Sundial (greetings card)

With a rod place into the ground and the sun shining on it, a line was thrown by the shadow. This primitive apparatus was used by the Babylonians, Chinese, Egyptians and the Peruvians. The great obelisk in the Concorde Square in Paris, Saint Peter’s square in Roma and the Hippodrome in Constantinople are no more than ancient solar gnomons. One popular portable sundial design was called a diptych. It consisted of two small flat faces, joined by a hinge. Diptychs usually folded into little flat boxes suitable for a pocket. The gnomon was a string between the two faces. When the string was tight, the two faces formed both a vertical and horizontal sundial. The best material was white ivory, inlaid with black lacquer markings. The best gnomons were black braided silk, linen or hemp. Large (meter-sized) diptychs may have been used for navigation in ancient time. We sell several versions of these - but for now this card is a perfect example. The horologium nocturnum or nocturnal dial is an instrument used to discover the time of night. To do this it uses the fixed stars of the sky; those that have no dusk or dawn and, as such, are always visible.