Solar quadrant

Solar quadrant . It is an alteration of the word quadrant and designates the quarter circle where the height of a star is read above the horizon . Extensively, this word is applied to instruments that mark the time. The cuadrantessolares (gnomon in Greek) are watches sun in which the read time as the length of the shadow cast by the movement of the luminary on a given, same surface generally has a numbered scale to indicate time.


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  • 1 Description
  • 2 History
  • 3 Construction
  • 4 Sources


The principle of solar quadrants is based on the projection of the shadow of a rod (called style) on a graduated support. The Sun makes an apparent revolution every 24 hours (obviously it is the Earth that turns on itself). It is possible to measure the hour angle of the Sun and find the true solar time, or by the correction bias, the legal time.

Quadrants can be built on all types of flat supports or not. Non-flat quadrants are quite rare and difficult to build. The flat quadrants are as varied as the orientation and inclination of the support. The most common are the horizontal quadrants (often placed on columns in the gardens) and the southern vertical quadrants (on the facades of houses and in churches). The science of solar quadrants is called gnomonic, not to be confused with gnomics despite their common etymology.

A quadrant bears characteristic lines and inscriptions that have a precise meaning. Let’s look at this with an example of the southern vertical quadrant:

Lines and inscriptions of a solar quadrant

  • Straight lines are called time lines. They allow knowing the time from the shadow of the style. Some lines give hours (1), half hours (2) or quarter hours (3) or every five minutes.
  • Style (4) has two parts: the straight style placed at A and the polar style placed at B.
  • The line through these two points is called the substyle line (5).
  • The hourly line corresponding to solar noon is the line with the steepest slope (6). Corresponds to the intersection of the place meridian with the quadrant surface.
  • Depending on the season, the shade is more or less long and away from point B, depending on the declination of the sun.
  • Notable moments are marked as the solstices (7) and the equinoxes (8).
  • The other intermediate curves are the declination curves.

Apart from the aspect of the measurement of time (which in no way can compete with modern watches), the solar quadrant must be characterized by a graphic and original decoration. The quadrants brighten up the facades and gardens and some of them are true works of art.

The currencies or slogans that carry the dial gives them personality. In modern quadrants, they are less frequent in Latin but are always steeped in philosophy. They can come from a literary work or form a judgmental maxim.

The vertical quadrants are usually painted on facades. In the southern region of the Alps they are very abundant, and some are very well preserved or restored. The technique must ensure that they resist the outrages of time. More isolated to be made, the quadrants on wood or metal have the advantage of being able to be prepared in a different place from that of their installation. Quoi qu’il en soit, the solar quadrants are a source of artistic, scientific and historical pleasures. The Shadows program frees you from the mathematical aspect and allows you to focus on the artistic aspect.


The first Chaldean Quadrant dates, 2234 years BC The first Solar Quadrant was drawn in Rome by Messala, the year 276 of the same era. Solar quadrants were decisive in the measurement of time, especially from antiquity to the Renaissance , when clocks became widespread. In 2000 ], in the Place de la Concorde (Paris) , a gigantic solar quadrant was installed in which the obelisk served as a gnomon. But who had the idea was Camille Flammarion ( 1913 ), although the war prevented it on two occasions.

All civilizations, from Egypt to China , from Mexico to the Near East , knew the sundial. The first small solar quadrant that was known, among the Egyptians of the XV century before our era, was very simple: it consisted of a simple bar that nailed perpendicularly to the ground, forming a line parallel to the axis of the Earth. The length and position of the projected shadow allowed calculating the points corresponding to the passage from day to night, as well as the solstices. The hours of the day were marked on the ground surrounding the bar. The huge obelisks were also used for the purpose of measuring time from the shadow they created, so they were used as public clocks.

Solar quadrants are believed to have been in use in Greece from the 500s and the 2nd century BC . The use of the sundial or solarium became so common throughout the Roman Empire that it was admitted in legislation and all private businesses were regulated by the hours marked on the dial.

There were solar quadrants of many shapes: flat quadrants, cubic quadrants, hollow globes, sections of numbered steps on which the shadow of a vertical wall was projected, and portable compass quadrants. Introduced compass dials , introduced in the 15th century , were the first portable shadow watches that could be carried in your pocket. The compass was used to point the quadrant to the north and the gnomon (a piece of rope or a folding triangle ) was lowered or raised to accommodate the latitude at which the compass was used .


Positioning of a solar quadrant

“Solar quadrant” sundials are made up of a stylus, the shadow of which is cast on a plane or quadrant on which the time lines that allow us to determine the time are drawn.

By the orientation of the quadrant we can distinguish different types of sundials:

  • Equatorial quadrant: if it is parallel to a plane that cuts our planet through the equator.
  • Horizontal quadrant: if it is horizontal.
  • Of vertical oriented quadrant: it is vertical and oriented towards the South.
  • Decline vertical quadrant: it is vertical, but it is not oriented exactly to the South.
  • It is the typical sundial on the facade of a house .

An equatorial dial sundial can be easily constructed from cardboard or plywood. It consists of two pieces: a rectangular one that will be the quadrant and a triangular one that will serve as a stylet and support. Each of them has a slot, which allows us to fit them.

We will begin its construction by cutting out the quadrant, which is a rectangle twice as long as it is wide. Its dimensions may be as we wish, although it is recommended that it be 15 to 30 centimeters long. Halfway through the length, a slot should be made that reaches half the width, with the same width as the thickness of the material used for its construction (the line that appears in dashed lines in the figures).

The time lines must be drawn at 15º intervals on both sides of the quadrant: the spring – summer and autumn-winter faces . The traces in the figures are valid for a watch to be used in the northern hemisphere, for the southern hemisphere we will exchange the spring-summer for the autumn – winter .

To build the second piece, the stiletto, we must know the latitude of the place where our watch will be located. It is a right triangle where the angle must be equal to latitude, so that the quadrant is parallel to the equator, and the length of the segment is equal to that of the smaller side of the quadrant. A slot (the line that appears in dashed lines in the figure) must also be made in this piece that will allow it to be assembled with the first.

Once the two pieces are built and assembled, the watch should be placed in a horizontal position and correctly oriented. If the watch is to be used in the northern hemisphere, the spring-summer face should face north (as shown in the figure), while if it is to be worn in the southern hemisphere it will face south. To determine the North-South direction we can use a compass; Keep in mind that North does not coincide with the direction indicated by the needle, which points to Magnetic North. Another method is to use the shadow of a vertical object (a plumb line) at noon, indicating the North-South direction; It must be taken into account that it must be exactly 12 hours of true solar time, which does not coincide with the 12 hours of our clocks. What time does our sundial indicate?

In spring and summer the Sun falls on the upper face (that of spring-summer), where the shadow of the stylus will be seen. In autumn and winter the shadow of the stylus is cast on the lower face (the autumn-winter face), while the upper one remains in shadow.


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