DO WE NEED TO MODEL PLATES AT ALL

The historical method of obtaining equatorial coordinates for stars ob served via astronomical photography has been to convert the measured c oordinates to equatorial coordinates with the aid of a plate model whi ch corrects for a variety of effects. However, we now have at our disp osal novel smoothing techniques, of considerable generality, which in conjunction with modern star catalogues can reproduce the essence of t he plate model while dramatically minimizing both the fortuitous and s ystematic errors of observation. In this paper we demonstrate that, wi th this technique and extant catalogues, one can obtain, with at least the same precision and better accuracy, the information necessary to transform the measured coordinates successfully into standard coordina tes by a process that involves no sophisticated model for the plate. U sing external checks we estimate the increase in accuracy to be of the order of 25 per cent.