“The oldest system of counting time among the East Slavic tribes, whose economy was based on agricultural production, most likely was counting by seasons: spring, summer, autumn, winter. The complete period of changing seasons was called "summer". Weather records in Russian chronicles began with the words “in the summer,” which means “in a year.” Many ritual pagan holidays, which later became Christian, were associated with the agricultural calendar and the seasons. These are, for example, Maslenitsa, Kolyada (from the Latin “calendar”; another name for this holiday is “oat” – from “o-spring”), which celebrated the turning of the sun into summer, “red hill” – the holiday of welcoming spring, “rainbow” and "Rusalia" – spring and summer memorial holidays and others. Kolyada is a pre-Christian cycle of holidays among the Slavs during the winter solstice. According to ancient views, this is the beginning of a new life, renewal of nature, and therefore the beginning of a new year. Kolyada is accompanied by carols (songs and rituals). In the content of carols and their analogue in Ukraine and Belarus – shchedrivok – researchers identify more than 80 motives, the main ones being: good wishes, glorification and incantation. After the introduction of Christianity, the church included it in its Christmas and Epiphany cycles from December 24 to January 19 (the time of Christmastide – that is, increasing daylight hours). The church contrasted the games and rituals of carols with “glorifying Christ,” walking with a star and other Christian paraphernalia. As a result, a syncretic (mixed) ritual occurred. An inextricable connection with nature is shown by the ancient Russian names of the months: January was called Prosinets (the light part of the day noticeably increased, it became lighter), February – Sechen (this name reflected the practice of slash farming, it was the time of deforestation), March – dry (cut down trees dried out, and in some places the earth), April – birch or birch zol (the beginning of birch flowering in the southern regions, the transformation of burned trees into ash), May – grass (the time of the appearance of grass), June – isok (grasshopper), July – cherven or serpen ( harvest time), August – dawn (from "roar" – probably the beginning of the roar of deer during the autumn rut), September – ryuen (from the verb "ryut" – roar) or veresen (most likely from heather, juniper, blooming in autumn), October – leaf fall, November and December were called gruden ("gruda" – frozen road track), less often – jelly. Together with Christianity, the Julian calendar and Roman names of the months, recorded in one of the oldest monuments of Russian writing – the Ostromir Gospel, spread to Rus'. Many ancient Russian names of months have been preserved in the Ukrainian and Belarusian languages. In Ancient Rus', it was known to count time in weeks, seven days each. This is where the Old Russian name for the week “week” comes from. Unlike many ancient calendars, in which the days of the week were named after the planets dedicated to the ancient gods – Mars, Mercury, Jupiter, Venus, Saturn, the ancient Russian names of the days reflected their ordinal position relative to Sunday, which was called "week" (from "not to do" – do not work, as it was a day of rest). The next day is Monday (after the week), then Tuesday (second after the week), Wednesday (middle, middle of the week), Thursday (fourth), Friday (fifth day after the “week”). Saturday (in Slavic “six” or “six”) got its name from the Hebrew word “sabbath” (Sabbath), meaning rest. The modern Russian expression “six” is also associated with this same day of the week, meaning “incorrect”, “uncertain”, “two-faced”, since the Slavic name of the day of the week was not preserved, but, in fact, the well-known word “Saturday” was forcibly applied to us. Sunday (Resurrection) – a weekly Christian holiday established in honor of the resurrection of Jesus Christ, became the name of the day of the week in Rus.
The seven-day week dates back to Chaldean-Babylonian astronomical calculations; it was borrowed by the ancient Jews, who celebrated Saturday as a holiday in honor of the end of the divine creation of the world. Saturday was also celebrated in early Christianity; after dissociating themselves from Judaism, Christians began to celebrate the first day of the week, on which the resurrection of Christ took place, as a holiday. Survival names of the days of the week associated with astral cults have survived in some European countries to this day, for example: German Montag, English Monday – day of the moon (Monday), Sonntag, Sunday – day of the sun (Sunday), French Vendredi – day of Venus (Friday), English-Saturday – Saturn day (Saturday) and other words.