Apparent vs. "True" Achronycal and Cosmical Rising/Setting

Asked by Anthony Kaye on 2017-07-03

Although I think the calculations for the heliacal rising/setting seem to be correct, the acronycal rise/set and cosmical rise/set dates seem to be almost six months different when compared to other calculations of the same object at the same location, same elevation, and same year.

Is it possible that Stellarium is computing a "true" acronycal rise/set and a "true" cosmical rise/set instead of apparent dates? If so, what is the necessary correction?

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gzotti (georg-zotti) said :

Cosmic and acronychic rise and set are purely geometric, unobservable. Cosmic rise (rising together with the sun) is usually somewhat before Heliacal rise, etc. I am not aware of "apparent" models for cosmic/acronychal. Paper hints welcome, together with working code even more.

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gzotti (georg-zotti) said :

It seems this is the same discussion that continued much further on SF:

Net result: The terminology is sometimes reversed in the literature. So our acronychal setting may be other authors' cosmical setting etc, but Stellarium's plugin description declares our reading of the terminology.

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