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Man Pages


Manual Reference Pages  -  ASTRO::CONSTANTS (3)

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NAME

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

CONTENTS

VERSION

version 0.1002

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 <B>Astro::Constants::CGSB> and metres /kilograms /seconds with <B>Astro::Constants::MKSB>.

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 <B>dataB> 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

    SPEED_LIGHT



    2.99792458e8        MKS
    2.99792458e10       CGS



speed of light in a vacuum

This constant is also available using the short name $A_c as well as the alternate name LIGHT_SPEED (imported using the :alternate tag for backwards compatibility)

    BOLTZMANN



    1.38064852e-23      MKS
    1.38064852e-16      CGS



Boltzmann’s constant

This constant is also available using the short name $A_k

    GRAVITATIONAL



    6.67408e-11 MKS
    6.67408e-8  CGS



universal gravitational constant

This constant is also available using the short name $A_G

    ELECTRON_VOLT



    1.6021766208e-19    MKS
    1.6021766208e-12    CGS



electron volt

This constant is also available using the short name $A_eV

    PLANCK



    6.626070040e-34     MKS
    6.626070040e-27     CGS



Planck constant

This constant is also available using the short name $A_h

    H_BAR



    1.054571800e-34     MKS
    1.054571800e-27     CGS



Planck’s constant /2pi

This constant is also available using the short name $A_hbar as well as the alternate name HBAR (imported using the :alternate tag for backwards compatibility)

    ELECTRON_CHARGE



    1.6021766208e-19    MKS
    4.8032046729e-10    CGS



electron charge (defined positive)

This constant is also available using the short name $A_e as well as the alternate name CHARGE_ELEMENTARY (imported using the :alternate tag for backwards compatibility)

    STEFAN_BOLTZMANN



    5.670367e-8 MKS
    5.670367e-5 CGS



Stefan-Boltzmann constant

This constant is also available using the short name $A_sigma

    DENSITY_RADIATION



    7.565723e-16        MKS
    7.565723e-15        CGS



radiation density constant, 4 * sigma / c

This constant is also available using the short name $A_arad as well as the alternate name A_RAD (imported using the :alternate tag for backwards compatibility)

    WIEN



    2.8977729e-3        MKS
    2.8977729e-1        CGS



Wien wavelength displacement law constant

This constant is also available using the short name $A_Wien

    ALPHA



    7.2973525664e-3     MKS
    7.2973525664e-3     CGS



fine structure constant

This constant is also available using the short name $A_alpha

    IMPEDANCE_VACUUM



    376.730313461



characteristic impedance of vacuum

This constant is also available using the short name $A_Z0 as well as the alternate name VACUUM_IMPEDANCE (imported using the :alternate tag for backwards compatibility)

    PERMITIV_FREE_SPACE



    8.854187817e-12     MKS
    1   CGS



permittivity of free space, epsilon_0, the electric constant

This constant is also available using the short name $A_eps0 as well as the alternate name PERMITIVITY_0 (imported using the :alternate tag for backwards compatibility)

    PERMEABL_FREE_SPACE



    1.2566370614e-6     MKS
    1   CGS



permeability of free space, mu_0, the magnetic constant

This constant is also available using the short name $A_mu0 as well as these alternate names (imported using the :alternate tag): PERMEABILITY_0, CONSTANT_MAGNETIC

    PI



    3.14159265358979324



trig constant pi

This constant is also available using the short name $A_pi

    EXP



    2.71828182846



base of natural logarithm

This constant is also available using the short name $A_exp

    ATOMIC_MASS_UNIT



    1.660539040e-27     MKS
    1.660539040e-24     CGS



atomic mass unit, 1 u

This constant is also available using the short name $A_amu

    PARSEC



    3.08567758149e16    MKS
    3.08567758149e18    CGS



parsec

This constant is also available using the short name $A_pc

    ASTRONOMICAL_UNIT



    149_597_870_700     MKS
    1.496e13    CGS



astronomical unit

This constant is also available using the short name $A_AU

    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 is also available using the short name $A_ly

    ANGSTROM



    1e-10       MKS
    1e-8        CGS



Angstrom

This constant is also available using the short name $A_AA

    JANSKY



    1e-26       MKS
    1e-23       CGS



Jansky

This constant is also available using the short name $A_Jy

    AVOGADRO



    6.022140857e23



Avogadro’s number

This constant is also available using the short name $A_NA

    YEAR



    31_557_600



defined as exactly 365.25 days of 86400 SI seconds

This constant is also available using the short name $A_yr as well as the alternate name YEAR_JULIAN (imported using the :alternate tag for backwards compatibility)

    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

    MASS_SOLAR



    1.9884e30   MKS
    1.9884e33   CGS



solar mass

This constant is also available using the short name $A_msun as well as the alternate name SOLAR_MASS (imported using the :alternate tag for backwards compatibility)

    LUMINOSITY_SOLAR



    3.846e26    MKS
    3.846e33    CGS



solar luminosity

This constant is also available using the short name $A_Lsun as well as the alternate name SOLAR_LUMINOSITY (imported using the :alternate tag for backwards compatibility)

    DENSITY_CRITICAL_RHOc



    1.8791e-26  MKS
    1.8791e-29  CGS



critical density /h^2

This constant is also available using the short name $A_rhoc as well as the alternate name RHO_C (imported using the :alternate tag for backwards compatibility)

    HUBBLE_TIME



    3.0853056e17



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

This constant is also available using the short name $A_tH

    TEMPERATURE_CMB



    2.725



cosmic microwave background temperature in Kelvin

This constant is also available using the short name $A_TCMB as well as the alternate name CMB_TEMPERATURE (imported using the :alternate tag for backwards compatibility)

    MAGNITUDE_SOLAR_V



    -26.74



solar V magnitude

This constant is also available using the short name $A_Vsun as well as the alternate name SOLAR_V_MAG (imported using the :alternate tag for backwards compatibility)

    MAGNITUDE_SOLAR_V_ABSOLUTE



    4.83



solar absolute V magnitude

This constant is also available using the short name $A_MVsun as well as the alternate name SOLAR_V_ABS_MAG (imported using the :alternate tag for backwards compatibility)

    RADIUS_SOLAR



    6.96e8      MKS
    6.96e10     CGS



solar radius

This constant is also available using the short name $A_rsun as well as the alternate name SOLAR_RADIUS (imported using the :alternate tag for backwards compatibility)

    MASS_EARTH



    5.9722e24   MKS
    5.9722e27   CGS



mass of Earth

This constant is also available using the short name $A_mearth as well as the alternate name EARTH_MASS (imported using the :alternate tag for backwards compatibility)

    RADIUS_EARTH



    6.378_136_6e6       MKS
    6.378_136_6e8       CGS



radius of Earth

This constant is also available using the short name $A_rearth as well as the alternate name EARTH_RADIUS (imported using the :alternate tag for backwards compatibility)

    TEMPERATURE_SOLAR_SURFACE



    5778



surface temperature of sun

This constant is also available using the short name $A_Tsun as well as the alternate name SOLAR_TEMPERATURE (imported using the :alternate tag for backwards compatibility)

    DENSITY_SOLAR



    1408        MKS
    1.408       CGS



mean solar density

This constant is also available using the short name $A_dsun as well as the alternate name SOLAR_DENSITY (imported using the :alternate tag for backwards compatibility)

    DENSITY_EARTH



    5514        MKS
    5.514       CGS



mean Earth density

This constant is also available using the short name $A_dearth as well as the alternate name EARTH_DENSITY (imported using the :alternate tag for backwards compatibility)

    GRAVITY_SOLAR



    274.0       MKS
    27400       CGS



solar surface gravity

This constant is also available using the short name $A_gsun as well as the alternate name SOLAR_GRAVITY (imported using the :alternate tag for backwards compatibility)

    GRAVITY_EARTH



    9.78        MKS
    978 CGS



Earth surface gravity

This constant is also available using the short name $A_gearth as well as the alternate name EARTH_GRAVITY (imported using the :alternate tag for backwards compatibility)

    RADIUS_LUNAR



    1.7381e6    MKS
    1.7381e8    CGS



lunar radius

This constant is also available using the short name $A_rmoon as well as the alternate name LUNAR_RADIUS (imported using the :alternate tag for backwards compatibility)

    MASS_LUNAR



    7.342e22    MKS
    7.342e25    CGS



lunar mass

This constant is also available using the short name $A_mmoon as well as the alternate name LUNAR_MASS (imported using the :alternate tag for backwards compatibility)

    AXIS_SM_LUNAR



    3.844e8     MKS
    3.844e10    CGS



lunar orbital semi-major axis

This constant is also available using the short name $A_amoon as well as the alternate name LUNAR_SM_AXIS (imported using the :alternate tag for backwards compatibility)

    ECCENTRICITY_LUNAR



    0.0549



lunar orbital eccentricity

This constant is also available using the short name $A_emoon as well as the alternate name LUNAR_ECCENTRICITY (imported using the :alternate tag for backwards compatibility)

    THOMSON_CROSS_SECTION



    6.6524587158e-29    MKS
    6.6524587158e-25    CGS



Thomson cross-section

This constant is also available using the short name $A_sigmaT as well as the alternate name THOMSON_XSECTION (imported using the :alternate tag for backwards compatibility)

    MASS_ELECTRON



    9.10938356e-31      MKS
    9.10938356e-28      CGS



mass of electron

This constant is also available using the short name $A_me as well as the alternate name ELECTRON_MASS (imported using the :alternate tag for backwards compatibility)

    MASS_PROTON



    1.672621898e-27     MKS
    1.672621898e-24     CGS



mass of proton

This constant is also available using the short name $A_mp as well as the alternate name PROTON_MASS (imported using the :alternate tag for backwards compatibility)

    MASS_NEUTRON



    1.674927471e-27     MKS
    1.674927471e-24     CGS



neutron mass

This constant is also available using the short name $A_mn as well as the alternate name NEUTRON_MASS (imported using the :alternate tag for backwards compatibility)

    MASS_HYDROGEN



    1.67372e-24



mass of Hydrogen atom

This constant is also available using the short name $A_mH as well as the alternate name HYDROGEN_MASS (imported using the :alternate tag for backwards compatibility)

    MASS_ALPHA



    6.644_657_230e-27



mass of alpha particle

This constant is also available using the short name $A_ma

    RADIUS_ELECTRON



    2.8179403227e-15    MKS
    2.8179403227e-13    CGS



classical electron radius

This constant is also available using the short name $A_re as well as the alternate name ELECTRON_RADIUS (imported using the :alternate tag for backwards compatibility)

    RADIUS_BOHR



    5.2917721067e-11    MKS
    5.2917721067e-9     CGS



Bohr radius

This constant is also available using the short name $A_a0 as well as the alternate name BOHR_RADIUS (imported using the :alternate tag for backwards compatibility)

    pretty

This is a helper function that rounds a value or list of values to 5 significant figures.

    precision

Currently broken. It will return in v0.11

EXPORT

Nothing is exported by default, so the module doesn’t clobber any of your variables. Select from the following tags:
o :long           (use this one to get the most constants)
o :short
o :fundamental
o :conversion
o :mathematics
o :cosmology
o :planetary
o :electromagnetic
o :nuclear
o :alternates

    Deprecated functions

I’ve gotten rid of list_constants and describe_constants because they are now in the documentation. Use perldoc Astro::Constants for that information.

SEE ALSO

o Astro::Cosmology
o Perl Data Language
o NIST <http://physics.nist.gov>
o Astronomical Almanac <http://asa.usno.navy.mil>
o Neil Bower’s review on providing read-only values <http://neilb.org/reviews/constants.html>
o Test::Number::Delta
o Test::Deep::NumberTolerant for testing values within objects
Reference Documents:
o IAU 2009 system of astronomical constants <http://aa.usno.navy.mil/publications/reports/Luzumetal2011.pdf>
o Astronomical Constants 2016.pdf <http://asa.usno.navy.mil/static/files/2016/Astronomical_Constants_2016.pdf>
o IAU recommendations concerning units <https://www.iau.org/publications/proceedings_rules/units>
o Re-definition of the Astronomical Unit <http://syrte.obspm.fr/IAU_resolutions/Res_IAU2012_B2.pdf>

REPOSITORY

* <https://github.com/duffee/Astro-Constants>

ISSUES

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

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 cpanratings <http://cpanratings.perl.org/rate/?distribution=Astro-Constants>.

    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 - astroconst.org <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@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2016 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.

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