Step 1-Background The Background step of this activity provides a list of observations of the contents and characteristics of the Solar System, and emphasizes that any theory must address these observations. The nebular theory is introduced as the one that most comprehensively describes the formation of the Solar System. 1. Pick two of the above observations that could be observed from Earth without any special equipment. Answers might vary, but the total list includes: Planets are located on or close to the ecliptic. (Alignments in the sky.) Planets all orbit in a counterclockwise direction. (Would need to chart planets over months.) The planets and moons with solid surfaces all have evidence of cratering. (Students might include this one because craters on the Moon can be seen with binoculars, which probably aren't considered special equipment.) _ Meteorites show evidence of being made up of even smaller chunks of material. (Just need a sample of a chondrite.) Suggested discussion topic: After students answer question 1, engage them in a think-pair-share activity to compare the observations they chose