Today, it’s hard not to know the time. Your phone, your TV, your car, and scads of other devices give you the time, accurate to a tiny fraction of a second. But in ages past, telling time wasn’t that easy – especially at night. Fortunately, nature provided a decent nighttime “clock”: the stars. The location of certain stars at different times of year told skywatchers the time of night.

A prime example of how that worked comes from ancient Egypt.

The Egyptian day was divided into 24 hours – a system passed along into modern times. Daytime and nighttime each consisted of 12 hours, regardless of the time of year. So the length of an “hour” varied between night and day, and from season to season.

The nighttime hours were marked by prominent stars. The gap between either the setting times or rising times of two of these stars marked an hour. And each star “reigned” for about 10 days before the next one took its place. So the Egyptian year was divided into 10-day “weeks,” known as decans – 36 in all. An extra five days were added to the end of the year, bringing the calendar to 365 days.

The year began with the first dawn appearance of the star Sirius, the brightest star in all the night sky. It marked the start of the annual flooding of the Nile River, which brought renewed life to the fields – an event marked by the “ticking” of the starry clock.

Script by Damond Benningfield