Calendar from Lat. calendarium, literally – a debt book (debtors paid interest on the 1st day of each month – a system for counting long periods of time, using the periodicity of natural phenomena, manifested especially clearly in the movements of the celestial bodies. The development of calendars reflects the conditions of the economic structure of peoples. Based on rich ethnographic material one can trace how identical forms of economic structure lead to the formation of similar calendar concepts. All nationalities have the concept of the year; the year is divided into seasons, the number of which is most often four, but can reach up to seven. Seasons are divided into smaller intervals (from 10 to 12 per year), having a connection with the lunar months. “The names of the months reflect the economic basis of life, for example, among the Siberian Evenki reindeer herders there is a month “when the deer peels the skin from the horns”, the month of “calving” and etc.; among the Tungus from the banks of the Amur there is a month of “arrival of chum salmon”, a month of “spawning.” Observations of luminaries have an undoubted connection with the calculation of time; The Nanais have a month “when the Bear’s head sets before dawn.” In tropical countries, a double cycle of field work (2 sowings and 2 harvests) coincides with a certain position in the sky of the constellation Orion; in other countries the Pleiades play an equally important role" (Great Soviet Encyclopedia, edited by B. A. Vvedensky, Moscow, 1953, vol. 19, p. 402). The first recorded physical calendars, dependent on the development of writing in the Ancient Near East, are the Bronze Age Egyptian and Sumerian calendars. The Ancient Egyptian calendar, associated with the visible annual movement of the Sun, is the prototype of all solar calendars. It was created back in the 4th millennium BC. e. for the purpose of regulating field work. It is known that around 2800 BC. e. the basic unit of time was the year; it was divided into 3 seasons (flood, winter and sowing, harvest) of 4 months each. The month was divided into 3 decades, that is, it had 30 days. After 12 months, 5 additional days were inserted into the calendar. Thus, all years had the same length of 365 days. The beginning of the calendar year was recorded on the day of the first visible (or heliacal, occurring against the background of dawn) rising of Sirius (Canis Major).