They found they no longer needed to move from one place to another to survive.

As hunters, people did not need a way to measure time. As farmers, however, they had to plant crops in time to harvest them before winter. They had to know when the seasons would change. So, they developed calendars.

No one knows when the first calendar was developed. But it seems possible that it was based on moons, or lunar months.

When people started farming, the wise men of the tribes became very important. They studied the sky. They gathered enough information so they could know when the seasons would change. They announced when it was time to plant crops.

The divisions of time we use today were developed in ancient Babylonia 4,000 years ago. Babylonian astronomers believed the sun moved around the Earth every 365 days. They divided the trip into 12 equal parts, or months. Each month was 30 days. Then, they divided each day into 24 equal parts, or hours. They divided each hour into 60 minutes, and each minute into 60 seconds.

Humans have used many devices to measure time. The sundial was one of the earliest and simplest.

A sundial measures the movement of the sun across the sky each day. It has a stick or other object that rises above a flat surface. The stick, blocking sunlight, creates a shadow. As the sun moves, so does the shadow of the stick across the flat surface. Marks on the surface show the passing of hours, and perhaps, minutes.