Innovation No. 14 of 77 in the book
The 24-Hour Day
Day and night divided into 12 hours each
- When
- c. 2000 BCE
- Dynasty
- 11th Dynasty
- Era
- Middle Kingdom
Why 24 hours? Because Egypt split day and night into 12 parts each, and the habit stuck. The system is already visible on coffin lids from around 2000 BCE.
By night they told time by 36 star groups, the decans, that rose in sequence; roughly twelve passed between dusk and dawn. By day, shadow clocks marked twelve more.
The hours weren’t even equal — daylight hours stretched in summer and shrank in winter — but the count of twelve-and-twelve never changed.
Every 24-hour day, on every clock and phone, is keeping Egyptian time.
Frequently Asked Questions
What is the earliest archaeological evidence for the 24-hour day in ancient Egypt?
The earliest confirmed evidence dates to approximately 2000 BCE during Egypt's Middle Kingdom (11th Dynasty). Why 24 hours? Because Egypt split day and night into 12 parts each, and the habit stuck. The system is already visible on coffin lids from around 2000 BCE.
How did ancient Egyptians develop the 24-hour day, and what is its legacy?
By night they told time by 36 star groups, the decans, that rose in sequence; roughly twelve passed between dusk and dawn. By day, shadow clocks marked twelve more. Originally, ancient Egyptian hours varied with the seasons: daylight hours were longer in summer and shorter in winter, because daylight was always divided into 12 parts. It was not until Hellenistic astronomers standardized equal hours (equinoctial hours) that modern fixed 60-minute increments emerged.