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Stellarium is a free GPL software which renders realistic skies in real time with OpenGL. It is available for Linux/Unix, Windows and macOS. With Stellarium, you really see what you can see with your eyes, binoculars or a small telescope.
https://stellarium.org
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Crescent visibility: Accuracy & precision of ARCV calculation? #2566

Open hidp123 opened 2 years ago

hidp123 commented 2 years ago

https://github.com/Stellarium/stellarium/blob/e507fc29d57cec5d8d0de84e7c340d747906698c/plugins/Calendars/src/Calendar.cpp#L1214-L1217

The code here for crescent visibility according to Yallop's criterion calculates arc of vision (arcv) as moon altitude - sun altitude. However, looking at Yallop's paper the formula is given as cos ARCV = cos ARCL/cos DAZ. Doing a simple subtraction of altitudes does give a similar answer but I feel there is a loss of precision in doing so.

Regards

github-actions[bot] commented 2 years ago

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gzotti commented 2 years ago

Thanks for your interest. The Calendars plugin is not finished yet, and some of these functions are not even used yet. The code follows that given in a book, not Yallop's paper. There may be better solutions, but they would have to be implemented elsewhere, or as alternative function.

hidp123 commented 2 years ago

Thanks for your response. I am interested and doing some research on the different crescent visibility criteria available. If you don't mind me asking which book are the formulas/code from?

Regards.

Edit: I have found it I believe, Calendrical Calculations - Ultimate Edition, 2018 by Reingold and Dershowitz.

gzotti commented 2 years ago

A comparison of ArcV and related methods, crescent prognosis etc. can be topic of yet another plugin, time permitting.

github-actions[bot] commented 2 years ago

Hello @hidp123! Thank you for this suggestion.