Marking Time Siriusly

In the history of human civilization, the measurement of time and recording the order and duration of events in the natural world are among the earliest endeavors that might be classified as science…. My [Egyptian] ancestors contributed to the beginning of the science of time…. The Nile Calendar was an essential part of life as it defined the state of yearly flooding with three seasons, the Inundation or Flooding, Planting, and Harvesting—each four months long. A civil year lasting 365 days was ascertained by about 3000 BC or before, based on the average time between arrivals of the flood at Heliopolis, just north of Cairo…. By the time of the First Dynasty of United Egypt under Menes in about 3100 BC, the scientists of the land introduced the concept of the astronomical calendar by observing the event of the heliacal rising of the brilliant star Sothis (or Sirius). Inscribed on the Ivory Tablet, dating from the First Dynasty and now at the University Museum in Philadelphia, were the words, "Sothis, Bringer of the Year and the Inundation."

Ahmed Zewail, Gr’74, Hon’97
1999 Nobel Lecture