Observing during the day the movement of the sun in the sky, a man from ancient times tried to find an explanation for this. Dependence on the luminary in the definition of time, in the organization of economic and everyday life generated an attitude towards him as a deity.
Myths about a chariot of fire making a daily journey through the sky are reflected in the cultures of many peoples. It is logical that the culmination of this procession - the moment when the position of the sun in the sky is the highest, formed the basis for the countdown.
Noon
The fact that it is not the Sun that revolves around the Earth, but rather, it became completely clear only by the middle of the 16th century. Moreover, one of the people who expressed this idea (Copernicus) was so sure that it contradicts the obvious - that you can observe daily that he prefaced his publication on the heliocentric system with words about its obvious absurdity.
Now the student knows that in fact the movement of the solar disk in the sky is the result of the rotation of the Earth around its axis, that our planet makes one full revolution per day, that the position of the sun above the horizon at a particular time depends not only on the angle of rotation to the star. It is affected by the position occupied by the Earth during its annual revolution around the Sun. In winter, in the northern hemisphere, our sun rises at noon lower than in summer.
Zenith
In order to accurately determine when the position of the sun in the sky is the highest, it is important to understand how this position is measured. If the highest point of passage of the center of the solar disk at noon is located exactly above the head (then the pole, stuck in the ground strictly vertically, casts a zero shadow), then the observer is at the equator.
In the Northern Hemisphere, the zenith point - the largest declination angle of the body relative to the horizon during the day, or the position of the sun at noon - is shifting to the north, in the Southern Hemisphere it is shifting downward in a southerly direction during the year. The main reason for the annual change in the height of the sun above the horizon at noon is the inclination of the axis of rotation of the globe to the plane of the orbit. It is constant and equal to 23.5 °.
Winter and summer
This slope also explains the change of seasons on our planet. The starting points for the onset of astronomical winter or summer are the solstice. In the Northern Hemisphere, the summer solstice is June 21 and 22. It is on this day that the sun is above all in the sky. The angle of incidence of sunlight on the surface of the planet is such that it heats up best. Large masses of water and earth gradually warm up and air temperature rises. The northern hemisphere is facing the sun at this time.
In the winter, December 21 and 22, north of the equator at noon, when the position of the sun in the sky is the highest, it rises above the horizon to a minimum height, if we take a change in this indicator during the year. At the same time, our area of the earth’s surface is deployed away from the main star of the solar system, receiving the least amount of beneficial heat. In the Southern Hemisphere, everything happens exactly the opposite.
True (astronomical) time
The appearance of time units such as year, month, and day is associated with astronomical observations and is directly dependent on the interaction between a single inhabited planet and a central star. The division into hours, minutes and seconds is arbitrary. The main factor for the appearance of just such numbers is the six-decimal number system, which was traditional for Ancient Babylon - it is from there that modern time units come from.
The period that passes between the moments when the position of the sun in the sky is the highest - what is called the day - is not constant throughout the year. The oscillation of this difference reaches 30 minutes and is explained by the elliptical shape of the orbit along which the Earth moves around the star. If true time were used in practice, one would have to create watches with an uneven course. Technically, this is now possible, but it is precisely in our time, when high accuracy of synchronization of events occurring in different regions of the planet is required, such a system seems especially impractical.
Average time
In order to offset the annual difference in the duration of the astronomical day, astronomers introduced the so-called "average Sun". This purely theoretical concept denotes a point that determines the position of our luminary in the sky, the movement of which is uniform for 365 days. Twice a year, its position coincides with the center of the real Sun. This occurs on the days of the spring and autumn equinox.
The introduction of the “average Sun” has led to the use of a more convenient average time in practice, otherwise called civil. This means that on a day different from the equinox days, the twelfth beat of the clock at noon does not mean the time of day when the position of the sun is highest. To calculate such a moment with an accuracy of fractions of a second, use the "equation of time", which contains data derived from the geographical coordinates of a particular place.