Ancient Egypt refers to a long period of time in history, but there is evidence that Egyptian society once used a lunar calendar before switching to a solar 365-day calendar. They eventually used the stars to predict important agricultural events like the flooding of the Nile River. Their older lunar calendar did not take the Nile flood into account, and it was eventually replaced by one that helped predict the river's flooding.
The Nile flood was one of the most important events in Ancient Egyptian culture. It allowed their society to farm life-sustaining food, and their agricultural livelihood depended on knowing the timing of the flood.
Egyptians eventually realized that they could use stars such as Polaris, or the Dog Star, to predict when the Nile would flood. This stellar calendar became essential for Egyptian agricultural practice, but it did not completely replace the lunar calendar, which was changed and used to determine holidays. Official business, including governmental affairs, relied on the use of the 365-day solar calendar.