Omni-directional Lens in Sundials and Solar Compasses

摘要

To date, the existing sundials and solar compasses use a gnomon, such as a stylet, to project a shadow under the sun on a marked surface to find the time or the true north. Because of the fussiness of the shadow and the dependence of the position of the sun with the day of the year (equation of time), the accuracy is low. The present invention discloses an omni-directional lens, which can focus the sun beam into a sharp spot with a long depth of field. By projecting the spot on a cylindrical panel, both the day of the year and the time of the day can be read off simultaneously with very high accuracy. Because of the simultaneous displaying of time and date, no equation-of-time correction is required. If the time is known, the true north can be determined with high accuracy, and the device becomes a reliable and easy-to-use solar compass. 4,384,408 Bohlayer 1983 4,520,572 Spilhaus 1985 4,835,875 Fuller 1989 4,945,644 Fuller 1990 5,197,199 Shrader 1993 5,425,178 Steele 1995 6,301,793 Gottesman 2001 6,604,290 Gottesman 2003 7,114,262 Andrewes 2006 9,428 Burt 1836 4,899.451 Dandurand 1990 5,425,178 Steele 1995 5,459,931 Waltho 1995