Although strictly, the term planet applied only to those five objects, the term was latterly broadened, particularly in the Middle Ages, to include the Sun and the Moon (sometimes referred to as "Lights"), making a total of seven planets.
Selvom betegnelsen "planet" kun gjaldt disse fem objekter, blev betegnelsen senere udvidet, specielt i Middelalderen, til også at gælde solen og månen (nogen gange kaldet "Lys"), så der i alt var syv planeter.