The first step in reducing the position angle - either the observed or calculated position angle - is to apply the correction for proper motion. The change in position angle due to proper motion is given by
where A6^ is the change in position angle due to proper motion, p.a is the proper motion in right ascension in seconds of time per year,
¿is the declination of the star, t is the epoch of observation, and t0 is the epoch to which the position angle is being referred.
The constant converts seconds of time (of the proper motion in right ascension) to degrees.
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