Find a Sundial

Find a Sundial and... Show It To Us!

Since Man became aware about the periodic character of the day, the attempts to measure time have been systematic. Using the beat of the heart and by developing simple instruments, Man started to try to measure time.

At a certain point our human ancestors guessed the time of day by observing the sun's movement from morning until night. Sunrise and sunset required no calculation, mid day (or noon) was a little bit trickier, but the time between these three reference moments left them baffled.

Their observations showed them that shadows cast changed in length and moved throughout the day. After a while they understood that it would be easier to measure the passing of time by observing the change in shadow lengths than by observing the movement of the Sun directly. This was the birth of Sundials.

During History, sundials have evolved into many forms and are widely spread out European countries.

So we challenge you: Find a Sundial... and tell us about it.

Image gallery of the 2012 competition.

First at all, we want to thank all participants in this EAAE project their work and collaboration because without them it would not have been possible to do. It is true that participation has not been very high. Our expectations about participation were much higher than occurred.

When we launched this project on our website we thought that the subject of sundials was very attractive and that students might find it attractive because it is easy that most of them have seen one in your city, town, etc.

Our intention is to convoke the second edition next autumn. We will try to improve and correct as far as possible the previous call with the end that you find more attractive and easy to understand our proposal.

In any case, we want to emphasize that in this Competition works are FREE, this is, each participant can do and present your work as they want. The rules listed in the call are only for guidance to help participants in the work to be done.

Finally, before seeing the names of the winners in the two modalities (groups and individual), we want to invite and encourage to all you to participate with your students or individually in our next edition. We believe that working with sundials can bring varied knowledge to our students. On the other hand, we have so many sundials all over Europe!

Then we want to present the winners of the first edition of the EAAE Competition: Find a Sundial and ... Show it to us!

Groups Modality

First Classified

School: Liceo Sagrado Corazón de San Fernando, Cádiz (Spain).

Tutor Teacher: Juan Manuel Vargas León.

Students: Juan Jiménez de Reyna, Jesús Daneri Cruzado, Manuel Benítez Pérez.

Title of the Work: Castle San Romualdo’s Sundial.

Second Classified

School: Astronomical Observatory by Youth Center of Haskovo (Bulgaria).

Tutor Teacher: Yoanna Kokotanekova.

Students: Yovelina Vasileva Zinkova, Radostina Boykova Velevska, Ivana Dimitrova.

Title of the Work: Analemmatic (“human”) sundial.

Individual Modality

First Classified

Name: Zhasmina Kostadinova.

City: Varshets, Montana (Bulgaria) Student of the High School Ivan Vazov in Varshets.

Title of the Work: A sundial in the courtyard of my school.

Second Classified

In this modality the Competition organizers have considered appropriate to declare the second award desert.

To participate you have to make a previous registration. You have to fill up the registration form (Download) and send it to us.

The registration form should be send by email to the EAAE webmaster and to the project coordinator.

Participation can be either from schools in groups of three or four students who are coordinated by a teacher or individually. That is, people may also participate by themselves if they have found a sundial and they consider it interesting to show us.

The final works should be submitted to the project chairperson and webmaster until March 30, 2012 to be place on the webpage.

Works produced must be submitted in PDF or Word format and images with sufficient quality by ensuring that the document is not too heavy and avoid problems sending.

Both schools and individual persons participating will receive a PDF Participation Certificate when works are received by us.

Two prizes will be awarded for work submitted by groups and other two for the presented individually.

In both cases the first prize is a Diploma issued by the President of the EAAE and the continuity of work in a gallery of our website for a time to be determined. For groups that have worked under the supervision of a teacher at the school, the Diploma will be awarded to the school.

Papers that are selected in second place prizes will be the same as those that are the first, stating in the diplomas if they are finalists or semifinalists.

The competittion winners will be announced the second fortnight of April of 2012. Also from the organization to inform you that have been awarded, an email will be sent individually.

Picture 1: Horizontal sundial in Warsaw's Palace Lazienkrowski (Poland).
Picture 1: Horizontal sundial in Warsaw's Palace Lazienkrowski (Poland).

Babylonians and Egyptians built obelisks which moving shadows formed a kind of sundial, enabling citizens to divide the day in two parts by indicating noon.

The oldest known sundial was found in Egypt and dates from the time of Thutmose III, about 1,500 years BC. There were two strips of stone, one that did the needle and another where the hours were marked.

After this first known sundial, we must advance to the 750 BC to have references from another sundial, and is found in several Old Testament passages that describe a sundial, that of Ahaz. A biblical reference tells how Yahweh did the shadow go back ten degrees on the dial. However, we are sure that there were other much earlier among almost all peoples of antiquity, although there is no evidence so clear as in this case.

Moreover, the earliest description and design of a concave sundial is attributed to the Babylonian Berossus in the IV century BC.

Picture 1: Greek sundial III-II century BC.
Picture 1: Greek sundial III-II century BC.
Picture 2.
Picture 2.

With the Greeks, sundials are studied thoroughly and for the first time, the gnomon stops of being installed vertically and passes the correct position, parallel to the Earth's axis. They developed and constructed complex sundials using their knowledge of geometry.

The watch Greek is called "scaphoid" (bowl) and consisted of a block in which a cavity was emptied hemispheres, at whose end is fixed the needle bar serving.

Put the gnomon parallel to the direction Earth's axis allowed the clock signal throughout the year the hours of a constant duration, making measuring instruments, really. In the previous vertical needle had clocks where summer hours were different from those of winter (as we have already commented above). It should also be mentioned that the scaphoid were also the first sundial that measured time by the direction of the shadow and not, as heretofore, by its length.

In fact, almost all posterior cultures, at least, those who had direct or indirect contact with the Greeks used for their design sundials Greeks: the Romans, Arabs, Indians, Afghans and so on. The Greeks sundials used refinements like the orientation of the object that casts the shadow or gnomon, which did not have to be perpendicular to the ground, and the geometric shape of the surface on which the shadow cast, which did not have to be flat, and they got excellent precision for the time, precision of a few minutes that would not be surpassed for centuries.

In picture 2 we can see a splendid Greek sundial called Horologion or Tower of the Winds. It consists of an octagonal marble building oriented according to the cardinal points and topped with a conical dome. This building was entrusted to Andronicus Cirrus that he did in 50 BC. With the Roman domination the ancient Agora of Athens was too small for their duties and it was decided to build a new one to move their business activities of the city. This new place was endowed with this advanced sundial: the Horologion.

The Romans copied the Greek scaphoid, which he called hemispherium. The ancient Romans, from the scientific point of view, did not add anything new with regard to measuring time, continued to use sundials developed by the Greeks.

Pliny the Elder in his Natural History relates the history of the sundial that Emperor Augustus ordered to build in the Campus Martius, using an Egyptian obelisk of Pharaoh Psamtik II, called the Solar Clock Augustus or Augustus Meridian.

Picture 3: Drawing of the Augustus meridian can be seen in the Champ de Mars, close where the sundial was.
Picture 3: Drawing of the Augustus meridian can be seen in the Champ de Mars, close where the sundial was.
Picture 4: The Agrippa Pantheon in Rome. The hole in the roof acts as a sundial (I century BC).
Picture 4: The Agrippa Pantheon in Rome. The hole in the roof acts as a sundial (I century BC).

On the astronomical content found in the architecture of the Pantheon in Rome, built by Agrippa in the first century BC, there is no doubt. But now some researchers argue that the Roman building acts as a huge sundial (Picture 4).

According to Roman architect and engineer Vitruvius, were used at least thirteen different types of sundials. Vitruvius wrote a book about gnomonics in which he describes a geometric method for designing sundials called analemma.

The Roman Empire's decline and fall because of the barbarian invasions, led in Occident a long period of intellectual darkness.

In the early centuries of the Christian era, the gnomonic, dimly lighted by studies of Hellenistic astronomy is entering a decline that characterizes the entire science of European medieval cultural and economic. There are few items (mostly archaeological) we can find; there are just written to show further progress. Although in this period to the general public cared little time measurement, there are no precise scientific descriptions. However, as oddities at the time, there were two surveyors: the Venerable Bede and Higinio Gromat (II century).

You need to wait until feudalism assist the dissemination of sundials on the European continent. It was the religious order Benedictine (529 AD) and his dedication to comply with the schedule dictated by its founder, what encouraged these monks to study the construction of sundials.

Since its origin, the Catholic Church wanted to sanctify certain times of the day with a common prayer. The gnomonic of these centuries led to the construction of Mass clocks or watches of canonical hours and in them the hours of prayer were indicated. These watches are generally located in the southern facades of churches or monasteries.

Picture 5: Sundial on the south facade of stone in the church of Revilla (Huesca, Spain).
Picture 5: Sundial on the south facade of stone in the church of Revilla (Huesca, Spain).

First sundials carved on the stone facades of churches and cathedrals are starting to appear early VIII century. In the year 1000 horizontal sundials were constructed for which holes were used in the vaults of cathedrals.

In the IX century Arabic astronomy comes in. The caliphate of Al Mamun marks the beginning of an intense cultural activity would continue in later centuries with writers such as Averroes, Ibn Thabit Qurraa (826-901) and Al-Biruni (973-1048) as example. While Christian Europe at the time followed the works of the Venerable Bede, the Arabs had a hectic continued intellectual activity from the destruction of the Alexandria Library. It is only from the X century when Europe begins to look timidly vast compilation of ancient knowledge work done by the Arabs.

The majority of Arabs watches were flat at that medieval times, constructed of marble or copper plates. They all have an indication of the direction of the Kaaba in Mecca because of the religious precept of praying with the face turned to that place regardless of where they are located.

Picture 6: Sundial at the Sidi Okba Mosque in Kairouan (Tunisia).
Picture 6: Sundial at the Sidi Okba Mosque in Kairouan (Tunisia).
Picture 7: Sundial at the garden of Topkapi Palace in Istanbul (Turkey).
Picture 7: Sundial at the garden of Topkapi Palace in Istanbul (Turkey).

The XI century, a German mathematician who knows the Arabic language, wrote a treatise on the astrolabe retaining some Arabic terminology. In this treaty are some indications for the shepherd's sundial. The translation of two Arabic manuscripts gnomonic was most important cultural advance of the time in this field.

Picture 8: Cathedral of Teruel. Two sundials, one south facing and one west. Teruel Cathedral began to be built in the Romanesque style in 1171 and concluded with the establishment of the Moorish tower in 1257. It is one of the most characteristic Moorish buildings in Spain.
Picture 8: Cathedral of Teruel. Two sundials, one south facing and one west. Teruel Cathedral began to be built in the Romanesque style in 1171 and concluded with the establishment of the Moorish tower in 1257. It is one of the most characteristic Moorish buildings in Spain.
Picture 9: Sundials of the Terual Cathedral; in the south facing right and the left of the west face.
Picture 9: Sundials of the Terual Cathedral; in the south facing right and the left of the west face.

In the XIII century in Spain, King of Castile Alfonso X the Wise put together in the city of Toledo a large group of Christians, Greek, Hebrew and Arabic astronomers to translate into Latin many of the works written in Arabic. Thus the Arabic knowledge spread throughout Europe to leave behind all the cultural obscurantism in which it was immersed. Also the gnomonic was developed, like all sciences.

In the XIV century, the first mechanical clock is made. It is a large iron-framed structure, driven by weights. The function of the first European clocks was not to indicate the time on a dial, but to drive dials that give astronomical indications, and to sound the hour. They are located in monasteries and public bell towers. The earliest surviving example, constructed in 1386, is in Salisbury Cathedral, England. Mechanical clocks utilize equal hours.

In Spain during the reign of Enrique III, in 1400, the first mechanical watch with bells was installed in the tower of the church of Santa Maria de Sevilla.

The following centuries were the great age of the European sundial. In the XV century a great effort was made in Europe by the divulgation of the Gnomonic. Sundials with equal hours gradually come into use.

In the American colonies were built many sundials, some of which are still preserved. In the tropics you have to build a double disc with time. The south-facing disk is used for part of the year, from August to April, and the disk on the other side facing north would use the rest of the year. Two days a year, when the Sun passes directly above the site hours can be seen on both sides.

By the mid-XVI century the first mechanical clocks appear. It is in the XVII when these devices are refined and slowly getting more accurate operation.

The onset of the Renaissance saw an explosion of new designs. Giovanni Padovani published a treatise on the sundial in 1570, in which he included instructions for the manufacture and laying out of mural (vertical) and horizontal sundials. Also, Giuseppe Biancani published (1620) other treatise where discusses how to make a perfect sundial with accompanying illustrations.

In the XVIII century clocks and watches begin to replace sundials. They have advantage of not requiring sunny skies. There are, however, often unreliable and depend upon sundials to set the true time.

In the early 1800’s mechanical clocks become accurate enough and inexpensive to displace sundials as timepiece of choice.

At present, although the accuracy of mechanical clocks outweighed sundials, they continue be built, primarily as a decoration on buildings, monuments and public places. They are constructed of many types with precision and beautiful designs. The support of the computer to calculation and design of the sundial has been fundamental. As a result of this technological support, are living the revival of this ancient instrument for measuring time in recent years, but as mentioned above, its function is currently not precisely what sundial was born but only as a decoration.

In any case, I welcome the resurgence of the sundial!!

Picture 10: Modern equatorial sundial in Tarragona (Spain).
Picture 10: Modern equatorial sundial in Tarragona (Spain).
Picture 11: Vertical sundial faced to the west a private house in Grañen, Huesca (Spain).
Picture 11: Vertical sundial faced to the west a private house in Grañen, Huesca (Spain).

Sundials indicate the local solar time, unless otherwise corrected. To obtain the standard clock time, three types of corrections need to be made.

First, the solar time needs to be corrected for the longitude of the sundial relative to the longitude at which the official time zone is defined.

For example, a sundial located west of Greenwich meridian, Saragossa or Madrid for instance, but within the same time-zone, shows a time before the official time determined by the meridian; it will show "noon" after the official noon has passed, since the Sun passes overhead later, since the sundial is further in the west. This correction is often made by rotating the hour-lines by an angle equaling the difference in longitudes.

Second, the practice of daylight saving time shifts the official time away from solar time by an hour or, in other cases as Spain, by two. This correction can be made by numbering the hour-lines with two sets of numbers (but it is not usual).

Third, the orbit of the Earth is not perfectly circular and its rotational axis not perfectly perpendicular to its orbit, which together produce small variations in the sundial time throughout the year. This correction, which may vary approximately from -16 minutes to +16 minutes, is described by the so-called “equation of time E”. The equation of time is formally defined as the difference between mean solar time and true solar time. This is due to the fact that the Earth moving around the Sun verified the law of areas, resulting a non-uniform motion which mechanical watches cannot fit exactly. So the real Sun sometimes outstrip the average Sun (or theory Sun for mechanical watches) and sometimes the opposite occurs. This correction, the equation of time, appears tabulated in astronomical annual.

So in response to the above, to determine the official time reading a sundial we must apply the following formula

Official Time = Sundial Time + E ± L + (1 or 2) hours

where E is the equation of time, L the longitude of the place (taking sign - if it is to the east and taking the sign + if the west), and add 1 hour if it rules the winter time or 2 if the summer (in Spain).

A more sophisticated sundial design is required to incorporate this correction automatically; alternatively, a small plaque can be affixed to the sundial giving the offsets at various times of the year. The marker of the sundial, the gnomon is set parallel to the Earth's axis and pointing at the celestial pole. Its angle therefore depends on the latitude. The shadow of the gnomon falls on a dial, allowing the time can be read off.

A sundial is in essence simply any form of stick - known as a style or gnomon - which casts a shadow. The position of the shadow can then be used to determine the current solar time.

A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the Sun casts a shadow from the gnomon, which is a thin rod straight edge, onto a flat surface marked with lines indicating the hours of the day. The shadow cast by the end of the gnomon is the solar time at all times. As the Sun moves across the sky, the shadow of the gnomon's edge progressively aligns with different hour-lines on the plate. Such designs rely on the gnomon that is aligned with the Earth's rotation axis. Hence, if such a sundial is to tell the correct time, the gnomon must point towards the true North and the gnomon's angle with the horizontal plane must be equal to the geographical latitude where the sundial is placed.

The installation of many dials requires knowing the local latitude, the precise vertical direction (e.g., by a level or plumb-bob), and the direction to true North.

During the day people saw that the shadow cast by a tree, a rock, or even their own body was long early in the morning and grew shorter and shorter until it almost disappeared when the Sun was in the middle of the day. They also would have noticed that the shadow grew longer again, on the other side of the tree, as night came.

The shadow stick is the earliest form of sundial. People judged the time of day by the length and position of the stick's shadow.

As the Earth turns on its axis, the Sun appears to move across the sky. The shadows the Sun casts move in a clockwise direction for objects in the northern hemisphere. If the Sun rose and set at the same time and spot on the horizon each day, sticks would have been accurate clocks. However, the Earth is always spinning like a top. It spins around an imaginary line called its axis. The axis runs through the center of the Earth from the North Pole to the South Pole. The Earth's axis is always tilted at the same angle.

Every 24 hours the Earth makes one complete turn, or rotation. The Earth rotates on its axis from west to east. The Earth's rotation causes day and night.

On the Earth's yearly trip around the Sun the North Pole is tilted toward the Sun for six months and away from the Sun for six months. This means the shadows cast by the Sun change from day to day.

Because the Earth is almost spherical, the ground at the base of a shadow stick will not be at the same angle to the Sun's rays as at the equator. Because of this, the shadow stick will not move at a uniform rate during the day.

Picture 1: Equatorial sundial at the Imperial Canal of Aragon passing through Saragossa (Spain).
Picture 1: Equatorial sundial at the Imperial Canal of Aragon passing through Saragossa (Spain).
Picture 2: Horizontal sundial in Perdiguera, Saragossa (Spain).
Picture 2: Horizontal sundial in Perdiguera, Saragossa (Spain).

Eventually man discovered that slanting the gnomon and aiming it North made a more accurate sundial. Because its angle makes up for the tilt of the Earth, the hour marks remained the same all year long. After this discovery, people were able to construct sundials that were much better at keeping accurate time.

In the sundial of picture 1 we can see that the arrow replaces the gnomon or stick and is parallel to the axis of the world. The arrowhead points to the North Pole. There are various types of sundials. The picture 1 is the equatorial type since the gnomon projects shadows on a plane parallel to Equator.

Time “keeping” is simply a matter of counting cycles or units of time. A clock is what does the counting. In a more strict definition, a clock also keeps track of its count and displays what it has counted. In a broad sense, the Earth and the Sun are a clock -the commonest and most ancient clock we have, and the basis of all other clocks.

A sundial is a clock and human beings since antiquity has required timing. Among the most fascinating remains of many ancient civilizations are their elaborate time-watching devices. Great stone structures like Stonehenge, in Southern England and the 4000 year old grave of Newgrange, near Dublin, Ireland, that have challenged anthropologists and archaeologists for centuries, have proved to be observatories for watching the movement of heavenly bodies. Antedating writing within the culture, often by centuries, these crude clocks were developed by primitive peoples on all parts of the world. Maya and Aztec cultures developed elaborate calendars in Central and North America. Scientists even today find new evidence that some stones laid out in formation and that formerly thought to had only a religious significance, also, for the cycles of life -the rise and fall of the tides, and the coming an going of the seasons- powers that literally controlled the lives of primitive peoples as they do our own, naturally evoked a sense of mystery and inspired awe and worship.

Astronomy and time -so obviously beyond the influence or control of man, so obviously much older than anything the oldest man in the tribe could remember and as nearly "eternal" as anything the human mind can comprehend- were of great concern to ancient peoples everywhere.

When ancient peoples put a stick in the ground to observe the movement of its shadow from sunrise to sunset, it was fairly easy and certainly a natural step to mark off “noon” and other points where the shadow lays at other times of day –in other words, to make a sundial. Sundials can tell the time quite reliably when the Sun is shining. But, of course, they are of no use at all when the Sun is not shining. So people make mechanical devices called clocks to interpolate or keep track of time between checks with the Sun. The Sun is a sort of “master clock” that served as primary time scale by which the man-made, secondary clocks were calibrated and adjusted.

The sundial is the oldest known device for the measurement of time and the most ancient of scientific instruments. It is based on the fact that the shadow of an object moves from one side of the object to the other as the Sun “moves” from east to west during the day.

Picture 1: Visiting the Stonehenge monument.
Picture 1: Visiting the Stonehenge monument.

We propose in this page a simple competition for all students in Europe.

In many European towns and cities, walking the streets, we find sundials of various shapes and sizes. Some are old and they were built to be used as a way of measuring time. In many cases the only one available. Others, more modern, are built in prominent places as pure ornament and we can also find sundials in private houses and gardens.

Sometimes we come to small towns lost in the landscape and in the tower of the church or in any manor we find a sundial discolored and damaged by the passage of time. A broken clock but accurate enough.

In our opinion, these sundials that can be found throughout Europe and that some were built in the Middle Ages are part of the European Cultural Heritage.

Picture 1: Church of St. Felix in Revilla, Huesca (Spain).
Picture 1: Church of St. Felix in Revilla, Huesca (Spain).
Picture 2: Vertical sundial in the Church of St. Felix in Revilla, Huesca (Spain).
Picture 2: Vertical sundial in the Church of St. Felix in Revilla, Huesca (Spain).

As it is well know, one of the aims of the EAAE is the knowledge and diffusion of the common culture of a branch of science, Astronomy, which by its interdisciplinary approach allows us to manage other cultural areas where we find again common European contents as in History, Art, Philosophy and Science in general.

Therefore, this competition aims to "rescue" these sundials spread throughout Europe to be known by the public.

So to participate in the competition is only necessary to find a sundial, photograph and study it in the way that it is outlined in the following sections.

The competition is open to any student who wants to participate both individually and in groups of no more than three or four students from school.

Attention to this information

- The registration for participation in Find a Sundial and... Show It To Us competition may take place from September 1st of 2011 to March 30th, 2012.

- The deadline to send the work done to participate is the March 30th, 2012.

- The work shall be mailed to both the project chairperson and webmaster within the period specified.

- The competition winners will be announced the second fortnight of April of 2012 by email to the winners and on our website.