caput.astro.constants#

Constants and conversions for astronomy and cosmology.

Re-exports all constants in scipy.constants, along with a few extras.

Dynamic prefixes are also supported, using all prefixes defined in scipy.constants. Prefixes are separated from the unit by an underscore.

Examples#

Prefixes are automatically multiplied. In this example, the kilo prefix multiplies the base unit gram.

>>> from caput.astro import constants
>>> constants.kilo_gram
1.0

`UT1_second`	The approximate length of a UT1 second in SI seconds (i.e. LOD / 86400). This was
`a_rad`	Radiation constant (in J m^-3 K^-4}, equal to 4 * Stefan_Boltzmann / c.
`nu21`	21cm transition frequency (in MHz).
`second`	One second in seconds.
`sidereal_second`	Approximate number of seconds in a sidereal second.
`solar_mass`	Solar mass in kg.
`stellar_second`	Approximate length of a stellar second.
`t_sidereal`	One sidereal day in SI seconds. This is sidereal_second * day.

UT1_second: float = 1.00000000205#: The approximate length of a UT1 second in SI seconds (i.e. LOD / 86400). This was calculated from the IERS EOP C01 IAU2000 data, by calculating the derivative of UT1 - TAI from 2019.5 to 2020.5. Note that the variations in this are quite substantial, but it’s typically 1ms over the course of a day.

a_rad: float#: Radiation constant (in J m^-3 K^-4}, equal to 4 * Stefan_Boltzmann / c.

sidereal_second: float = 0.9972695683734868#: Approximate number of seconds in a sidereal second. The exact value used here is from https://hpiers.obspm.fr/eop-pc/models/constants.html but can be derived from USNO Circular 179 Equation 2.12.

stellar_second: float = 0.9972696652815595#: Approximate length of a stellar second. This comes from the definition of ERA-UT1 (see IERS Conventions TR Chapter 1) giving the first ratio a UT1 and stellar second.

t_sidereal: float = 86164.09070746927#: One sidereal day in SI seconds. This is sidereal_second * day.