Nine planets plus 2 key cards. Twenty cards in total. I got an online planetarium, which I put together, painted and use it to introduce the planets alongside these cards. This led to studying gravity and a lot of excitement about space, the planet earth, the moon, astronauts... We have just talked about Mars, and I discovered that Mars is one of the most explored planets, so, while in Barnes and Noble (looking for a birthday card for my daughter), I spy a beautiful book called Red Planet in the 75% off section, who could resist. Needless to say, that will be going into Children's House with me once I have had a chance to look it over.