Publications
Partners
In partnership with The Conversation, #Trending brings you Curious Kids, a series in which we ask experts to answer questions from kids.
Why are there seven days in a week? – Henry E, age 8, Somerville, Massachusetts, US
Kristin Heineman, instructor in history, Colorado State University, US:
“Most of our time reckoning is due to the movements of the planets, the moon and the stars. Our day is equal to one full rotation of the earth around its axis. Our year is a rotation of the earth around the sun, which takes 364 and ¼ days, and is why we add an extra day in February every four years, for a leap year.
The moon’s phases do not exactly coincide with the solar calendar. The moon cycle is 27 days and seven hours long, and there are 13 phases of the moon in each solar year.
Some of the earliest civilisations, like the Babylonians, who lived in modern-day Iraq, were astute observers and interpreters of the heavens, and it is largely thanks to them that our weeks are seven days long. The reason they adopted the number seven was that they observed seven celestial bodies – the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. Other civilisations chose other numbers – like the Egyptians, whose week was 10 days long; or the Romans, whose week lasted eight days.
The Babylonians divided their lunar months into seven-day weeks, with the final day of the week holding particular religious significance. The 28-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. However, the Babylonians were such a dominant culture in the Near East, especially in the sixth and seventh centuries BC, that this, and many of their other notions of time – such as a 60-minute hour – persisted.
The seven-day week was then adopted by the Jews, who had been captives of the Babylonians at the height of that civilisation’s power. Other cultures in the surrounding areas also adopted 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.
Finally, once the Romans began to conquer the territory influenced by Alexander the Great, they too shifted to the seven-day week. It was Emperor Constantine who decreed that the seven-day week was the official Roman week and made Sunday a public holiday in AD 321. The weekend was not adopted until modern times in the 20th century.”
To read more of Heineman’s answer, go to theconversation.com
TALK TO US
Hello, curious kids! Have you got a question you’d like an expert to answer?Ask an adult to send it toafrica-curiouskids@theconversation.com. Please tell us your name, age and which city you live in
