Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] are there seven days in a week? – Henry E., age 8, Somerville, MassachusettsWaiting for the weekend can often seem unbearable, a whole six days between Saturdays. Having seven days in a week has been the case for a very long time, and so people don’t often stop to ask why.Most of our time reckoning is due to the movements of the planets, Moon and stars. Our day is equal to one full rotation of the Earth around its axis. Our year is a revolution of the Earth around the Sun, which takes 365 and ¼ days, which is why we add an extra day in February every four years, for a leap year.AdvertisementAdvertisementBut the week and the month are a bit trickier. The phases of the Moon 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 civilizations observed the cosmos and recorded the movements of planets, the Sun and Moon. 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. 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 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.AdvertisementAdvertisementThe number seven is not especially well-suited to coincide with the solar year, or even the months, so it did create a few inconsisten …
