Talk:Personal equation

"Equation"?
It would be worth clarifying the degree & direction of metaphor involved in the use of "equation" in describing the phenomenon, including whether the term is evoking the math sense (syn'm of "formula") or the act of "equating" that is implicit in recording one's observation as one or several numbers.--Jerzy•t 04:46, 6 December 2016 (UTC)


 * The term "equation" dates from Bessel's time, and it meant an equation in the math sense, representing the difference between two observers. Bessel had a precision instrument to measure the culmination time of stars, i.e. the time when a star crosses the local meridian. In 1821 he invited three other experienced observers (A=Argelander, S=Struve, W=Walbeck) when they were in Königsberg to measure the culmination time of a few specific stars using his instrument, and he compared their results to his own observation (B=Bessel). He wrote the average difference between two observers in the form of an equation:
 * B-A = -1.223 s
 * S-W = -0.242 s, whence B-S = -0.799 s
 * S-A = -0.202 s, whence B-S = -1.021 s
 * The two different results for B-S were not exactly equal, so at that early stage of his investigation Bessel may have refrained from reducing the raw data of pairwise comparisons (the equations) to estimated personal systematic errors. Astronomers have continued to use "personal equation" somewhat loosely to indicate systematic errors in observation that originate in the observer, in contrast to those that arise from instrumental and atmospheric conditions. Ceinturion (talk) 10:53, 18 April 2021 (UTC)