The Gustavianum sun dial
HOW DOES IT WORK?
As the Earth rotates around its axis once every 24 hours, the sun appears to move from east to west during the day. Therefore, shadows will also move during the day. This phenomenon is used in most sun dials.
When the sun shines on the dome’s solar sphere, half the sphere will be illuminated and the other half in shadow. During the day the sun appears to travel across the sky and the boundary line between light and shadow also moves over the surface of the sphere. The position of the line on the sphere shows the time.