Gnomon

swing the sun round the dial.

drag a small watercolour sun around a cut-paper sundial and watch its brass shadow swing the other way, shrinking at noon and stretching at dawn and dusk

shadow bearing = sun bearing + 180 degrees; shadow length = gnomon height / tan(sun altitude), and altitude is lowest at east and west and highest due south.

Concepts: light, rotation, astronomy, time, maps.

An interactive you play with one thumb, on Wundr.