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# Physical Constants

The GSL physical constants are defined as Ruby constants under the modules

- `GSL::CONST::MKSA` (MKSA unit)

- `GSL::CONST:CGSM` (CGSM unit)

- `GSL::CONST:NUM` (Dimension-less constants)

For example, the GSL C constant `GSL_CONST_MKSA_SPEED_OF_LIGHT` is represented by a Ruby constant,

    GSL_CONST_MKSA_SPEED_OF_LIGHT  ---> GSL::CONST::MKSA::SPEED_OF_LIGHT

The following lists a part of the constants. Most of the constants are defined both in the modules `GSL::CONST::MKSA` and `GSL::CONST::CGSM`. See also the GSL reference

Contents:

1. Fundamental Constants

2. Astronomy and Astrophysics

3. Atomic and Nuclear Physics

4. Measurement of Time

5. Imperial Units

6. Nautical Units

7. Printers Units

8. Volume

9. Mass and Weight

10. Thermal Energy and Power

11. Pressure

12. Viscosity

13. Light and Illumination

14. Radioactivity

15. Force and Energy

16. Prefixes

17. Examples

## Fundamental Constants

- GSL::CONST::MKSA::SPEED_OF_LIGHT

  The speed of light in vacuum, c.

- GSL::CONST::MKSA::VACUUM_PERMEABILITY

  The permeability of free space, mu (not defined in GSL::CONST::CGSM).

- GSL::CONST::MKSA::VACUUM_PERMITTIVITY

  The permittivity of free space, epsilon_0 (not defined in GSL::CONST::CGSM).

- GSL::CONST::MKSA::PLANCKS_CONSTANT_H

  Planck's constant, `h`.

- GSL::CONST::MKSA::PLANCKS_CONSTANT_HBAR

  Planck's constant divided by 2pi, hbar.

- GSL::CONST::NUM::AVOGADRO

  Avogadro's number

- GSL::CONST::MKSA::FARADAY

  The molar charge of 1 Faraday.

- GSL::CONST::MKSA::BOLTZMANN

  The Boltzmann constant, k.

- GSL::CONST::MKSA::STEFAN_BOLTZMANN_CONSTANT

  The Stefan-Boltzmann constant, sigma.

- GSL::CONST::MKSA::MOLAR_GAS

  The molar gas constant, R_0.

- GSL::CONST::MKSA::STANDARD_GAS_VOLUME

  The standard gas volume, V_0.

- GSL::CONST::MKSA::GAUSS

  The magnetic field of 1 Gauss.

## Astronomy and Astrophysics

- GSL::CONST::MKSA::ASTRONOMICAL_UNIT

  The length of 1 astronomical unit (mean earth-sun distance), AU.

- GSL::CONST::MKSA::GRAVITATIONAL_CONSTANT

  The gravitational constant, G.

- GSL::CONST::MKSA::LIGHT_YEAR

  The distance of 1 light-year, ly.

- GSL::CONST::MKSA::PARSEC

  The distance of 1 parsec, pc.

- GSL::CONST::MKSA::GRAV_ACCEL

  The standard gravitational acceleration on Earth, g.

- GSL::CONST::MKSA::SOLAR_MASS

  The mass of the Sun.

## Atomic and Nuclear Physics

- GSL::CONST::MKSA::ELECTRON_CHARGE

  The charge of the electron, e.

- GSL::CONST::CGSM::ELECTRON_CHARGE_ESU

  The charge of the electron, e, in esu unit (not defined in GSL::CONST::MKSA).

- GSL::CONST::MKSA::ELECTRON_VOLT

  The energy of 1 electron volt, eV.

- GSL::CONST::MKSA::UNIFIED_ATOMIC_MASS

  The unified atomic mass, amu.

- GSL::CONST::MKSA::MASS_ELECTRON

  The mass of the electron, m_e.

- GSL::CONST::MKSA::MASS_MUON

  The mass of the muon, m_mu.

- GSL::CONST::MKSA::MASS_PROTON

  The mass of the proton, m_p.

- GSL::CONST::MKSA::MASS_NEUTRON

  The mass of the proton, m_n.

- GSL::CONST::NUM::FINE_STRUCTURE

  The electromagnetic fine structure constant alpha.

- GSL::CONST::MKSA::RYDBERG

  The Rydberg constant, Ry, in units of energy. This is related to the Rydberg inverse wavelength R by Ry = h c R.

- GSL::CONST::MKSA::THOMSON_CROSS_SECTION

  The Thomson cross section of photon scattering by electrons.

- GSL::CONST::MKSA::BOHR_RADIUS

  The Bohr radius, a_0.

- GSL::CONST::MKSA::ANGSTROM

  The length of 1 angstrom.

- GSL::CONST::MKSA::BARN

  The area of 1 barn.

- GSL::CONST::MKSA::BOHR_MAGNETON

  The Bohr Magneton, mu_B.

- GSL::CONST::MKSA::NUCLEAR_MAGNETON

  The Nuclear Magneton, mu_N.

- GSL::CONST::MKSA::ELECTRON_MAGNETIC_MOMENT

  The absolute value of the magnetic moment of the electron, mu_e. The physical magnetic moment of the electron is negative.

- GSL::CONST::MKSA::PROTON_MAGNETIC_MOMENT

  The magnetic moment of the proton, mu_p.

## Measurement of Time

- GSL::CONST::MKSA::MINUTE

  The number of seconds in 1 minute.

- GSL::CONST::MKSA::HOUR

  The number of seconds in 1 hour.

- GSL::CONST::MKSA::DAY

  The number of seconds in 1 day.

- GSL::CONST::MKSA::WEEK

  The number of seconds in 1 week.

## Imperial Units

- GSL::CONST::MKSA::INCH

  The length of 1 inch.

- GSL::CONST::MKSA::FOOT

  The length of 1 foot.

- GSL::CONST::MKSA::YARD

  The length of 1 yard.

- GSL::CONST::MKSA::MILE

  The length of 1 mile.

- GSL::CONST::MKSA::MIL

  The length of 1 mil (1/1000th of an inch).

## Nautical Units

- GSL::CONST::MKSA::NAUTICAL_MILE

  The length of 1 nautical mile.

- GSL::CONST::MKSA::FATHOM

  The length of 1 fathom.

- GSL::CONST::MKSA::KNOT

  The speed of 1 knot.

## Printers Units

- GSL::CONST::MKSA::POINT

  The length of 1 printer's point (1/72 inch).

- GSL::CONST::MKSA::TEXPOINT

  The length of 1 TeX point (1/72.27 inch).

## Volume

- GSL::CONST::MKSA::ACRE

  The area of 1 acre.

- GSL::CONST::MKSA::LITER

  The volume of 1 liter.

- GSL::CONST::MKSA::US_GALLON

  The volume of 1 US gallon.

- GSL::CONST::MKSA::CANADIAN_GALLON

  The volume of 1 Canadian gallon.

- GSL::CONST::MKSA::UK_GALLON

  The volume of 1 UK gallon.

- GSL::CONST::MKSA::QUART

  The volume of 1 quart.

- GSL::CONST::MKSA::PINT

  The volume of 1 pint.

## Mass and Weight

- GSL::CONST::MKSA::POUND_MASS

  The mass of 1 pound.

- GSL::CONST::MKSA::OUNCE_MASS

  The mass of 1 ounce.

- GSL::CONST::MKSA::TON

  The mass of 1 ton.

- GSL::CONST::MKSA::METRIC_TON

  The mass of 1 metric ton (1000 kg).

- GSL::CONST::MKSA::UK_TON

  The mass of 1 UK ton.

- GSL::CONST::MKSA::TROY_OUNCE

  The mass of 1 troy ounce.

- GSL::CONST::MKSA::CARAT

  The mass of 1 carat.

- GSL::CONST::MKSA::GRAM_FORCE

  The force of 1 gram weight.

- GSL::CONST::MKSA::POUND_FORCE

  The force of 1 pound weight.

- GSL::CONST::MKSA::KILOPOUND_FORCE

  The force of 1 kilopound weight.

- GSL::CONST::MKSA::POUNDAL

  The force of 1 poundal.

## Thermal Energy and Power

- GSL::CONST::MKSA::CALORIE

  The energy of 1 calorie.

- GSL::CONST::MKSA::BTU

  The energy of 1 British Thermal Unit, btu.

- GSL::CONST::MKSA::THERM

  The energy of 1 Therm.

- GSL::CONST::MKSA::HORSEPOWER

  The power of 1 horsepower.

## Pressure

- GSL::CONST::MKSA::BAR

  The pressure of 1 bar.

- GSL::CONST::MKSA::STD_ATMOSPHERE

  The pressure of 1 standard atmosphere.

- GSL::CONST::MKSA::TORR

  The pressure of 1 torr.

- GSL::CONST::MKSA::METER_OF_MERCURY

  The pressure of 1 meter of mercury.

- GSL::CONST::MKSA::INCH_OF_MERCURY

  The pressure of 1 inch of mercury.

- GSL::CONST::MKSA::INCH_OF_WATER

  The pressure of 1 inch of water.

- GSL::CONST::MKSA::PSI

  The pressure of 1 pound per square inch.

## Viscosity

- GSL::CONST::MKSA::POISE

  The dynamic viscosity of 1 poise.

- GSL::CONST::MKSA::STOKES

  The kinematic viscosity of 1 stokes.

## Light and Illumination

- GSL::CONST::MKSA::STILB

  The luminance of 1 stilb.

- GSL::CONST::MKSA::LUMEN

  The luminous flux of 1 lumen.

- GSL::CONST::MKSA::LUX

  The illuminance of 1 lux.

- GSL::CONST::MKSA::PHOT

  The illuminance of 1 phot.

- GSL::CONST::MKSA::FOOTCANDLE

  The illuminance of 1 footcandle.

- GSL::CONST::MKSA::LAMBERT

  The luminance of 1 lambert.

- GSL::CONST::MKSA::FOOTLAMBERT

  The luminance of 1 footlambert.

## Radioactivity

- GSL::CONST::MKSA::CURIE

  The activity of 1 curie.

- GSL::CONST::MKSA::ROENTGEN

  The exposure of 1 roentgen.

- GSL::CONST::MKSA::RAD

  The absorbed dose of 1 rad.

## Force and Energy

- GSL::CONST::MKSA::NEWTON

  The SI unit of force, 1 Newton.

- GSL::CONST::MKSA::DYNE

  he force of 1 Dyne = 10^-5 Newton.

- GSL::CONST::MKSA::JOULE

  The SI unit of energy, 1 Joule.

- GSL::CONST::MKSA::ERG

  The energy 1 erg = 10^-7 Joule.

## Prefixes

- GSL::CONST::NUM::YOTTA

  10^24

- GSL::CONST::NUM::ZETTA

  10^21

- GSL::CONST::NUM::EXA

  10^18

- GSL::CONST::NUM::PETA

  10^15

- GSL::CONST::NUM::TERA

  10^12

- GSL::CONST::NUM::GIGA

  10^9

- GSL::CONST::NUM::MEGA

  10^6

- GSL::CONST::NUM::KILO

  10^3

- GSL::CONST::NUM::MILLI

  10^-3

- GSL::CONST::NUM::MICRO

  10^-6

- GSL::CONST::NUM::NANO

  10^-9

- GSL::CONST::NUM::PICO

  10^-12

- GSL::CONST::NUM::FEMTO

  10^-15

- GSL::CONST::NUM::ATTO

  10^-18

- GSL::CONST::NUM::ZEPTO

  10^-21

- GSL::CONST::NUM::YOCTO

  10^-24

## Example

The following program demonstrates the use of the physical constants in a calculation. In this case, the goal is to calculate the range of light-travel times from Earth to Mars.

    require("gsl")
    include GSL::CONST::MKSA

    puts("In MKSA unit")

    c  = SPEED_OF_LIGHT;
    au = ASTRONOMICAL_UNIT;
    minutes = MINUTE;

    # distance stored in meters
    r_earth = 1.00 * au;
    r_mars  = 1.52 * au;

    t_min = (r_mars - r_earth) / c;
    t_max = (r_mars + r_earth) / c;

    printf("light travel time from Earth to Mars:\n");
    printf("c = %e [m/s]\n", c)
    printf("AU = %e [m]\n", au)
    printf("minutes = %e [s]\n", minutes)
    printf("minimum = %.1f minutes\n", t_min / minutes);
    printf("maximum = %.1f minutes\n\n", t_max / minutes);

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