Book excerpt: Why are there 7 days in a week and 12 months in a year? What do stars have to do with it? Long ago, people looked up at the night sky. They made up stories to explain the speckled dots of lights. The ancients divided up the year into weeks and days. They assigned “stars” to days and groups of stars to months. We may not know all their stories and beliefs, but we still tell time the same way. Inside this book are the reasons why.