 The least energy orbit from Earth to another member of the solar system is an ellipse where the shuttle's perihelion, or distance where the shuttle is closest to the Sun, is the point at which the shuttle leaves the Earth's orbit. The shuttle's contact with the larger body occurs at the shuttle's aphelion or point in the elliptical orbit farthest from the Sun. It can be shown that the major axis of the resulting ellipse is found by adding the average distance in astronomical units from the Sun for each of the two bodies together: Earth and the target planet. |
| Communication radio signals travel in space at the speed of light which is 300,000 kilometers per second. Scientists measure communication signals in light years. A light year is a distance and not a time. When a star is 300 light years from Earth, the light left that star 300 years ago, has been traveling through space for 300 years, and is now reaching your eyes. If that same star were to have been blown to pieces or stopped shining 100 years ago, it would be up to our grandchildren's generation of scientists to note the star's change. |
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