Patent ID: 7555840

Claim:
A sundial, said sundial comprising: an omni-directional lens including at least two concentric spherical components, said at least two concentric spherical components including a transparent outer sphere having a radius R 1 and an index of refraction n 1 and a transparent inner sphere having a radius R 2 and an index of refraction n 2 ; and a replaceable panel positioned adjacent said omni-directional lens, said replaceable panel being selected from two replaceable panels, each of said two replaceable panels having a semi-cylindrical shape and a surface having marks of date and time thereon, a first one of said two replaceable panels including marks of date and time for a first part of a year and a second one of said two replaceable panels including marks of date and time for a second part of the year; wherein R 1 , n 1 , R 2 , and n 2 are selected so that a parallel beam of sunlight impinging on said omni-directional lens will converge to a sharp spot of light on said replaceable panel thereby indicating a time of a day and a day of a year.