
Circle Talk
Circle Equations and
Planet Designing Tips


Use these equations to help you to calculate the area
and volume of your planet.


Some basic
information:
=3.14
r = the radius
The radius is the distance from
the center of a circle to the line that encloses the circle.


Here are some circle formulas that might be useful to you
The
Circumference of a Circle
(the distance around the outside) 
2 p
r

The
Area of a Circle
(the flat surface on the inside) 

The
Surface of a Sphere
(the outside of a ball) 

The
Volume of a Sphere
(the space inside a ball) 

How will we use these formulas?
Note how the numbers change in the examples below.
A change in the radius has quite an effect on the other measurements.
The radii are red in the formulas.
_{*
}means multiplication in the computer.


Radius = 2

Radius = 1

Radius = .5

Circumference of the Circle 
2 p r

2 * 3.14 * 2 =
12.56

2 * 3.14 * 1
=
6.28

2 * 3.14 *
.5
=
3.14

Area of a Circle 

3.14 * (2 * 2)
=
12.56

3.14 * (1 * 1)
=
3.14

3.14 * (.5 * .5)
=
0.785

Surface of a Sphere 

4 * 3.14 * (2 * 2)
=
50.48

4 * 3.14 *
(1 * 1 ) =
12.56

4 * 3.14 *
(.5 * .5
) =
3.14

Volume of a Sphere
(the inside) 

4 * 3.14 * (2 * 2 * 2)
=
33.49

4 * 3.14 * (1 * 1
*1)
=
4.18

4 * 3.14 *
(.5*
.5 .5)=
0.52

When you work out the numbers for your own planet,
you can use these formulas.
If you let the radius of the earth = 1 you can compare
the sizes of the planets with each other without getting entangled
in enormous numbers.
Using the radius of the earth = 1, a larger planet
might have a radius of, perhaps, 1.3.
A smaller planet might have a radius of, perhaps,
0.75.
Check the page on Statistics on Planets
and Moons to get some ideas of possible sizes.
Return to How to Set
Up Your Solar System Page
© 1998, 2003. Elizabeth Anne
Viau. All rights reserved. This material may be used by
individuals for instructional purposes but not sold. Please inform
the author if you use it at eviau@earthlink.net.
