Second (s)
The second is the base unit of time in the International System of Units and the foundation for all other time measurements in this converter. It is one of the seven SI base units and the only one that is identical across every system of measurement in the world, from metric to imperial. You encounter seconds constantly: a heartbeat lasts about one second, a traffic light cycle runs for tens of seconds, and computer processors execute billions of operations per second. The second is so fundamental that every other unit in this converter is defined as a multiple or fraction of it.
Definition
One second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. In practical terms, one second equals 1,000 milliseconds, 1/60 of a minute, 1/3,600 of an hour, and 1/86,400 of a day.
History
The division of the day into hours, minutes, and seconds traces back to ancient Babylon, where astronomers used a base-60 number system. The hour was divided into 60 minutes and each minute into 60 seconds, giving the second its name as the second division of the hour by sixty. For most of history the second was defined as 1/86400 of a mean solar day. This definition worked well for everyday purposes but proved inadequate for precision science because the Earth's rotation is not perfectly uniform. In 1967 the thirteenth General Conference on Weights and Measures redefined the second in terms of atomic physics: it is the duration of exactly 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom. This definition, still in force today, makes the second the most precisely defined unit in all of metrology. Atomic clocks based on this definition are accurate to better than one second in 300 million years.
Common Uses
Seconds are the universal currency of precise timekeeping. In sport, race times are recorded to hundredths or thousandths of a second. In music, the tempo of a piece is expressed in beats per minute, each beat a fraction of a second. In computing, processor speeds are measured in gigahertz, meaning billions of clock cycles per second, and network latency is expressed in milliseconds. In cooking, recipes specify boiling times, resting periods, and baking durations in seconds and minutes. In science, the second underpins every measurement of speed, frequency, acceleration, and electrical current.
Did You Know? Facts About Second
- Light travels approximately 299,792 kilometers, or about 186,282 miles, in a single second. In one second, light could circle the Earth more than seven times.
- The human heart beats roughly once per second at rest. Over an average lifetime of 80 years, the heart beats approximately 2.5 billion times.
- The word 'second' comes from the Latin secunda pars minuta, meaning 'second small part', because it is the second division of the hour by sixty. The first division gave us the minute.
- Atomic clocks are so precise that they would only gain or lose one second over roughly 300 million years. GPS satellites rely on this precision to calculate positions to within meters.
- A computer running at 1 GHz executes one billion clock cycles per second. Modern processors run at several GHz, performing trillions of operations every second.