def vradErrorSkyAvg(vmag, spt):
return _vradCalibrationFloor + _vradErrorBCoeff[spt]*exp(_vradErrorACoeff[spt]*(vmag-_vradMagnitudeZeroPoint))<EOL>
Calculate radial velocity error from V and the spectral type. The value of the error is an average over
the sky.

Parameters
----------

vmag - Value of V-band magnitude.
spt  - String representing the spectral type of the star.

Returns
-------

The radial velocity error in km/s.