Atomic unit of time
UnitsMeasured
= 2.418 884 326 5864(26) × 10−17 s
- Value
- 2.418 884 326 5864 × 10−17 s
- Standard uncertainty
- 2.6 × 10−29 s
- Relative uncertainty
- 1.1 × 10−12 (1.1 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# atomic unit of time, CODATA 2022 (NIST)
atomic_unit_of_time = 2.4188843265864e-17 # s, standard uncertainty 2.6e-29
# SciPy: scipy.constants.physical_constants['atomic unit of time']What it is
The unit of time in the Hartree system of atomic units, where the electron mass, the elementary charge, ħ and 4πε₀ are all set to 1. Its value here is the SI equivalent of one atomic unit.
In other units
| Unit | Value | |
|---|---|---|
| fs femtosecond | 0.024 188 843 2659 |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 2.418 884 326 5864(26) × 10−17 | 1.1 × 10−12 | +0.1 σ of 2018 |
| 2018 | 2.418 884 326 5857(47) × 10−17 | 1.9 × 10−12 | +5.5 σ of 2014 |
| 2014 | 2.418 884 326 509(14) × 10−17 | 5.8 × 10−12 | +0.6 σ of 2010 |
| 2010 | 2.418 884 326 502(12) × 10−17 | 5.0 × 10−12 | −0.2 σ of 2006 |
| 2006 | 2.418 884 326 505(16) × 10−17 | 6.6 × 10−12 | +0.0 σ of 2002 |
| 2002 | 2.418 884 326 505(16) × 10−17 | 6.6 × 10−12 | +0.3 σ of 1998 |
| 1998 | 2.418 884 326 500(18) × 10−17 | 7.4 × 10−12 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).