Second (s)
The second is the fundamental SI unit used to measure time. At first, it was defined as 1/86,400 of the average length of a solar day. However, because the Earth’s rotation is not perfectly consistent, this method was imprecise. In 1967, scientists redefined the second based on atomic properties: one second equals the duration of 9,192,631,770 cycles of radiation from a cesium-133 atom. This atomic standard ensures remarkable accuracy in timekeeping, which is essential for technologies like GPS, communications, and scientific experiments. The second remains a cornerstone for tracking and organizing time in today’s world.
Hour (h)
The hour, symbol h, is 60 minutes or 3,600 seconds. It began in ancient times, when people divided the day into 24 parts based on the sun’s movement. This method of dividing the day has remained throughout history. Today, hours organize daily life—jobs, TV, and transport rely on them. The hour is not an SI unit, but it is widely used for convenience and accuracy.