The word “heliograph” means “writing the sun” in Greek.
Currently, there are two types of instruments bearing this name:
– A meteorological instrument for measuring the duration of sunlight;
– signal apparatus, which is a type of optical telegraph.
Both devices are simple enough and have existed for a long time, despite this, have not lost their relevance.
Heliograph in meteorology
A simple but effective device for measuring the duration of the Sun’s presence in the sky is used by all weather stations around the world. The device looks exquisite: a sphere of clear glass, which is a lens to collect the sun’s rays, is fixed on an arc-shaped stand.
When the sun’s rays hit the ball, they bend as they pass through the glass, gathering at one point – the focus of the lens. There is a special light-sensitive strip with divisions.
As the sun moves across the sky, a beam of rays focused on the strip moves as well and burns a stripe on it. If clouds cover the sky, the rays disappear and the scorched strip is interrupted. The ribbon has a time grid with divisions of 0.5 and 1 hour.
By the end of the daylight hours, meteorologists have at their disposal a complete record of passaging the sun, from which they can determine how much time during that day was clear weather and how much was cloudy.
In order to get an accurate result, the heliograph is first oriented according to the directions of the world, and the side panel is set according to the latitude of the point where the observation site is located. The heliograph stand must be precisely aligned horizontally and must not have any irregularities on its surface.
The recording tape of the heliograph must be replaced exactly at 8 a.m. and 8 p.m. local time. In addition, the instrument is set up for morning and evening recordings and for work in wintertime or for high-latitude observations.
Heliograph is very useful for meteorologists to collect and accumulate statistical data, which, after processing and analysis, allows them to make short-term and long-term forecasts.
Light-signal heliograph
A device called a light-signal heliograph, or solar telegraph, before the invention of the radio was used to transmit brief messages of information over long distances. The oscillations of a mirror reflecting the sun’s rays were encoded especially, like Morse code.
Today, the need for such a device arises for people in distress and lost in the woods, in mountainous and rugged terrain. On a sunny day, the heliograph can signal to a passing rescue plane, reducing the search time.
A light-signal heliograph is a very simple device comprising two steel plates connected in the manner of a book or notebook. One of them is polished to a mirror shine, in the other, with a matte surface, a small hole is made in the middle (about 2-3 mm).
In order to give a signal, the heliograph flaps are pushed apart as far as they will go, the mirror flap is placed in front of the sun and the sighting hole is caught by an aircraft flying by, then the mirror flap is tilted to align the reflected sunbeam with the hole. The bright flash is clearly visible to the observer at a distance of several kilometers.
If you are when you need to send a signal for help, a heliograph can be made yourself from improvised materials. It suffices to pick up a small mirror and connect it at an angle of 60-70 degrees to a plate or plank, which in advance makes a small hole.
Because signaling with a heliograph requires some skill, you should first practice by sending the beam at tree trunks, distant rocks, or other objects.