What kind of redshifts are used in NED?
A.: We use heliocentric redshifts. When we display them as velocities, we use the optical convention Vsun = czsun. Note that we do not make any relativistic correction to these velocities. John Huchra at the Harvard-Smithsonian Center for Astrophysics has kindly supplied more information on the definition of extragalactic redshifts. • Q.: Some of the reported redshifts in NED seem to show discrepancies with my estimates. Why? A.: As with the celestial coordinates which we adopt for the objects in NED, we attempt to use the best available redshifts. However, occasional errors creep into NED, in spite of our best efforts. If you find one of these cases, please let us know so that we can fix NED and document the origin of the error. • Q.: Are the redshifts reported in NED spectroscopic or photometric? And what do the codes following the redshift mean? A.: We adopt spectroscopic redshifts whenever they are available. Sometimes, however, only a photometric redshift is available for an objec
