Well the Solar System I knew back then had 9 planets (Pluto was still a planet then) and of the moons Earth had one, Mars two, Jupiter 12, Saturn 9, Uranus 5 and Neptune 2 , totaling 31 (Jupiter and Saturn alone now have almost that total number each). Then in 2006 this changed, Pluto got demoted and now, as this tee shirt suggest: there are only eight planets.

To understand why Pluto isn’t a planet, perhaps it helps if we define what the term planet means. The expression goes back to ancient times and comes from the Greek word for “wandering star.” Because the planets are bodies that move in orbit around the sun, they do not stay in a fixed location in the sky in relation to the stars.