After discussing cosmological distances with an emphasis on practical distance measures for general use in cosmology and extragalactic astronomy, we have obtained a new differential equation, which gives the angular size distance for a class of 'on average' Friedmann-Lemaître cosmological models, that is, models described not only by and but also by , which describes the clumpiness of the distribution of matter. We have also developed a practical numerical method of solving this equation, which we have made publicly available. Since the equation is valid for all cases, this offers for the first time an efficient means of calculating distances in a large class of cosmological models.
The numerical implementation (in FORTRAN77), user's guide and a copy of the latest version of this paper (including appendices) can be obtained from either of the following URLs:
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998