What is heliograph?

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What Does heliograph Mean

There are two types of devices called heliograph . On the one hand, it is called thus to a device used in the field of meteorology to estimate the intensity and extent of the exposure time . On the other hand, a heliograph is an element that produces telegraphic signals through the reflection of sunlight in a moving mirror.

In meteorology
Let's start by analyzing the heliograph as an instrument of the meteorological field. In this case, the heliograph allows us to analyze how intense the rays of the sun that reach a surface are and how long they last .

Measures the intensity and duration of the sun's rays

There are different kinds of heliographs. While some include clockwork mechanisms for their operation, others use the rotation of the planet Earth to calculate time .

The traditional heliograph consists of a crystal ball that concentrates the sunlight on a band that, when burned, generates a trace . This band is located at a constant distance from the focus of the sphere.
The duration of the insolation, in this way, is determined according to the length of the trace charred by the rays, provided that the sun has shone without pauses. When its brightness is not continuous, the extensions of the trace segments are added , which is intermittent.
Bands used by the heliograph
Depending on the time of year, three different kinds of bands are used . Next we will see its description taking as reference the northern hemisphere:
* straight bands : they are placed attached to the grooves in the center of the support. They are used from the beginning of March to the middle of April and from the beginning of September to the middle of October. Since they are located around the equinoxes, they are known by the name of equinoctial bands ;
* short curved bands : they are located in the grooves at the top. Its use takes place between the month of October and the end of February;
* Long curved bands : put in the grooves at the bottom. They are useful between April and August.
Settings for your installation
When the heliograph is supported on the support, it is necessary to pay attention to the following two points, for which it has reference marks:
* the cap must be positioned so that the middle line of the straight band is in the plane of the celestial equator (the projection of the equatorial line on the celestial sphere);

* The geographic meridian plane must coincide with the vertical plane on which the noon signal and the sphere are located.
In telecommunications
As for the heliograph as a communication tool, it is hardly used anymore because it was replaced by radio signals . Before technological advances, this device was useful for sending telegraphic signals, causing the sun's rays to be reflected in a movable mirror and thus emitting the signals even from one town to another.

Telegraph signals reflecting sunlight

Telegraph signals are electrical, that is, they are generated by means of electromagnetic phenomena . They can be digital or analog, depending on whether they vary discretely or continuously over time , respectively. In addition to the mirrors, a device similar to a blind used to be placed between them and the sunlight, so that their opening or closing movement allowed or prevented the passage of rays.
One of his weaknesses was that day could be used only because it depended solely on the light plot. In addition, this is linked to another of its main disadvantages: anyone outside the system could know if the operators were sending or receiving a message, since it was not easy to hide the mirrors.

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