A sundial is an early timekeeping device that indicates the time of day using the position of a shadow cast by the sun. The sun moves across the sky, causing the shadow of an object to move and display the passage of time. The sun shines on a gnomon , a device set perpendicular to a base plate, which casts a shadow on the appropriate hour line, displaying the time. The angle on the gnomon must be parallel to Earth’s axis and equal to the sundial's latitude for accurate time.

How does a sundial tell the time?

A sundial is an early timekeeping device that indicates the time of day by the position of the shadow of an object exposed to the Sun's rays. As the day progresses, the sun moves across the sky, causing the shadow to move and indicate the passage of time. The sun shines on a gnomon, which is a triangle or device set perpendicular to a base plate. The gnomon casts its shadow on the appropriate hour line, displaying the time of day. The angle on the gnomon has to be parallel to Earth’s axis and must be equal to the latitude of the sundial’s location if it is to display accurate clock time.

What are the main parts of a sundial?

A sundial is an early timekeeping device that indicates the time of day using the position of the shadow of an object exposed to the sun's rays. The main components of a sundial are: * Gnomon A vertical stick, pin, or pillar that casts a shadow. The angle on the gnomon must be parallel to the Earth’s axis and equal to the latitude of the sundial’s location to display accurate time. * Base Plate The base on which the shadow of the gnomon falls. * Hour Lines Markings on the base plate that correspond to the hours of the day.

Why does the position of the sun affect a sundial?

A sundial measures time by using the position of the Sun. As the Sun moves across the sky, it casts a shadow on the sundial's gnomon , which is a device that is set perpendicular to a base plate. The position of this shadow indicates the time of day. The angle of the sun's rays affects the intensity of solar energy. The angle changes depending on the latitude, time of year, and time of day. When the Sun has a lower elevation angle, the solar energy is less intense because it is spread out over a larger area.

How do you read the time on different types of sundials?

A sundial is an early timekeeping device that indicates the time of day by the shadow's position of an object exposed to the Sun's rays. The Sun's movement across the sky causes the object's shadow to move, displaying the passage of time. The Sun shines on a gnomon , which is a triangle or device set perpendicular to a base plate. The gnomon casts its shadow on the appropriate hour line, displaying the time of day. The angle on the gnomon must be parallel to Earth’s axis and equal to the sundial’s latitude for it to display accurate clock time.

How have sundials influenced the development of clocks and other timekeeping devices?

Sundials, the earliest timekeeping devices, have significantly influenced the development of clocks and other timekeeping methods. The first device to indicate time was likely the gnomon , dating back to 3500 BCE. By the Middle Ages, sundials were common in Europe for identifying midday. The advent of mechanical clocks in the early 14th century brought sundials with equal hours into general use in Europe. Until the 19th century, sundials were utilized to reset mechanical clocks.

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Diagram of a sundial labeled with its main parts: a circular dial plate marked with Roman numerals and hour lines, a raised triangular gnomon with a style casting a shadow to indicate the time, and an arc showing the sun's path across the sky.

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sundial

timekeeping device

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Aug. 31, 2026 •History

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What is a sundial?
A sundial is an early timekeeping device that indicates the time of day using the position of a shadow cast by the sun. The sun moves across the sky, causing the shadow of an object to move and display the passage of time.

The sun shines on a gnomon, a device set perpendicular to a base plate, which casts a shadow on the appropriate hour line, displaying the time. The angle on the gnomon must be parallel to Earth’s axis and equal to the sundial's latitude for accurate time.
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How does a sundial tell the time?
A sundial is an early timekeeping device that indicates the time of day by the position of the shadow of an object exposed to the Sun's rays. As the day progresses, the sun moves across the sky, causing the shadow to move and indicate the passage of time.

The sun shines on a gnomon, which is a triangle or device set perpendicular to a base plate. The gnomon casts its shadow on the appropriate hour line, displaying the time of day. The angle on the gnomon has to be parallel to Earth’s axis and must be equal to the latitude of the sundial’s location if it is to display accurate clock time.
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This answer is created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are the main parts of a sundial?
A sundial is an early timekeeping device that indicates the time of day using the position of the shadow of an object exposed to the sun's rays.

The main components of a sundial are:
* Gnomon A vertical stick, pin, or pillar that casts a shadow. The angle on the gnomon must be parallel to the Earth’s axis and equal to the latitude of the sundial’s location to display accurate time.
* Base Plate The base on which the shadow of the gnomon falls.
* Hour Lines Markings on the base plate that correspond to the hours of the day.
2 Britannica Sources
1. sundial
2. 22 Questions About Time and Timekeeping Answered: What is a sundial and how does it work?
This answer is created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why does the position of the sun affect a sundial?
A sundial measures time by using the position of the Sun. As the Sun moves across the sky, it casts a shadow on the sundial's gnomon, which is a device that is set perpendicular to a base plate. The position of this shadow indicates the time of day.

The angle of the sun's rays affects the intensity of solar energy. The angle changes depending on the latitude, time of year, and time of day. When the Sun has a lower elevation angle, the solar energy is less intense because it is spread out over a larger area.
3 Britannica Sources
This answer is created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do you read the time on different types of sundials?
A sundial is an early timekeeping device that indicates the time of day by the shadow's position of an object exposed to the Sun's rays. The Sun's movement across the sky causes the object's shadow to move, displaying the passage of time.

The Sun shines on a gnomon, which is a triangle or device set perpendicular to a base plate. The gnomon casts its shadow on the appropriate hour line, displaying the time of day. The angle on the gnomon must be parallel to Earth’s axis and equal to the sundial’s latitude for it to display accurate clock time.
2 Britannica Sources
1. sundial
2. 22 Questions About Time and Timekeeping Answered: What is a sundial and how does it work?
This answer is created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How have sundials influenced the development of clocks and other timekeeping devices?
Sundials, the earliest timekeeping devices, have significantly influenced the development of clocks and other timekeeping methods. The first device to indicate time was likely the gnomon, dating back to 3500 BCE. By the Middle Ages, sundials were common in Europe for identifying midday.

The advent of mechanical clocks in the early 14th century brought sundials with equal hours into general use in Europe. Until the 19th century, sundials were utilized to reset mechanical clocks.
2 Britannica Sources
1. sundial
2. 22 Questions About Time and Timekeeping Answered: When and how did the first modern clocks develop?
This answer is created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

sundial, the earliest type of timekeeping device, which indicates the time of day by the position of the shadow of some object exposed to the sun’s rays. As the day progresses, the sun moves across the sky, causing the shadow of the object to move and indicating the passage of time.

The first device for indicating the time of day was probably the gnomon, dating from about 3500 bce. It consisted of a vertical stick or pillar, and the length of the shadow it cast gave an indication of the time of day. By the 8th century bce more-precise devices were in use. The earliest known sundial still preserved is an Egyptian shadow clock of green schist dating at least from this period. The shadow clock consists of a straight base with a raised crosspiece at one end. The base, on which is inscribed a scale of six time divisions, is placed in an east-west direction with the crosspiece at the east end in the morning and at the west end in the afternoon. The shadow of the crosspiece on this base indicates the time. Clocks of this kind were still in use in modern times in parts of Egypt.

Another early device was the hemispherical sundial, or hemicycle, attributed to the Greek astronomer Aristarchus of Samos about 280 bce. Made of stone or wood, the instrument consisted of a cubical block into which a hemispherical opening was cut. To this block a pointer or style was fixed with one end at the centre of the hemispherical space. The path traveled by the tip of the pointer’s shadow during the day was, approximately, a circular arc. The length and position of the arc varied according to the seasons, so an appropriate number of arcs was inscribed on the internal surface of the hemisphere. Each arc was divided into 12 equal divisions, and each day, reckoned from sunrise to sunset, therefore had 12 equal intervals, or “hours.” Because the length of the day varied according to the season, these hours likewise varied in length from season to season and even from day to day and were consequently known as seasonal hours. Aristarchus’s sundial was widely used for many centuries and, according to the Arab astronomer al-Battānī (c. 858–929 ce), was still in use in Muslim countries during the 10th century. The Babylonian astronomer Berosus (flourished c. 290 bce) invented a variant of this sundial by cutting away the part of the spherical surface south of the circular arc traced by the shadow tip on the longest day of the year.

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The Greeks, with their geometrical prowess, developed and constructed sundials of considerable complexity. For instance, the Tower of the Winds in Athens, octagonal in shape and dating from about 100 bce, contains eight planar sundials facing various cardinal points of the compass. Moreover, numerous ancient Greek sundials feature conical surfaces cut into stone blocks in which the axis of the cone (which contains the tip of the gnomon) is parallel to the polar axis of Earth. In general, it appears that the Greeks constructed instruments with either vertical, horizontal, or inclined dials, indicating time in seasonal hours.

As with the Greeks, the Romans’ sundials employed seasonal hours. In 290 bce the first sundial, which had been captured from the Samnites, was set up in Rome; the first sundial actually designed for the city was not built until almost 164 bce. In his great work De architectura, the Roman architect and engineer Vitruvius (flourished 1st century bce) named many types of sundials, some of which were portable.

The medieval Muslims were especially interested in sundials, for these provided means for determining the proper times for prayer. Indeed, most Muslim sundials contain lines indicating these times, and on a few they are the only lines at all. Although the Muslims learned the basic principles of designing sundials from the Greeks, they increased the variety of designs available through the use of trigonometry. For example, they invented the now-ubiquitous sundial with the gnomon parallel to the polar axis of Earth. At the beginning of the 13th century ce, Abū al-Ḥasan al-Marrakushi wrote on the construction of hour lines on cylindrical, conical, and other types of sundials and is credited with introducing equal hours, at least for astronomical purposes.

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With the advent of mechanical clocks in the early 14th century, sundials with equal hours gradually came into general use in Europe, and until the 19th century sundials were still used to reset mechanical clocks.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Rick Livingston.