Earth in Space : Gravity and Orbits By Colorado University
This excellent simulation depicts the orbit of the Earth around the Sun and to show the effects of increases and decreases in the gravitational force governing the Earth’s orbit.
In addition, there is an option to show the orbit of the moon around the Earth.
Users can increase ir decrease the gravitational pup of the sun or the earth and watch the effects on screen. The orbit may change its distance from the Sun or become elliptical depending on the relative gravitational force of the two celestial bodies.
In extreme cases the Earth may even crash into the Sun or drift off into outer space.
This activity is both instructional and provides great subject matter for discussion about what wold happen to life on Earth in a variety of circumstances