How does Tom Egan's sundial work? It reflects light inside without distorting its original direction:
a novel indoor sundial using an externally mounted convex mirror to compress the entire visual arc of the sky down to the size of the mirror. A pinhole in a mask on the window acts as a camera obscura, projecting the image of the sun onto an indoor dial face that can be as small as a letter-size piece of paper. The system has four parts: A convex mirror mounted just above the roof line; a pinhole lens affixed to the window; and two paired flat mirrors to relay the sun beam from the convex mirror through the pinhole and onto the dial face inside the building.