"Cool Met Stuff": Why “one second” is one second?

12 September 2025

From ancient times, when people observed celestial phenomena to determine day and night, to modern times, when time is determined by the frequency of atomic oscillations, timekeeping methods have undergone significant changes. This new episode of "Cool Met Stuff" will explore the origins of time units and the definition of "one second", and explain how modern technology ensures the accuracy and stability of time services.

The video is now available on the "MyObservatory" mobile application and the Observatory's website for your viewing (programme is broadcasted in Cantonese).

Welcome to view "Cool Met Stuff" from this link (broadcast in Cantonese).
Broadcast schedule of various TV channels can be found here.