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Equatorial sundial at Fundación Estadio Fundazioa in Vitoria-Gasteiz. José Ignacio Domínguez.

Of the numerous ways to define a sundial, and after extensive reading on the subject, I consider particularly interesting the definition given by Miquel Palau in his book Rellotges de sol [Sundials], which would translate as follows: ‘A sundial is the materialization of an ingenious idea, so simple it is surprising. It consists of a shadow that moves in the opposite direction to the apparent motion of the sun and aligns with conveniently arranged hour lines’. Nevertheless, the reality of such devices, and a little reflection, shows the art of constructing and using sundials is not quite as straightforward as the definition suggests. As a matter of fact, ancient sundials were not so much the outcome of craftsmanship but of multiple and complex studies. Many people who still today attempt to build sundials without understanding their basic principles rapidly realize their effort is not compensated. It continues to be really remarkable how such a relatively simple instrument can register variations in the earth’s rotation so accurately. (more…)