Maths department > About the department > Sun-dial

Sundial


How this sundial works

In this sundial, time is marked by the shadow of a point, instead of a thin rod as in most sundials. When the shadow of this point falls outside the sundial's frame, it does not have any meaning. The traditional gnomon (the thin rod) has been substituted in this case by a piece of metal represented in the Figure Figura A. The point signaling time is the shadow of the A vertex. The hour lines are eight-shaped. The continuous lines correspond to hours, whereas the dotted ones correspond to half-hours. The eight-shaped hour-lines are coloured in red and black. In winter and spring only the black part has to be considered, and the red one must be discarded. Contrary to that, in summer and winter only the red part has to be considered. The following picture was taken on Jun 17 at 4 PM (14 hours of mean solar time, since our local government, as most governments in Western Europe, have dictated that, in summer, we must go two hours ahead of the Sun). At the time of this picture, the valid coloured part of the hour-lines was the black one. Note that the shadow of the A vertex is on the 14 black hour-line. Note also that the shadow is located between Gemini and Cancer. This means that the corresponding zodiacal sign was one of these two. The sundial also specifies that Gemini corresponds to spring and Cancer to summer. Since Jun 17 corresponds to spring, we were at the Gemini sign on that date. Note also that the shadow is very close to the lower line that goes from Cancer to Gemini. This line corresponds to the summer solstice, that was just a few days ahead (Jun 21).

Let us finally point out that the zodiacal signs are written in Latin: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces. The sundial also includes the following quote from Horace: Urget diem nox et dies noctem (the night pursues the day, and the night the day).

Joan Girbau (1988)

Sundial Functioning of the sundial of the fašade of the faculty

 

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