Kiwanis Chico Community Observatory







Message Group

Orbital Eccentricity Project


Background information:

    Even though the word ellipse might seem uncommon to you, it really isn't.  Ovals are ellipses.  Circles are "perfect ellipses".  The planets in our solar system orbit around the sun in ellipses, in very close to circular orbits.  In this following project, you will learn about what makes an ellipse.  At the very end is a slightly harder project of measuring your ellipse's eccentricity (how off-circular it is).

    The planets in our solar system orbit around the sun in an ellipse.  An ellipse has two foci (plural for focus), the dots to the left.  For a planet's orbit, the sun must be at one of these focii, shown on the left by the yellow dot.  There is nothing at the other focus of the ellipse.


What you need:

1 sharp pencil or pen

2 pieces of tape

1 piece of cardboard (like from an empty cereal box)

1 piece of string or yarn -- at least 6" long


Next Step

Our Sun

Our Moon

Solar System

Deep Sky Objects




Website last updated March 16,  2006.  Hosted by Anthony Watts, KMXI Radio.  Webmasters Tiara Norris and Brendan Diamond.