Module constants

source code

List of physical constants (SI, CGS and solar)

Many constants are taken from NIST (http://physics.nist.gov/cuu/Constants/index.html)

Others have their explicit reference listed.

See also ivs.units.conversions for advanced options, such as change the base units are changing the values of the fundamental constants to conventions used by other programs.

Their are two ways one can use the modules in this module:

1. Just use the raw SI values in your script (e.g. constants.Msol. For convenience, also the cgs values of most constants are given, and accessbile via adding the postfix '_cgs', e.g. constants.Msol_cgs.
2. If you always want to use cgs values and thus want the default values to be cgs without bothering with the postfixes, you can change the values of the constants to meet a particular convention via conversions.set_convention. After calling conversions.set_convention('cgs'), the value of constants.Msol will be given in grams instead of kilograms.

The safest way of getting the units of the constants exactly as you want them to be in a script, is via explicitly converting them to the right convention, e.g.

>>> Msol = conversions.convert(constants.Msol_units,'g',constants.Msol)

This is independent of the way the conventions are set.