Celestial Coordinates Paper II applies the general formalism of Paper I to the problem of representing celestial coordinate systems. The projections support terrestrial and planetary mapping as well as celestial mapping. This is fixed for each class of projection. Oblique projections are generated naturally in this fashion as illustrated in Figure 2 . Spectral coordinates Paper III extends the methods of Papers I and II to represent frequency, wavelength, and velocity including the radio, optical and redshift conventional velocities.
Provision is made for higher order pixel corrections.
Keywords are defined to specify velocity coordinate reference frames and any parameters needed to switch between them. Methods to describe the dependence of spectral coordinates on celestial coordinates are given for velocity reference frames and for instruments similar to Fabry-Perot interferometers. When these data are reduced to tabular form, they are easily described by the conventions presented in all three papers for such data. AIPS Memo No. 27, National Radio Astronomy Observatory, Charlottesville, Virginia IAU Style Manual 1983, IAU Inf.