NAME

Astro::Constants - this library provides physical constants for use in Astronomy

VERSION

version 0.09_92

SYNOPSIS

        use strict;             # important!
    use Astro::Constants::MKS qw/:long/;

        # to calculate the gravitational force of the Sun on the Earth in Newtons, use GMm/r^2
        my $force_sun_earth = GRAVITATIONAL * MASS_SOLAR * MASS_EARTH / ASTRONOMICAL_UNIT**2;

DESCRIPTION

This module provides physical and mathematical constants for use in Astronomy and Astrophysics. The two metric systems of units, MKS and CGS, are kept in two separate modules and are called by name explicitly. It allows you to choose between constants in units of centimetres /grams /seconds with Astro::Constants::CGS and metres /kilograms /seconds with Astro::Constants::MKS.

Short forms of the constant names are included to provide backwards compatibility with older versions based on Jeremy Bailin's Astroconst library and are available through the import tag :short.

The values are stored in Physical_Constants.xml in the data directory and are mostly based on the 2014 CODATA values from NIST.

Long name constants are constructed with the constant pragma and are not interpolated in double quotish situations because they are really inlined functions. Short name constants are constructed with the age-old idiom of fiddling with the symbol table using typeglobs, e.g. *PI = \3.14159, and may be slower than the long name constants. This could do with some benchmarking.

Why use this module

You are tired of typing in all those numbers and having to make sure that they are all correct. How many significant figures is enough or too much? Where's the definitive source, Wikipedia? And which mass does "$m1" refer to, solar or lunar?

The constant values in this module are protected against accidental re-assignment in your code. The test suite protects them against accidental finger trouble in my code. Other people are using this module, so more eyeballs are looking for errors and we all benefit. The constant names are a little longer than you might like, but you gain in the long run from readable, sharable code that is clear in meaning. Your programming errors are a little easier to find when you can see that the units don't match. Isn't it reassuring that you can verify how a number is produced and which meeting of which standards body is responsible for its value?

Trusting someone else's code does carry some risk, which you should consider, but have you also considered the risk of doing it yourself with no one else to check your work?

METHODS

LIGHT_SPEED

    2.99792458e8        MKS
    2.99792458e10       CGS

speed of light in a vacuum

This constant can also be accessed through the variable $A_c (which may be deprecated)

BOLTZMANN

    1.38064852e-23      MKS
    1.38064852e-16      CGS

Boltzmann's constant

This constant can also be accessed through the variable $A_k (which may be deprecated)

GRAVITATIONAL

    6.67408e-11 MKS
    6.67408e-8  CGS

universal gravitational constant

This constant can also be accessed through the variable $A_G (which may be deprecated)

ELECTRON_VOLT

    1.6021766208e-19    MKS
    1.6021766208e-12    CGS

electron volt

This constant can also be accessed through the variable $A_eV (which may be deprecated)

PLANCK

    6.626070040e-34     MKS
    6.626070040e-27     CGS

Planck constant

This constant can also be accessed through the variable $A_h (which may be deprecated)

HBAR

    1.054571800e-34     MKS
    1.054571800e-27     CGS

Planck's constant /2pi

This constant can also be accessed through the variable $A_hbar (which may be deprecated)

ELECTRON_CHARGE

    1.6021766208e-19    MKS
    4.8032046729e-10    CGS

electron charge (defined positive)

This constant can also be accessed through the variable $A_e (which may be deprecated)

STEFAN_BOLTZMANN

    5.670367e-8 MKS
    5.670367e-5 CGS

Stefan-Boltzmann constant

This constant can also be accessed through the variable $A_sigma (which may be deprecated)

A_RAD

    7.565723e-16        MKS
    7.565723e-15        CGS

radiation density constant, 4 * sigma / c

This constant can also be accessed through the variable $A_arad (which may be deprecated)

WIEN

    2.8977729e-3        MKS
    2.8977729e-1        CGS

Wien wavelength displacement law constant

This constant can also be accessed through the variable $A_Wien (which may be deprecated)

ALPHA

    7.2973525664e-3     MKS
    7.2973525664e-3     CGS

fine structure constant

This constant can also be accessed through the variable $A_alpha (which may be deprecated)

VACUUM_IMPEDANCE

    376.730313461

characteristic impedance of vacuum

This constant can also be accessed through the variable $A_Z0 (which may be deprecated)

PERMITIV_FREE_SPACE

    8.854187817e-12     MKS
    1   CGS

permittivity of free space, epsilon_0, the electric constant

This constant can also be accessed through the variable $A_eps0 (which may be deprecated)

PERMEABL_FREE_SPACE

    1.2566370614e-6     MKS
    1   CGS

permeability of free space, mu_0, the magnetic constant

This constant can also be accessed through the variable $A_mu0 (which may be deprecated)

PI

    3.14159265358979324

trig constant pi

This constant can also be accessed through the variable $A_pi (which may be deprecated)

EXP

    2.71828182846

base of natural logarithm

This constant can also be accessed through the variable $A_exp (which may be deprecated)

ATOMIC_MASS_UNIT

    1.660539040e-27     MKS
    1.660539040e-24     CGS

atomic mass unit, 1 u

This constant can also be accessed through the variable $A_amu (which may be deprecated)

PARSEC

    3.08567758149e16    MKS
    3.08567758149e18    CGS

parsec

This constant can also be accessed through the variable $A_pc (which may be deprecated)

ASTRONOMICAL_UNIT

    149_597_870_700     MKS
    1.496e13    CGS

astronomical unit

This constant can also be accessed through the variable $A_AU (which may be deprecated)

LIGHT_YEAR

    9_460_730_472_580_800       MKS
    9.4607304725808e17  CGS

the distance that light travels in vacuum in one Julian year

This constant can also be accessed through the variable $A_ly (which may be deprecated)

ANGSTROM

    1e-10       MKS
    1e-8        CGS

Angstrom

This constant can also be accessed through the variable $A_AA (which may be deprecated)

JANSKY

    1e-26       MKS
    1e-23       CGS

Jansky

This constant can also be accessed through the variable $A_Jy (which may be deprecated)

AVOGADRO

    6.022140857e23

Avogadro's number

This constant can also be accessed through the variable $A_NA (which may be deprecated)

YEAR

    31_557_600

defined as exactly 365.25 days of 86400 SI seconds

This constant can also be accessed through the variable $A_yr (which may be deprecated)

YEAR_TROPICAL

    31_556_925.1

the period of time for the ecliptic longitude of the Sun to increase 360 degrees, approximated by the Gregorian calendar

YEAR_SIDEREAL

    31_558_149.8

the period of revolution of the Earth around the Sun in a fixed reference frame

YEAR_ANOMALISTIC

    31_558_432.6

the period between successive passages of the Earth through perihelion

YEAR_ECLIPSE

    29_947_974.3

the period between successive passages of the Sun (as seen from the geocenter) through the same lunar node

SOLAR_MASS

    1.9884e30   MKS
    1.9884e33   CGS

solar mass

This constant can also be accessed through the variable $A_msun (which may be deprecated)

SOLAR_LUMINOSITY

    3.846e26    MKS
    3.846e33    CGS

solar luminosity

This constant can also be accessed through the variable $A_Lsun (which may be deprecated)

RHO_C

    1.8791e-26  MKS
    1.8791e-29  CGS

critical density /h^2

This constant can also be accessed through the variable $A_rhoc (which may be deprecated)

HUBBLE_TIME

    3.0853056e17

Hubble time *h, the inverse of Hubble's constant valued at 100 km/s/Mpc (DEPRECATED - see ChangeLog)

This constant can also be accessed through the variable $A_tH (which may be deprecated)

CMB_TEMPERATURE

    2.725

cosmic microwave background temperature

This constant can also be accessed through the variable $A_TCMB (which may be deprecated)

SOLAR_V_MAG

    -26.74

solar V magnitude

This constant can also be accessed through the variable $A_Vsun (which may be deprecated)

SOLAR_V_ABS_MAG

    4.83

solar absolute V magnitude

This constant can also be accessed through the variable $A_MVsun (which may be deprecated)

SOLAR_RADIUS

    6.96e8      MKS
    6.96e10     CGS

solar radius

This constant can also be accessed through the variable $A_rsun (which may be deprecated)

EARTH_MASS

    5.9722e24   MKS
    5.9722e27   CGS

mass of Earth

This constant can also be accessed through the variable $A_mearth (which may be deprecated)

EARTH_RADIUS

    6.378_136_6e6       MKS
    6.378_136_6e8       CGS

radius of Earth

This constant can also be accessed through the variable $A_rearth (which may be deprecated)

SOLAR_TEMPERATURE

    5778

surface temperature of sun

This constant can also be accessed through the variable $A_Tsun (which may be deprecated)

SOLAR_DENSITY

    1408        MKS
    1.408       CGS

mean solar density

This constant can also be accessed through the variable $A_dsun (which may be deprecated)

EARTH_DENSITY

    5514        MKS
    5.514       CGS

mean Earth density

This constant can also be accessed through the variable $A_dearth (which may be deprecated)

SOLAR_GRAVITY

    274.0       MKS
    27400       CGS

solar surface gravity

This constant can also be accessed through the variable $A_gsun (which may be deprecated)

EARTH_GRAVITY

    9.78        MKS
    978 CGS

Earth surface gravity

This constant can also be accessed through the variable $A_gearth (which may be deprecated)

LUNAR_RADIUS

    1.7381e6    MKS
    1.7381e8    CGS

lunar radius

This constant can also be accessed through the variable $A_rmoon (which may be deprecated)

LUNAR_MASS

    7.342e22    MKS
    7.342e25    CGS

lunar mass

This constant can also be accessed through the variable $A_mmoon (which may be deprecated)

LUNAR_SM_AXIS

    3.844e8     MKS
    3.844e10    CGS

lunar orbital semi-major axis

This constant can also be accessed through the variable $A_amoon (which may be deprecated)

LUNAR_ECCENTRICITY

    0.0549

lunar orbital eccentricity

This constant can also be accessed through the variable $A_emoon (which may be deprecated)

THOMSON_XSECTION

    6.6524587158e-29    MKS
    6.6524587158e-25    CGS

Thomson cross-section

This constant can also be accessed through the variable $A_sigmaT (which may be deprecated)

ELECTRON_MASS

    9.10938356e-31      MKS
    9.10938356e-28      CGS

mass of electron

This constant can also be accessed through the variable $A_me (which may be deprecated)

PROTON_MASS

    1.672621898e-27     MKS
    1.672621898e-24     CGS

mass of proton

This constant can also be accessed through the variable $A_mp (which may be deprecated)

NEUTRON_MASS

    1.674927471e-27     MKS
    1.674927471e-24     CGS

neutron mass

This constant can also be accessed through the variable $A_mn (which may be deprecated)

HYDROGEN_MASS

    1.67372e-24

mass of Hydrogen atom

This constant can also be accessed through the variable $A_mH (which may be deprecated)

MASS_ALPHA

    6.644_657_230e-27

mass of alpha particle

This constant can also be accessed through the variable $A_ma (which may be deprecated)

ELECTRON_RADIUS

    2.8179403227e-15    MKS
    2.8179403227e-13    CGS

classical electron radius

This constant can also be accessed through the variable $A_re (which may be deprecated)

BOHR_RADIUS

    5.2917721067e-11    MKS
    5.2917721067e-9     CGS

Bohr radius

This constant can also be accessed through the variable $A_a0 (which may be deprecated)

EXPORT

Nothing is exported by default, so the module doesn't clobber any of your variables. Select from the following tags:

• long (use this one to get the most constants)

• short

• fundamental

• conversion

• mathematics

• cosmology

• planetary

• electromagnetic

• nuclear

SEE ALSO

• Astro::Cosmology

• PDL

• http://physics.nist.gov/|NIST

• http://asa.usno.navy.mil

• http://neilb.org/reviews/constants.html

• Test::Number::Delta

• Test::Deep::NumberTolerant for testing values within objects

Reference Documents: =for :list * http://aa.usno.navy.mil/publications/reports/Luzumetal2011.pdf * http://asa.usno.navy.mil/static/files/2016/Astronomical_Constants_2016.pdf * https://www.iau.org/publications/proceedings_rules/units/ * http://syrte.obspm.fr/IAU_resolutions/Res_IAU2012_B2.pdf

ISSUES

File issues/suggestions at the Github repository https://github.com/duffee/Astro-Constants/. The venerable https://rt.cpan.org/Dist/Display.html?Status=Active&Queue=Astro-Constants|RT is the canonical bug tracker that is clocked by https://metacpan.org/pod/Astro::Constants|meta::cpan.

Using strict is a must with this code. Any constants you forgot to import will evaluate to 0 and silently introduce errors in your code. Caveat Programmer.

If you are using this module, drop me a line using any available means at your disposal, including *gasp* email (address in the Author section), to let me know how you're using it. What new features would you like to see? If you've had an experience with using the module, let other people know what you think, good or bad, by rating it at http://cpanratings.perl.org/rate/?distribution=Astro-Constants|cpanratings.

Extending the data set

If you want to add in your own constants or override the factory defaults, run make, edit the PhysicalConstants.xml file and then run dzil build again. If you have a pre-existing PhysicalConstants.xml file, drop it in place before running dzil build.

Availability

the original astroconst sites have disappeared

ROADMAP

I plan to deprecate the short names and change the order in which long names are constructed, moving to a noun_adjective format. LIGHT_SPEED and SOLAR_MASS become SPEED_LIGHT and MASS_SOLAR. This principle should make the code easier to read with the most important information coming at the beginning of the name.

ASTROCONST

(Gleaned from the Astroconst home page - http://web.astroconst.org )

Astroconst is a set of header files in various languages (currently C, Fortran, Perl, Java, IDL and Gnuplot) that provide a variety of useful astrophysical constants without constantly needing to look them up.

The generation of the header files from one data file is automated, so you can add new constants to the data file and generate new header files in all the appropriate languages without needing to fiddle with each header file individually.

This package was created and is maintained by Jeremy Bailin. It's license states that it is completely free, both as in speech and as in beer.

DISCLAIMER

No warranty expressed or implied. This is free software. If you want someone to assume the risk of an incorrect value, you better be paying them.

(What would you want me to test in order for you to depend on this module?)

from Jeremy Bailin's astroconst header files

The Astroconst values have been gleaned from a variety of sources, and have quite different precisions depending both on the known precision of the value in question, and in some cases on the precision of the source I found it from. These values are not guaranteed to be correct. Astroconst is not certified for any use whatsoever. If your rocket crashes because the precision of the lunar orbital eccentricity isn't high enough, that's too bad.

ACKNOWLEDGMENTS

Jeremy Balin, for writing the astroconst package and helping test and develop this module.

Doug Burke, for giving me the idea to write this module in the first place, tidying up Makefile.PL, testing and improving the documentation.

AUTHOR

Boyd Duffee <duffee at cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by Boyd Duffee.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

cpanm Astro::Constants

perl -MCPAN -e shell
install Astro::Constants