"Sungames" in Sestri Levante (Genova) - Part 3
Latitude 44° 16' 17" N - Longitude 9° 24' 23" E
Globe sundial (parallel globe)
Globes are not a model of the Earth as seen from Earth, but a model of the Earth seen from space; the Parallel Globe is a model of the Earth differently oriented that gives us some more information than an usual globe; the globe axis lies parallel to the axis of the Earth in the direction in which we will find the North Star at night and the globe is tilted so that the plane of Sestri Levante is positioned at the highest point of the globe and parallel to the ground. This orientation allows to reproduce in miniature the way the Earth is bathed in sunlight; we can see in real time: the rising and setting of the Sun, the areas where it is day or night, where it is noon, where the Sun is at its zenith, what is the lighted Polo, where it is summer and where it is winter, where the shadows are long or short or what happens at the equator.
Ptolemaic plinth (the quadrant)
Ptolemy (fl. second century a.d.) was a great Greek astronomer who contributed to the development of this astronomical instrument. The plinth is a rectangular squared and polished stone, whose plane is adjusted to lie in the plane of the meridian. The gnomon's style is positioned near the upper edge of the Eastward face of the plane in the center of a quarter circle panel graduated from 0° to 90°, representing a quarter of the Sun. When the Sun culminates at local noon reaching its maximum altitude, the shadow of the gnomon projected on the circular sector graduated allows to measure Sun altitude above the horizon. Sun altitude varies throughout the year, reaching a maximum at the summer solstice and a minimum in winter. On the equinox days the shadow indicates the colatitude (90° - latitude), so for Sestri Levante latitude (44.27°) on equinox days Sun altitude will be 45.73°, on winter solstice day about 21° and on summer solstice day about 68°.
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