centuries after his death

18. References
• http://www-astronomy.mps.ohio-
state.edu/~ryden/ast161_4/notes13.html
• http://images.encarta.msn.com/xrefmed
ia/aencmed/targets/illus/ilt/T041360A.gif
• http://mxp.physics.umn.edu/s05/Project
s/S05SphericalPendulum/foucault-
pendulum.jpg
• www.theozonehole.com