Sun clocks or sundials are the oldest device known to man that was and still are used to tell time. The principle behind a sundial is very simple. As the sun rotates around the earth and moves from east to west, it casts a shadow. This shadow is then used to predict time.
Egyptians were the first ones to use sundials. These beginning time telling devices consisted of a t-shaped cross ban with a vertical stick. This stick was marked with five lines that represented five hours. In the morning, the stick was placed facing east and measured the next five hours. Afternoon times were measured by moving the stick so that if faced the west.
Later on, obelisks were built by the Egyptians and Babylonians that were used to calculate time. These structures were very important in the calculation of the longest and shortest days of the year.
Eventually, smaller, more portable sundials were designed that resembled smaller versions of the obelisk.
The Greeks created sundials called “pelekinon.” This type of sundial consisted of a gnomon or vertical rod that was placed on a horizontal or half-spherical face. This sundial was then marked so that they more accurately predicted time throughout the year using a new math called geometry. This knowledge allowed the Greeks to invent the hemicycle. This invention consisted of a cubical block of wood or stone that was divided into hemisphere with a stick or rod that was attached to one end. The circular arc that was created varied in length depending on the season of the year. To get a more accurate reading, these arcs were then divided into twelve equal quadrants, which indicated the length of each day. An example of this is the Tower of Winds in Athens. This timepiece consists of eight sundials that face the cardinal points of the compass.
China had their version of the sundial called “Rigou.” This type of sundial was very popular during the Zhou Dynasty. Later on, more portable types of sundials were invented during the Song Dynasty.
There is more to sundials then measuring shadows throughout the season. A sundial is made of a base or faceplate that can be any shape. Attached to this faceplate is a gnomon or needle. As the sun hits the gnomon, it will cast a shadow upon the plate. The plate is then marked with time related measurements. These can consist of hourly time, seasonal time, shortest and longest days, and dates.
But since the sun rotates around the sun, the axis of the sun needs to be added to the sundial equation. Without taking into consideration the axis, the time calculated by the shadow will be different every week. To address the earth’s axis, one simply needs to line up the gnomon with the earth’s axis.
Types of Sundials
There are three types of sundials, which include horizontal, equatorial, and vertical. The horizontal type of sundial is set up so that the base is placed horizontal while the gnomon is tilted in line with the earth’s axis. The equatorial sundial, on the other hand, has its base placed at an angle that is parallel to the equator while the gnomon is placed perpendicular to the base. The vertical sundial is the most common and consists of a base that is placed vertical while the gnomon is aligned with the earth’s axis.
Another component of sundial placement is the hemisphere. The latitude that the sundial is placed in one hemisphere should be the opposite for the other hemisphere. To aid in this placement, set up the sundial according to the area’s true north or south, then adjust the axis by the longitude.
To enjoy a sundial in your own yard, browse Outdora’s wide selection of sundials. To please both bird watchers and add even more beauty to your backyard, there are also birdbath/sundial combos like the Hummingbird Sundial Birdbath Combination. Whatever type of sundial you choose, now know a little bit of history about the backyard accessory to wow friends and family.
ABOUT THE AUTHOR
Mindy McIntosh-Shetter has been an Agricultural Science educator, and is a horticulture and/or environmental blogger who earned a degree from Purdue University in Agriculture Education with a minor in biology, and natural resources. Presently she is finishing up her Masters in Environmental Education and Urban Planning for the University of Louisville while working on her own agriculture/environmental blog.