The squares
of the sidereal periods of the planets are proportional to the cubes of
their semimajor axes.
Let's
translate this:
The
squares of 
math
language for a number multiplied by itself:
Example: 6 x 6 = 36

the
sidereal periods of the planets 
we would call this the planet's year
It
is a journey of one full orbit around the sun.

are
proportional to 
are
mathematically related to

the
cubes of 
math
language for a number multiplied by itself
and then multiplied by itself again.
Example:
6 x 6 x 6 = 216

their
semimajor axes. 
We need a diagram here: 
Remember
(Kepler's
First Law) that the planets move in elliptical
paths.
Here
is an ellipse.
The
major axis of an ellipse is a line drawn through both foci.
Here
you can see the major axis drawn in red.
However,
we need to find the semimajor axis.
Semi
means half, so let's cut the major axis in half. Now
we see the semimajor axis in red.
We can use the
mean distance of the planet
from its sun as the number for the semimajor axis.
The mean distance
of the earth from the sun is 93,000,000 miles.
This is called one astronomical unit, or AU
for short.
This law uses the
astronomical unit as the distance number for calculating the length of
the year.
Now you are ready
to calculate the orbital information for your planet,
Find
the Life Zone (Habitability Zone) for Your Planet.
Calculate
the Year Length When You Know Your Planet's Distance from the Sun
Calculate
Your Planet's Distance from the Sun When You Know the
Year Length
© 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
