`None` (default), use the ``H0`` attribute from
:mod:`~astropy.cosmology.default_cosmology`.
References
----------
For an illuminating discussion on why you may or may not want to use
little-h at all, see https://arxiv.org/pdf/1308.4150.pdf
"""
if H0 is None:
from .realizations import default_cosmology
H0 = default_cosmology.get().H0
h100_val_unit = u.Unit(100 / (H0.to_value(u.km / u.s / u.Mpc)) * littleh)
return u.Equivalency([(h100_val_unit, None)], "with_H0", kwargs={"H0": H0})
# ===================================================================
# Enable the set of default equivalencies.
# If the cosmology package is imported, this is added to the list astropy-wide.
u.add_enabled_equivalencies(dimensionless_redshift())
# =============================================================================
# DOCSTRING
# This generates a docstring for this module that describes all of the
# standard units defined here.
if __doc__ is not None:
__doc__ += _generate_unit_summary(_ns)
doc="Dex: Base 10 logarithmic unit")
dB = RegularFunctionUnit(['dB', 'decibel'],
0.1 * dex,
namespace=_ns,
doc="Decibel: ten per base 10 logarithmic unit")
mag = RegularFunctionUnit(['mag'],
-0.4 * dex,
namespace=_ns,
doc=("Astronomical magnitude: "
"-2.5 per base 10 logarithmic unit"))
_add_prefixes(mag, namespace=_ns, prefixes=True)
###########################################################################
# CLEANUP
del RegularFunctionUnit
del IrreducibleFunctionUnit
###########################################################################
# DOCSTRING
# This generates a docstring for this module that describes all of the
# standard units defined here.
from astropy.units.utils import generate_unit_summary as _generate_unit_summary
if __doc__ is not None:
__doc__ += _generate_unit_summary(globals())
# These calls are what core.def_unit would do, but we need to use the callable
# unit versions. The actual function unit classes get added in logarithmic.
dex = IrreducibleFunctionUnit(['dex'], namespace=_ns,
doc="Dex: Base 10 logarithmic unit")
dB = RegularFunctionUnit(['dB', 'decibel'], 0.1 * dex, namespace=_ns,
doc="Decibel: ten per base 10 logarithmic unit")
mag = RegularFunctionUnit(['mag'], -0.4 * dex, namespace=_ns,
doc=("Astronomical magnitude: "
"-2.5 per base 10 logarithmic unit"))
_add_prefixes(mag, namespace=_ns, prefixes=True)
###########################################################################
# CLEANUP
del RegularFunctionUnit
del IrreducibleFunctionUnit
###########################################################################
# DOCSTRING
# This generates a docstring for this module that describes all of the
# standard units defined here.
from astropy.units.utils import generate_unit_summary as _generate_unit_summary
if __doc__ is not None:
__doc__ += _generate_unit_summary(globals())