How do people measure the distance planets are from the Sun?
One means that astronomers use to measure distances to nearby planets is Radio Detection and Ranging, or RADAR. In this method radio waves are transmitted from Earth and bounced off of the planet. Radio waves are a type of light we cannot see with our eyes. Since radio waves travel at the speed of light, the time it takes for radar signals to travel to the planet and back tells us the distance to the planet. That is, the time required for one half of the trip is multiplied by the speed of light to give the distance to the planet. This method only works for planets with solid surfaces. The distances to the more distant Jovian planets may be determined through geometry. For a more advanced discussion of this visit the following website: http://www.astronomynotes.com/solarsys/s2.
