NAME
Astro::Constants - this library provides physical constants for use in Astronomy
VERSION
version 0.12
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 $force_sun_earth = GRAVITATIONAL * MASS_SOLAR * MASS_EARTH / ASTRONOMICAL_UNIT**2;DESCRIPTION
This module provides physical and mathematical constants for use in Astronomy and Astrophysics. The two metric systems of units, MKS and CGS, are kept in two separate modules and are called by name explicitly. It allows you to choose between constants in units of centimetres /grams /seconds with Astro::Constants::CGS and metres /kilograms /seconds with Astro::Constants::MKS.
The :long tag imports all the constants in their long name forms (i.e. GRAVITATIONAL). Useful subsets can be imported with these tags: :fundamental :conversion :mathematics :cosmology :planetary :electromagnetic or :nuclear. Alternate names such as LIGHT_SPEED instead of SPEED_LIGHT or HBAR instead of H_BAR are imported with :alternates. I'd like to move away from their use, but they have been in the module for years. Short forms of the constant names are included to provide backwards compatibility with older versions based on Jeremy Bailin's Astroconst library and are available through the import tag :short.
The values are stored in Physical_Constants.xml in the data directory and are mostly based on the 2014 CODATA values from NIST.
Long name constants are constructed with the constant pragma and are not interpolated in double quotish situations because they are really inlined functions. Short name constants are constructed with the age-old idiom of fiddling with the symbol table using typeglobs, e.g. *PI = \3.14159, and may be slower than the long name constants.
Why use this module
You are tired of typing in all those numbers and having to make sure that they are all correct. How many significant figures is enough or too much? Where's the definitive source, Wikipedia? And which mass does "$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 CGSspeed 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 CGSBoltzmann's constant
This constant is also available using the short name $A_k
GRAVITATIONAL
6.67408e-11 MKS
6.67408e-8 CGSuniversal gravitational constant
This constant is also available using the short name $A_G
ELECTRON_VOLT
1.6021766208e-19 MKS
1.6021766208e-12 CGSelectron volt
This constant is also available using the short name $A_eV
PLANCK
6.626070040e-34 MKS
6.626070040e-27 CGSPlanck constant
This constant is also available using the short name $A_h
H_BAR
1.054571800e-34 MKS
1.054571800e-27 CGSPlanck'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 CGSelectron 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 CGSStefan-Boltzmann constant
This constant is also available using the short name $A_sigma
DENSITY_RADIATION
7.565723e-16 MKS
7.565723e-15 CGSradiation 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 CGSWien wavelength displacement law constant
This constant is also available using the short name $A_Wien
ALPHA
7.2973525664e-3 MKS
7.2973525664e-3 CGSfine structure constant
This constant is also available using the short name $A_alpha
IMPEDANCE_VACUUM
376.730313461characteristic 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 CGSpermittivity 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 CGSpermeability 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
3.14159265358979324trig constant pi
This constant is also available using the short name $A_pi
FOUR_PI
12.5663706143592trig constant pi times 4 (shorthand for some calculations)
This constant is also available using the short name $A_4pi as well as the alternate name FOURPI (imported using the :alternate tag for backwards compatibility)
STERADIAN
57.2957795130823a measure of solid angle in square degrees
This constant is also available using the short name $A_ster
EXP
2.71828182846base of natural logarithm
This constant is also available using the short name $A_exp
ATOMIC_MASS_UNIT
1.660539040e-27 MKS
1.660539040e-24 CGSatomic mass unit, 1 u
This constant is also available using the short name $A_amu
PARSEC
3.08567758149e16 MKS
3.08567758149e18 CGSparsec
This constant is also available using the short name $A_pc
ASTRONOMICAL_UNIT
149_597_870_700 MKS
1.496e13 CGSastronomical unit
This constant is also available using the short name $A_AU
LIGHT_YEAR
9_460_730_472_580_800 MKS
9.4607304725808e17 CGSthe 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 CGSAngstrom
This constant is also available using the short name $A_AA
JANSKY
1e-26 MKS
1e-23 CGSJansky
This constant is also available using the short name $A_Jy
AVOGADRO
6.022140857e23Avogadro's number
This constant is also available using the short name $A_NA
YEAR
31_557_600defined 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_925.1the period of time for the ecliptic longitude of the Sun to increase 360 degrees, approximated by the Gregorian calendar
YEAR_SIDEREAL
31_558_149.8the period of revolution of the Earth around the Sun in a fixed reference frame
YEAR_ANOMALISTIC
31_558_432.6the period between successive passages of the Earth through perihelion
YEAR_ECLIPSE
29_947_974.3the period between successive passages of the Sun (as seen from the geocenter) through the same lunar node
MASS_SOLAR
1.9884e30 MKS
1.9884e33 CGSsolar 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 CGSsolar 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 CGScritical 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
3.0853056e17Hubble 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
2.725cosmic 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
-26.74solar 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
4.83solar 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 CGSsolar 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 CGSmass 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 CGSradius 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
5778surface 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 CGSmean 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 CGSmean 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 CGSsolar 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 CGSEarth 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 CGSlunar 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 CGSlunar 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 CGSlunar 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
0.0549lunar 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 CGSThomson 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 CGSmass 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 CGSmass 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 CGSneutron 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
1.6738e-27mass of Hydrogen atom -- This value is from the IUPAC and is a little smaller than MASS_PROTON + MASS_ELECTRON, but within the uncertainty given here. The current value is 1.008u +/- 0.0002 derived from a range of terrestrial materials. If this is for precision work, you had best understand what you're using. See https://iupac.org/what-we-do/periodic-table-of-elements/
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-27mass of alpha particle
This constant is also available using the short name $A_ma
RADIUS_ELECTRON
2.8179403227e-15 MKS
2.8179403227e-13 CGSclassical 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 CGSBohr 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
Give this method the string of the constant and it returns the precision or uncertainty listed.
$rel_precision = precision('GRAVITATIONAL');
$abs_precision = precision('MASS_EARTH');At the moment you need to know whether the uncertainty is relative or absolute. Looking to fix this in future versions.
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: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
Test::Deep::NumberTolerant for testing values within objects
Reference Documents:
REPOSITORY
* https://github.com/duffee/Astro-Constants
ISSUES
File issues/suggestions at the Github repository https://github.com/duffee/Astro-Constants. The venerable RT is the canonical bug tracker that is clocked by 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 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 - 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) 2017 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.