Julian Day

[Skaperen]

it accepted 1752, 9, 5 when i tried it and it gave a Julian day.  that date did not happen in the British empire (see https://en.wikipedia.org/wiki/1752). try "cal 1752" in a Linux shell and look at September. has this been tested with the BC leap years (e.g. 15 BC, 2, 29 should be valid)?  does it do leap years before 46 BC?  does it handle the varied start of a new year through history? calendar history is complex.  if the tool is applicable to history it too, would be complex.

how would the print calls work in a GUI environment?  will they pop up error windows?

Lets remember, the Julian Day is a count of the number of days, in the case of this formula it is from -4712 thru 2100. The fact that a specific date did not exist, as in the example given, or those in the conversion from the Julian Calendar to the Gregorian Calendar, etc. does not mean that a day did not exist.

"e.g. 15 BC, 2, 29 should be valid?", In the astronomical version of Julian day, yes it is valid and has a Julian Day of 1715638.5, in the historical version of Julian day it is not, in fact it is the equivalent of 16 BC Mar 1. (remembering that the astronomical has a year "0", historical does not)

"if the tool is applicable to history it too, would be complex."  Fortunately it is not concerned with history, only a sequence of days :-)

"how would the print calls work in a GUI environment?  will they pop up error windows?"  I don't know, I will defer that to someone experienced in GUI's

what we are basically dealing with is a mapping between a logical system to identify real days (earth rotation) in a linear numeric way (the JD) with a social construct (a calendar system with months and days).  if igot to redesign it, months would be gone and leap years would the common every 4 years as in Gregorin with an exception every 128 years. dates would be seasons and a number, 0 .. 91, accounting for the split days at season boundaries (91.310625 days in a season) ... for example "Winter 35".  the leap day would be inserted (not having a part of any season instead of being added to one) when the accumulated error reaches 12.xxx hours (which then become -11.xxx hours). it's just another social system the has not been adopted (the Gregorian calendar is the official one, not the Skaperenan calendar).

the calendar of choice defines the mapping of history (of choice).  the JD that maps to 2 Sept 1752 should be 1.0 less than the day after it, which is/was 14 Sept 1752.  you could choose the "proleptic Gregorian" calendar, for example.

it would be a slick hack to make a text program pop up the correct GUI windows for UX.  if you make your functions/methods take optional arguments that pass to it callbacks to handle each discrete user interface and let the callback function given handle all input and output, then graceful GUI could be in its future.