Peter explains where the sand on our beaches comes from, why it is sometimes fine and sometimes coarse and why the colors of the sand can vary on beaches around the world.
Videoclip: Planetopia – Woher kommt der Sand am Meer?

In the second video Peter explains why everything looks blurry under water, what our eyes have in common with magnifying glasses and how light beams behave at the transition between air and water.
Videoclip: Planetopia – Warum sehen wir unter Wasser unscharf?