## Example

The position angle for alpha Centauri for the year 2000 is 222°3. Calculate the change in the position angle over the fifty-year period 2000 to 2050. We have a = 14h 39m 35.885s (= 219°89952) 8 = -60° 50' 07'.'44 (= -60°8354) Ha = -0.49826 s (= -0°00207608) 6 = 222°3 t0 = 2000 t = 2050.

Carrying out the calculations gives A6 = -0°.3 and hence 60 = 222°0. So there is a change of -0°.3 over the 50-year period due simply to procession and proper motion. (Note: 222°0 is not the position angle for the year 2050, but the position angle for the year 2000 referred to the pole of the year 2050.)

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