Description
The results of 2408 intensified CCD observations of double stars, made with the 26 inch refractor of the U.S. Naval Observatory, are presented. Each observation of a system represents a combination of over 2000 short-exposure images. These observations are averaged into 1602 mean relative positions and range in separation from 1.94'' to 107.41'', with a median separation of 11.96''. This is the twenty-first in this series of papers and covers the period from 2015 January 13 through 2015 December 19. Significant instrumentation changes are reported in this paper.
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