crow

Utility library

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Constants

#include "crow/constants.hpp"
namespace Crow;

All of the constants defined here follow the conventions of the standard <numbers> header. Each constant is defined in two forms:

constexpr double name = [value as double];
template <std::floating_point T> constexpr T name_v = [value as T];

For the physical and astronomical constants, long and short versions of the constant names are provided. The short symbol-named constants (but not the full-named equivalents) are in the Constants sub-namespace to avoid name collisions.

The values quoted here are approximate; the values actually supplied are accurate to the precision of the type or to the best known precision, whichever is appropriate.

Constants

Conversion factors

Constant	Value
`arcsec`	4.84814×10^-6 rad
`arcmin`	2.90888×10^-4 rad
`degree`	0.0174533 rad
`inch`	0.0254 m
`foot`	0.3048 m
`yard`	0.9144 m
`mile`	1609.344 m
`nautical_mile`	1852 m
`ounce`	0.0283495 kg
`pound`	0.453592 kg
`short_ton`	907.185 kg
`long_ton`	1016.05 kg
`pound_force`	4.44822 N
`erg`	10^-7 J
`foot_pound`	1.35582 J
`calorie`	4.184 J
`kilocalorie`	4184 J
`ton_tnt`	4.184×10⁹ J
`horsepower`	745.700 W
`mmHg`	133.322 Pa
`atmosphere`	101325 Pa
`zero_celsius`	273.15 K

Physical constants

Sources:

CODATA recommended values

Values related to quantity of substance are given in kilomoles to avoid intrusive factors of 1000 in expressions.

Constant	Symbol	Value
`alpha_particle_mass`	`m_alpha`	6.64466×10^-27 kg
`atomic_mass_constant`	`m_u`	1.66054×10^-27 kg
`avogadro_constant`	`N_A`	6.02214×10²⁶ kmol^-1
`boltzmann_constant`	`k`	1.38065×10^-23 J/K
`electron_mass`	`m_e`	9.10938×10^-31 kg
`elementary_charge`	`ec`	1.60218×10^-19 C
`fine_structure_constant`	`alpha`	7.29735×10^-3 dimensionless
`first_radiation_constant`	`c_1`	3.74177×10^-16 W m²
`gravitational_constant`	`G`	6.67428×10^-11 m³ kg^-1 s^-2
`josephson_constant`	`K_J`	4.83598×10¹⁴ Hz V^-1
`molar_gas_constant`	`R`	8314.46 J kmol^-1 K^-1
`neutron_mass`	`m_n`	1.67493×10^-27 kg
`planck_constant`	`h`	6.62607×10^-34 J s
`proton_mass`	`m_p`	1.67262×10^-27 kg
`rydberg_constant`	`R_inf`	1.09737×10⁷ m^-1
`second_radiation_constant`	`c_2`	0.0143878×10^-2 m K
`speed_of_light`	`c`	2.99792×10⁸ m/s
`stefan_boltzmann_constant`	`sigma`	5.67037×10^-8 W m^-2 K^-4
`vacuum_impedance`	`Z_0`	376.730 Ω
`vacuum_permeability`	`mu_0`	1.25664×10^-6 N A^-2
`vacuum_permittivity`	`epsilon_0`	8.85419×10^-12 F m^-1
`von_klitzing_constant`	`R_K`	25812.8 Ω
`wien_constant`	`b_W`	2.89777×10^-3 m K

Astronomical constants