Parts of a Second: Essential Knowledge for Scientists

Official SI Definition: The second is 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 cesium-133 atom.

SI System Divisions of the Second

Unit	Symbol	In Seconds (Scientific Notation)	In Seconds (Decimal)
Second	s	10⁰	1 s
Decisecond	ds	10⁻¹	0.1 s
Centisecond	cs	10⁻²	0.01 s
Millisecond	ms	10⁻³	0.001 s
Microsecond	μs	10⁻⁶	0.000001 s
Nanosecond	ns	10⁻⁹	0.000000001 s
Picosecond	ps	10⁻¹²	0.000000000001 s
Femtosecond	fs	10⁻¹⁵	0.000000000000001 s
Attosecond	as	10⁻¹⁸	0.000000000000000001 s
Zeptosecond	zs	10⁻²¹	0.000000000000000000001 s
Yoctosecond	ys	10⁻²⁴	0.000000000000000000000001 s

Scientific Context: Phenomena at Different Timescales

Millisecond (ms)

Human Context: The blink of an eye takes 100-400 ms.

Science & Engineering: The "ping" time for a computer on a local network; the period of a sound wave with a frequency of 1 kHz; camera shutter speeds for fast-action photography.

Microsecond (µs)

Science & Engineering: The time for light to travel about 300 meters (in a vacuum); the switching speed of a modern transistor in a microprocessor; the duration of a short radio-frequency pulse in radar or MRI.

Nanosecond (ns)

Human Context: It takes about 1 ns for light to travel 30 cm (about one foot).

Science & Engineering: The fundamental clock cycle of a 1 GHz computer processor (1 cycle = 1 ns); the time resolution of many particle detectors; the lifetime of an excited molecule before it fluoresces.

Picosecond (ps)

Science & Engineering: The time for a chemical bond vibration; the switching time of the fastest transistors and laser diodes; the temporal resolution of the fastest oscilloscopes and photodetectors.

Femtosecond (fs)

Science & Engineering: The timescale of atomic motion in molecules (1999 Nobel Prize in Chemistry - Ahmed Zewail, "femtochemistry"); the period of visible light (one optical cycle is ~2 fs); the shortest pulses produced by most standard ultrafast lasers.

Attosecond (as)

Science & Engineering: The timescale of electron motion within an atom (2023 Nobel Prize in Physics); the time it takes for an electron to cross a hydrogen atom; the shortest controlled pulses of light ever created.

Zeptosecond (zs) and Yoctosecond (ys)

Science & Engineering: Currently at the frontier of measurement; in 2016, scientists measured the time it took for an electron to be ejected from a helium atom after being hit by a photon: ~850 zeptoseconds; yoctoseconds are mentioned in theoretical physics, such as discussions about the "Planck time".

Units Larger than a Second

Minutes (min): 60 seconds

Hours (h): 3600 seconds

Days (d): 86,400 seconds

Kilosecond (ks): 1,000 seconds (~16.7 minutes) - useful in astronomy

Megasecond (Ms): 1,000,000 seconds (~11.6 days) - used for long-duration experiments or orbital mechanics

Summary for Scientists

A working scientist should be comfortable with the SI prefixes down to at least femtoseconds (10⁻¹⁵ s). The key conceptual breakpoints are:

Milliseconds for physiology and engineering; Microseconds to Nanoseconds for electronics, radar, and computing; Picoseconds to Femtoseconds for chemistry, material science, and atomic physics; Attoseconds and beyond for cutting-edge quantum and atomic physics.

Understanding these scales allows a scientist to choose the right instrumentation and conceptual framework for the system they are studying.