Another way of evaluating the screw constant is to measure wide, bright pairs whose position angles and separations are well known and relatively fixed. It will be necessary to have up to a dozen of these pairs spread around the sky so that one can be observed at any time of the year. I use this method, and in Table 15.1 I give a list of pairs with relative positions predicted for 2000.0, 2005.0 and 2010.0. As these pairs change only very slowly the positions for future years can be done by simple interpolation.
Was this article helpful?