Solar watch

Solar Clock . It was one of the few ways to measure time in antiquity, but it has not stopped being a useful and curious instrument. Nowadays it not only allows us to know the time and day of the year, but it is also used to know some characteristics of the Sun , even with the absence of solar radiation , and it contributes its aesthetic value. With a suitable design, the solar clock allows us to know, for example, the sunrise and sunset times for any day of the year; the duration of the day and night; at what time, according to the date, does direct solar radiation affect each wall according to its North , South , East or West orientation; and the position of the Sun at any time and day of the year, either by day or by night. It also allows orientation, since the solar clock indicates the position of the North Star .


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  • 1 Description
  • 2 Operation
  • 3 Examples
  • 4 Sources


The sundial can have different shapes, commonly on flat vertical, horizontal or inclined surfaces. A sundial can be made on curved and uneven surfaces, and even inside a closed restaurant or lounge. In the latter case, it would not be the shadow that would give the time, but a solar ray that would be allowed to enter the room.


Since one is child realizes that the shade of a tree, a pole or any object exposed to the sun, “walk”, that is, changes its position over time the same as a ray of light sun entering the house . It is also observed that lightning and shadows vary their trajectory with the time of year. In other words, while at the end of June , in Cuba , the Sun is above us at midday, at the end of December, also at noon, the Sun is inclined almost 45 °. This variation of the position of the Sun at noon, relative to the time of the year is called “declination of the Sun” and is due to the Earth’s axis of rotationit is inclined in relation to the plane of its translation around the Sun. This effect also depends on the distance of each country from the equator, that is, on its latitude.

It has long been known that the Earth makes a complete turn around the Sun every year and rotates around its axis of rotation called the polar axis, with constant speed. This rotation of the Earth makes it appear to its inhabitants that the Sun turns it every 24 hours or a solar day. Since a full turn means 360 °, each hour corresponds to a rotation angle of 15 °. Thus, the Earth’s surface is divided by meridians that define the 24 time zones; the so-called Greenwich Meridian is taken as the initial , so-called because it passes through the Greenwich Royal Observatory , east London. Each of these spindles corresponds to an angle of rotation of the Earth of 150, or 1 h, and in each of them the single reference time of the aforementioned universal or Greenwich meridian is taken, increased or decreased, as appropriate. , for an integer number of hours, keeping the same minutes and seconds.

Each country thus assumes, as “legal time”, the civil time of the spindle where it is located. The civil time of Cuba takes as reference the meridian 75 or meridian of Yateras , and passes through the province of Guantánamo . Actually, not every day of the year has the same duration, since the Earth rotates around the Sun with an elliptical and non-circular trajectory; in addition, the Sun is placed in one of its foci, so the distance between it and Earth varies with the year and because the Earth’s axis of rotation is not perpendicular to its plane of rotation around the Sun, called the plane of ecliptic. This name is given because in this plane the Sun , the Moon must coincideand Earth for eclipses to occur. For the reasons mentioned above, there is a difference between “civil time” (which assumes that all days are equal in duration) and “true time”. This difference is called the equation of time.

From what has been studied, it is understood that a solar clock provides the true solar time and that to bring it to the official time it is necessary to make the following correction: All the solar clocks have marked the time zones or lines that give the solar time, the one that is determined at every moment by the shadow, on the surface of the clock, of a rod called gnomon. Some watches also have the lines that determine the day of the year.


A very interesting sundial is the one built at the Solar Energy Research Center in Santiago de Cuba . This watch is characterized by being formed by a circular sector that allows you to see the time and day of the year by the shadow that the small sphere placed in the center casts on its surface. The sundial in Plaza Martiana , in Las Tunas , also built on a horizontal surface, is possibly one of those built in Cuba , the one with the most originality, since the Sun indicates, with its change in declination according to the day of the year, the most significant biographical events in the life of José Martí . But the most interesting element of this watch is that every May 19At half past two in the afternoon (time when the Apostle fell), the sunlight reflected by a mirror illuminates the countenance of the Master, recalling his desire to die facing the Sun.

There are thousands of examples of sundials around the world that are looked at with curiosity by the variety of their shapes and designs, one of them is the Ecuador Sundial , which remembers half the world.

The materials used for the construction of sundials can be many and varied, such as: metals , stones ( granite , marble , etc.), paintings and even ornamental plants that brighten up a garden due to the color of its leaves or flowers . The proliferation of sundials in cities, parks and buildings, in addition to brightening the surroundings, enrich the solar culture of the peoples.


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