Sept. 16 Make-Up Assignment Part 2

Two kinds of sundials

1. Horizontal sundial: The horizontal sundial is one of the simplest sundials and has been in use since at least the ancient Egyptian and Babylonian times. Obelisks in Egypt are thought to have once been used as sundials. The construction of such sundials is done according to the latitude of the location where the style height of the gnomon (the angle the gnomon makes with the perpendicular) is equal to the latitude and the angle separation of the hour lines can be done according to a formula.

2. Vertical sundial: Similar to the horizontal sundial, the vertical sundial is also constructed according the latitude of its location. This time the style height of the gnomon is also calculated according to a trigonometric formula as is are the separation of the hours lines. Depending on the location and orientation of the sundial, it will be restricted in the amount of daylight hours it can be used. For instance, a direct north-facing vertical sundial in the Southern Hemisphere will only be usable during the hours of 6AM to 6PM. Examples of a vertical sundial can be seen in Ireland in the 7th century.