ConstantID

Angstrom star

UnitsMeasured

Å* = 1.000 014 95(90) × 10−10 m

Value
1.000 014 95 × 10−10 m
Standard uncertainty
9 × 10−17 m
Relative uncertainty
9.0 × 10−7 (900 parts per billion)
Status
Measured
Symbol
Å*
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# Angstrom star, CODATA 2022 (NIST)
angstrom_star = 1.00001495e-10  # m, standard uncertainty 9e-17

# SciPy: scipy.constants.physical_constants['Angstrom star']

What it is

A unit of length very close to 10⁻¹⁰ m, defined so that the wavelength of the tungsten Kα₁ X-ray line is exactly 0.209 010 0 Å*. It expressed X-ray wavelengths before they could be tied precisely to the metre.

In other units

UnitValue
CGS (cm)1.000 014 95 × 10−8
nm nanometre0.100 001 495
pm picometre100.001 495
fm femtometre100 001.495
Å ångström1.000 014 95
a₀ bohr (atomic unit)1.889 754 38unit is itself measured

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).

Angstrom star: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−3000−2000−10000+1000+2000+3000parts per billion1998200220062010201420182022

Relative uncertainty

Angstrom star: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻⁸10⁻⁷10⁻⁶1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20221.000 014 95(90) × 10−109.0 × 10−7 +0.0 σ of 2018
20181.000 014 95(90) × 10−109.0 × 10−7 +0.0 σ of 2014
20141.000 014 95(90) × 10−109.0 × 10−7 +0.0 σ of 2010
20101.000 014 95(90) × 10−109.0 × 10−7 −0.0 σ of 2006
20061.000 014 98(90) × 10−109.0 × 10−7 −0.1 σ of 2002
20021.000 015 09(90) × 10−109.0 × 10−7 +0.1 σ of 1998
19981.000 015 01(90) × 10−109.0 × 10−7

“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).