Why do weeks have 7 days

So, that number held particular significance to them. Other civilizations chose other numbers — like the Egyptians, whose week was 10 days long; or the Romans, whose week lasted eight. The Babylonians divided their lunar months into seven-day weeks, with the final day of the week holding particular religious significance.

The day month, or a complete cycle of the Moon, is a bit too large a period of time to manage effectively, and so the Babylonians divided their months into four equal parts of seven. The number seven is not especially well-suited to coincide with the solar year, or even the months, so it did create a few inconsistencies.

However, the Babylonians were such a dominant culture in the Near East, especially in the sixth and seventh centuries B. The seven-day week spread throughout the Near East. Other cultures in the surrounding areas got on board with the seven-day week, including the Persian empire and the Greeks. Centuries later, when Alexander the Great began to spread Greek culture throughout the Near East as far as India, the concept of the seven-day week spread as well.

Enter the Babylonians. This ancient society, who lived in Mesopotamia in what is now Iraq , rounded the Moon cycle down to 28 days and divided this time span into 4 periods of 7 days each, using leap days to stay in sync with the Moon phases in the long run.

This 7-day structure is also believed to have ultimately informed a number of popular creation myths, such as the Book of Genesis in the Hebrew and Christian Bibles, which states that God created the world in seven days: six days of work followed by one day of rest. Avid astronomers and astrologers, the Babylonians developed a kind of horoscope around BCE where each day of the week was assigned to one of the classical planets — the seven non-fixed celestial bodies visible to the naked eye.

Some historical sources claim that the connection between the days of the week and the classical planets was introduced later by the ancient Greeks. However, historians generally agree that it was the Romans who, a few hundred years later, added many features of the modern 7-day week by adapting the Babylonian system to their world view.

From around the 1st century BCE, they introduced a system where each day was named after one of their pagan gods, each of whom was associated with one of the classical planets. Buy Now. How old is Earth? How fast can you think? How long is a light year and how short is a femtosecond? What does Greenwich Mean Time mean? Can you tell the time with flowers? When did time begin?

After all, a typical year has days. Why don't we have 73 five-day weeks? Or 26 day weeks? When you think about it, couldn't we divvy up those days anyway we like? Why have we always had seven-day weeks then? The easy answer is because it's been that way for a really long time. The seven-day week dates back thousands of years. Historians believe it probably got its start with the ancient Babylonians. Our other time periods can be traced to natural sources, such as the movement of the Earth, Moon , and Sun.

For example, Earth's rotation on its axis gives us our day. The movement of Earth around the Sun gives us our year. The Moon's phases even approximate our months. However, there is no natural explanation for the seven-day week. Some experts believe the ancient Babylonians may have adopted a seven-day week to approximate the individual cycles of the Moon throughout the month.

These cycles, however, only imperfectly line up with a seven-day week, requiring an extra day or two to be added to one week every few months.

Why did the ancient Babylonians settle on a seven-day week then? Some experts believe it's because the ancient Babylonians believed the number seven had a mystical significance to it. This belief may have stemmed from their focus on the seven heavenly bodies they knew of at that time: the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. The tendency to perform rituals every seven days may have given rise to the seven-day week. Experts also believe these same celestial bodies may have led other ancient cultures, including the Chinese and Japanese, to adopt their own seven-day weeks.

The development of the seven-day week in other cultures can be traced to the creation story in the Bible. According to the Book of Genesis, God created everything in the world in six days and then rested the seventh day.

Many believe this provided a model for early cultures to follow: work six days and rest on the seventh day. Our modern calendars still adhere to the seven-day week. Scholars believe its formal adoption by Roman Emperor Constantine in solidified its acceptance worldwide. Constantine established Sunday, the Christian Sabbath, as the first day of the week and Saturday, the Jewish Sabbath, as the last day of the week.

Many calendars and cultures around the world still observe Sunday as the first day of the week. Practically, however, with the modern five-day work week and two-day weekend, many people informally consider Monday to be the first day of the week and Sunday the last.

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