The Beatles wrote 8 days a week, which begs the question why does a week have 7 days. A day is defined by rotation, as is a year. The months are roughly in line with the lunar orbit. 24 hours, 60 minutes and 60 seconds are all logical mathematically. But 7 days a week. Why is it a prime number? 7 does not fit into a month apart from 3 of 4 years for February.