What is the circumference of the Earth? How far around is the
Earth?
The average radius of the Earth is 3,959
miles (6,374 kilometers).
The equitorial diameter of the Earth (distance from one side of
the Earth to the other at the equator) is about 7,926 miles.
The ratio of the circumference to the diameter
of a circle (circumference/diameter)
is written as the symbol pi.
Pi is approximately 3.141592.
3.14159265
3.1415926535
Therefore, to determine the circumference
from the diameter given above:
equitorial diameter x 3.141592 = equitorial circumference
 
7,926 x 3.141592 = 24,900
 
The earth has a circumference of approximately 24,900 miles.
More precisely the circumference of the
earth
at the equator is 24,902 mi / 40,076 km.

How fast would you have to travel to see
the sun set twice,
or outrun the shadow of the setting sun?
Since the sun "travels" once around
the earth every 24 hours,
we can get the speed by dividing the circumference of the earth
by 24:
miles divided by hours
 
24,900 / 24 = 1,038 miles per hour
