Sundial

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The Sundial is a device that tells time by using a flat surface and a long stick called a gnomon to turn the sun's reflection into a shadow that corresponds to a particular marking. The sundial was once used by many civilizations, including the likes of the Ancient Egyptians, the Babylonians, the Ancient Greeks, the Roman Empire, the Chinese, the Mayans, and the European countries during the Renaissance.

History

  • 5000-1500 BC: The first device to tell time was made; the simple model consisted of a pillar sprouting from the ground, similar to the later models of the sundial. Shadow clocks were also developed by Egyptian and Babylonian astronomers.
  • 800 BC: The earliest known sundial preserved came from this time period. The model had a base with six different time divisions inscribed, and a raised crosspiece that casted a shadow pointing to a division.
  • 560 BC: The Ancient Greeks develop the basic principles of the sundial, derived originally from Babylonian ideas. Since the Greeks founded geometry as well as the concept of conic sections, sundial construction came natural to them.
  • 400 BC: The Ancient Greeks begin using the water clock, which measures time by the outflow of water from a particular location..
  • 300 BC: Babylonian priest Berossus creates a sundial in the form of a half sphere cut into a large block. A small bead was placed at the center of the half sphere, and its shadow would move in a circular arc throughout the day. The arc was divided into 12 parts, each representing a different hour.
  • 263 BC: Around this time the sundial assumed the role as a constant unit of time. The first sundial was also imported to Rome from Sicily.
  • 100 BC: Astronomer Theodosius of Bithynia invents a universal sundial that can be used anywhere on Earth, regardless of its position relative to the sun.
  • 30-25 BC: Roman author Vitruvius outlines 13 different styles of the sundial.
  • 10 BC: The Romans build a very large sundial and call it the Solarium Augusti.
  • 150 AD: The Greeks use trigonometry to plot hours with a slanted gnomon.
  • 1200: Equal hours of the day are introduced relative to the sundial.
  • 1500-1800: Due in part to the spark of the Renaissance, European sundials become extremely popular as the main time-telling device.
  • 1700s AD: Clocks and watches begin to replace sundials since they do not require sunlight, but they are frequently inaccurate and must depend on sundials for exact times.
  • 1724: The Prince of Dials is placed in Old Delhi, it was the largest sundial in the world at the time. The sundial was so big that the shadow moved at a rate of five feet per minute.
  • 1777: French General Lafayette gives General and eventual President George Washington a silver Explorer Sundial as a gift of respect.
  • Early 1800s: Mechanical clocks become accurate and inexpensive enough to begin replacing sundials.

How the Sundial Works

The basic model of the sundial consists of a sloping face or flat surface that faces the sun directly. A gnomon (pronounced(no men) or a long stick/pole is attached to the base of this dial, usually near the middle, and the shadow of the gnomon falls on the dial. Also on the dial are markings that designate the hour of the day; where the shadow falls on the dial determines the hour. These markings usually take the form of parallel lines that range from top to bottom, sometimes also showing the different months of the year as well as the summer and winter solstices. Sundials were built and marked based on their position relative to the earth's axis; sundials were not portable past a small range until later because the position relative to the axis would be skewed if a sundial was moved a decent distance without being adjusted. The dial plate was usually made of light and refractory material, which was unalterable by heat or moisture in order to withstand outside weather conditions. Greek sundials tended to use bowl-shaped dials, with gnomons to tell time as well as seasonal information with the size of the shadow being indicative of the time of year. Placing the gnomon across a curved surface would indicate the summer and winter solstices and the equinoxes in fall and spring.

Different Types of Sundials

Religious

During the European Dark Ages Muslims used trigonometry to make flat circular sundials. These sundials were the first to propose hours of equal length, and they often marked the hours that Muslims prayed. This model also helped to record events on a schedule.

Horizontal

Known as the 'garden sundial', the horizontal model was found commonly on pedestals in gardens. The dial plate was horizontal, and the gnomon formed an angle equal to the latitude of the location. The plane was aligned horizontally to match the gnomon angle. This model was advantageous because it was easy to read, and because the sun would light the plane throughout the entire year.

Vertical

The vertical model was usually found on the walls of buildings because they were easy to read from far away. A common practice was to position vertical sundials on all four sides of a rectangular tower, so that time could be told throughout the day in four divisions. Vertical models were split up into two subdivisions. If the sundial faced south it was called a direct south dial, and the gnomon would have an angle aligned with the Earth's axis of rotation. Dials that faced north, east or west were called vertical direct, and had limited hours. If the dial faced east it could only tell time in the morning, as the sun would not shine down in its direction in the afternoon; thus the model with four sundials on a rectangular tower was put in use. Dials that faced north could only tell time before 6 AM and after 6 PM, and consequently it was the least used sundial. Vertical dials that faced east or west were called polar dials.

Equatorial

In this model the dial plate was in the plane relative to the equator, and the gnomon was perpendicular to the dial plate. This model also included an armillary sphere, which consisted of rings in the planes of the equator. The shadow was cast from below in the winter and from above in the summer. A drawback of this design was that no clear shadow was produced on the dial near the equinoxes in spring and fall, since the sun would move on a circle that was very similar to that of the equatorial plane.

Spherical

These models resembled a sphere, with the dial being a semicircle. They were popular in France to create and maintain train schedules prior to World War I.

Movable

Analemmatic Dial

This model was not common because the gnomon was vertical, and the hours were marked by points instead of lines. The gnomon had to be moved depending on the time of year. This dial was most commonly found laid out on lawns where a person could act as the gnomon.

Universal Equinoctial Ring Dial

Inspired by the astrolabe, this model also included the armillary sphere. The most portable of the sundial models, it contained a thin slit that allowed sun rays to fall on the hour lines of the ring after the user tilted the dial towards the true north.

Altitude Based Sundial

This model measured the height of the sun in the sky, instead of the shadow of the suns rays. The suns altitude is the same at times equally far from noon (ex: 8 AM and 4 PM) so the user had to make a judgment call to decide whether or not it was morning or afternoon.

==Death of the Sundial