How do sun, moon and earth turn around each other? How comes there' seasons, day and night, or the tides. Discover the link to all of it in this GeoGebrabook. Besides applets I created myself some are translations and/or adaptations of existing material I used with most gratitude. Th work of people like Fabrice Vanolli, François Morin, Steven Francis and Marc Dewi Freitag helped me on my way.