astropy.units.doppler_radio(rest)[source]

Return the equivalency pairs for the radio convention for velocity.

The radio convention for the relation between velocity and frequency is:

$$V = c \frac{f_0 - f}{f_0} ; f(V) = f_0 ( 1 - V/c )$$

Parameters
restQuantity

Any quantity supported by the standard spectral equivalencies (wavelength, energy, frequency, wave number).

References

NRAO site defining the conventions

Examples

>>> import astropy.units as u
>>> CO_restfreq = 115.27120*u.GHz  # rest frequency of 12 CO 1-0 in GHz