Sundials were used to tell time from the ancient times, much before any clock device was invented. Sundials require a study of geometry, physics, and other aspects of science. Early sundials had to evolve over many years before time could be accurately foretold. The science of sundials has developed now to such an extent that it is possible to tell the time accurately by using a well-designed sundial.

Basics Of The Sundial

Any object that stands in the sun casts a shadow, and sundials rely on this fact. This shadow moves clockwise on stationary object. This phenomenon was observed by the ancients who then observed that during relative times of the day, lines can be drawn around a stationary object and depending on where the shadow falls, an approximation of the actual time can be made.

The sundial is formed of a base, and a vertical, triangular pointer called a gnomon. The base has numbers all the way around it. sundials are made specifically for each region as the sun shines differently around the globe. Southern hemisphere dwellers should place their sundial numbers closer together during the day and farther apart during night and early morning hours. Northern hemisphere dwellers should keep their sundial numbers closer during both morning and evening hours. This needs to be done since sunlight is available for different amounts of time in each location. The lines around the sundial are not always equally spaced. It’s best to check the latitudes of your region and build a sundial using a sample sundial sheet.

Types Of Sundials

Sundials come in three basic types, though there are many different categories within these types. These are the horizontal dial, vertical south dial and the Analemmatic dial. The horizontal dial is placed parallel to the earth's surface and is the easiest to read, use and adjust. The vertical south dial is commonly placed on a tree or any south-facing object. Such sundials can be focal points of discussion and add beauty to a wall or a vertical object. The Analemmatic dial is placed parallel to the earth's surface, similar to the horizontal sundial. In this kind of dial, the gnomon has to be moved each day into a different hole; there are holes for each day in the year. These dials are not very reliable.

Adjusting Sundials For Better Time

Daylight hours reduce and increase over the course of a year, and Earth’s angle to the sun changes on a daily basis. All these factors let us know that the sundial’s perpendicular shadow to the Earth’s tangent won’t tell time regularly as a clock would. This is because the Earth's orbit slightly elliptical, not a perfect circle, and this curvature makes it difficult to tell the correct time using a sundial. Again, this angle will be different for various latitudes, which means that as each hour passes, the shadow will move depending on the geographic position.

Several factors affect the angle of the sundial; to adjust this, the sundial’s style should be maintained perpendicular to the Earth’s equator, while the sundial’s base should be parallel with the equator. By doing this, you will actually be raising the sundial’s base on the north side so that it is equal to the latitude degree of your location. The sundial’s style is actually the gnomon of a titled sundial.

Even with this adjustment, it’s possible that two different sundials in the same location will read time differently. This happens if the sundials are placed on different lines of longitude. Again, the Earth’s curvature is to be blamed for this, along with the Earth’s spinning motion. One can adjust this time difference by tilting the sundial. The degree of the tilt and the direction in which it is tilted depend on the location and the daylights savings within a region’s time zone.