/ Astronomy

We have grown up planning our lives, our schedules, around the seven days of a week. For most of us, Monday to Friday are hustle-bustle days, then Friday night seems like a party night, and then come Saturday and Sunday, and there begins a lazy weekend. But ever wondered why this cycle repeats over exactly 7 days? Why not 6 or 8? Why does our weekly routine consist of 7 days only, who made these rules, and why and how was a week carved?

Our idea of a week
Our idea of a week

A day and a year

Our Earth takes roughly 24 hours (23 hours 56 minutes to be exact) to have a complete rotation around its axis, and this is what our duration of a day corresponds to. Furthermore, we complete one revolution around Sun in approximately 365 days (again 365 days, 5 hours, 59 minutes, and 16 seconds to be exact), and this is what our perception of a year refers to. Almost all our perceptions of various measures have an astronomical significance associated with them. So there’s an obvious reason to believe that the concept of a 7-day long week should also have some astronomical connection.

The motion of sun, earth and moon defines our idea of a year, month, day and even a week.
The motion of the Sun, Earth, and Moon defines our idea of a year, month, day, and even a week.

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The origin of the concept of 7 days in a week

Cosmic phenomena have always guided humanity in different ways. In ancient times, some civilizations were avid sky gazers, and one such civilization was that of Babylonians, an ancient society whose people lived in Mesopotamia (present-day Iraq). While observing the cosmic wonders, Babylonians came up with their original calendar that demonstrated the moon’s movement. The calendar also intended to exhibit the moon’s transition between phases: from full to waning half to new and eventually to waxing half.

Where Earth and Sun helped to identify days and years, the whole lunar cycle brought the idea of months to our platter. The moon takes approximately 28 days (plus 1 or 2-day arrangement) to go through the 4 phases, and this roughly equates to our idea of a month. Moreover, the time it takes to shuffle between these phases is approximately equal to 7 days, and here came the idea of having a week that is 7 days long.

Moon cycle
Moon cycle

Apart from this, there are several other stories as well behind the 7 days week duration. The Babylonians weren’t only curious astronomers but were also known for their hold in astrology. It is said that Babylonians curated a horoscope where each day of the week was assigned to one of the classical planets. The classical planets are the seven non-fixed celestial bodies that are visible to the naked eye. These include the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Of course, it isn’t right to call the Sun and the Moon planets.

Ever Wondered Why a Week Consists of Exactly 7 Days? 1
The 7 classical planets (Image: dribble.com)

The Babylonians assigned each of the 7 days to the 7 planets visible to the naked eye, making number 7 important in more than one way. Moreover, the 7-day structure of a week is also believed to have some connections with the Book of Genesis in the Hebrew and Christian Bibles, according to which God created the world in seven days, where six days of work was followed by one day of rest. However, amongst these prevalent notions, the concept of the moon’s phases is the most accepted one.

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Other structures of a week

Although nowadays, the idea of a week with 7 days is prevalent almost everywhere, the number 7 wasn’t the only number associated with the number of days in a week in history. Babylonians went with the 7 days structure. There existed other civilizations for whom the definition of a week was different. For instance, the Egyptians had their own Egyptian calendar where they chose to have a week 10 days long, while for the Romans, their one week lasted for eight days as per their Roman calendar.

However, the Babylonians were such a dominant section of society in terms of culture that slowly, their notion of a week spread throughout the globe. Today, almost every continent, every country, every city, town, and village have got on board with the seven-day week.

Time and again, attempts have been made to change the concept of a seven-day week, but it seems that a 7 day week is here to stay for a prolonged era.

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