Heavenly Bodies

Shabbos 156a, among other sources, lists 7 heavenly bodies visible from the earth. Chamah, the Sun, is so called because it is the source of heat. Levana, the moon, is so called because it looks white. Nogah, Venus, is so called because it is the brightest of the "smaller bodies" visible from earth. Ma'adim, Mars, appears red from earth because its surface is covered in rust. Shab'tai, Saturn, has the 7th longest cycle out of the heavenly bodies (as it has the longest orbit - Uranus, Neptune, and the Kuiper-belt-object-nee-planet Pluto are not visible with the naked eye).

Mercury is known as Kochav, meaning "Star". According to Wikipedia, this term is short for "Kochav Chamah", the Star of the Sun, since Mercury is the closest to the Sun.

The remaining heavenly body is Jupiter, known as Tzedek, righteousness. It seems that this would have to do with the planet's largest size amongst the other smaller bodies, which led a number of ancient peoples to tag the planet with the name of their chief deity. Perhaps Tzedek was therefore a euphemism to avoid using an idolatrous name for the planet.