A study unit on the Titius–Bode Law of planetary distances is described. Its format is based on a Piagetian learning cycle of exploration, conceptualization, and applications. More than enough material is provided, including options, for a variety of flexible, open‐ended student activities in an astronomy observatory section faced with a cloudy night. Portions of the unit guide and related ideas may serve as starting points for independent study projects and term papers. The unit is quantitative, employing both arithmetic and algebra; it emphasizes graphical analysis to induce empirical relations.