21 July

1620: On 21 July 1620, Jean Picard was born.

Picard is regarded as the founder of modern astronomy in France. He introduced new methods, improved the old instruments and added new devices, such as Huygens's pendulum clock to record times and time intervals.

Picard was also the first to put the telescope to use for the accurate measurement of small angles.

His most important work was the first measurement of the circumference of Earth.