Earth's Rotation Around the Sun

ROTATION

Earth rotates around its AXIS. 

The direction of our rotation is COUNTERCLOCKWISE

The period of rotation for Earth is 24 hours, meaning we rotate at a rate of about 15 degrees per hour.  

 

 

The rate of our rotation is the basis for time zones.  Since Earth rotates 15 degrees longitude every hour we divide the Earth up into different time zones with each one 15 degrees apart.  This makes it so that every time zone is a one hour difference.  

As you travel East each time zone decreases by one hour

As you travel West each time zone increases by one hour.

 

The Axis

THE AXIS IS AN IMAGINARY LINE RUNNING THROUGH THE EARTH FROM THE NORTH POLE TO THE SOUTH POLE (aka the North Star).  

THE AXIS OF THE EARTH IS TILTED 23.5 DEGREES.  THIS JUST MEANS THAT IT DOESNT POINT STRAIGHT UP AND DOWN.  I

OUR TILTED AXIS DOES POINT EXACTLY AT ONE STAR CALLED POLARIS (aka the North Star)

Because our axis always points straight at Polaris we can use it to measure our latitude from any location, by measuring how many degrees it is above the horizon.  

For example, if you are at the North Pole, Polaris will be located directly overhead or 90 degrees above the horizon, and you are standing at a latitude of 90 degrees North.  If you are standing at 45 degrees North latitude you will observe Polaris to be 45 degrees above the horizon.

THE ANGLE OF POLARIS IS THE SAME AS YOUR LATITUDE!

The latitude of the observer is 42 degrees N

The latitude of the observer is 42 degrees N

The latitude of the observer is 66.5 degrees N

The latitude of the observer is 66.5 degrees N

How do we know earth rotates?

Evidence #1:  Focault PEndulum

In 1851 French physicist Leon Focault demonstrated to the world that the Earth rotates through a very simple experiment using a pendulum.

A pendulum essentially a large weight at the end of a rope.  Earlier physicists had already proven that once a pendulum is set in motion, it cannot change direction on its own.

Focault built a massive pendulum suspended from the roof of a cathedral.  Underneath the pendulum, Focault painted a compass on the floor.  To start the experiment he set the pendulum in motion moving directly North to South.  Hours later, when Focault returned he noticed that the pendulum was now moving from East to West.  

SINCE HE KNEW THE PENDULUM COULD NOT CHANGE DIRECTION, THE ONLY POSSIBLE EXPLANATION WAS THAT THE EARTH WAS ROTATING BENEATH IT!

 

EVIDENCE #2:  THE CORIOLIS EFFECT

Have you ever noticed that water always swirls the same way down the drain?

Or that on the weather report, hurricanes always spin the same direction?

Both of these examples are demonstrations of the CORIOLIS EFFECT.

THE CORIOLIS EFFET IS THE DEFLECTION OF FLUIDS LIKE WIND AND WATER CAUSED BY EARTH'S ROTATION.

  • IN THE NORTHERN HEMISPHERE THEY ARE DEFLECTED TO THEIR RIGHT
  • IN THE SOUTHERN HEMISPHERE THEY ARE DEFLECTED TO THEIR LEFT

SINCE THE CORIOLIS EFFECT ONLY OCCURS ON ROTATING BODIES, THE FACT THAT WE CAN SEE IT HAPPENING ALL OVER OUR PLANET PROVES EARTH ROTATES!