When you look up at the night sky it can be extremely difficult to distinguish which point of light is a star and which is a planet. Today it is easy because we have powerful telescopes to give us images that can show us the planets... even in great detail! Now try to picture yourself back in the time of ancient Greece. You might be sitting outside on a clear night and star gazing into a beautiful, luminescent sky. Remember that it is completely pitch black at night because they did not have the power of electricity that lights big cities and in turn dims our view of the night sky. How would you pick out the planets without any sort of instrument to magnify your view? For centuries the Greeks observed the night sky and wrote down everything they saw. Finally they were able to pick out five bodies that behaved peculiarly and named them the planets: Mercury, Venus, Mars, Jupiter, and Saturn. (Uranus, Neptune, and Pluto were not discovered until modern times with the aid of powerful telescopes because of their great distances from the Earth.)

The word planet (in Greek, planets) means wanderer. They called these peculiar heavenly bodies wanderers because the path they followed over a period of time was not consistent with all the other bodies in the sky. They would appear farther to the east each night and occasionally seemed to slow down and move backwards (retrograde) for a month or two. I know that this sounds confusing and it was to the Greeks, but by being confused by these wanderers they were able to distinguish them from the rest of the heavens. This strange path of the planets is called retrograde motion. The planets appear brighter when they are closest to the Earth during the retrograde points of their orbits.

Before the Romans went and changed their names, the planets were named by the Greeks for their gods. For example, Mercury was named Hermes and Venus was named Aphrodite. When the Romans changed their names they simply renamed them to their own gods.