Thellid Leap Years

It's an insert rather than a "leap" but... I'll just go with the flow.

Here is a list of Thellid Leap Years from the surrounding 200 years. Note that Thellid Leap Years do not correspond to the customary Gregorian ones. Also note that these years are in Human Era (HE) format which prefixes a "1" to all modern dates. ie 12,000 HE is the Gregorian year 2,000.

It is easy to ascertain which years are Thellid Leap Years from a list of Greenwich Winter Solstice times in GMT standard. These occur when the solstice time first crosses from PM to AM. For example: the GWS in 2001 was at 7:21 PM on 21/12 but in 2002 it occurred at 1:14 AM on 22/12. Therefore 2002 is a Thellid Leap Year.

You will note that Thellid Leap Years mostly progress in jumps of 4 years, but about 3 times a century they jump 5. Each time a Leap Year is pushed back a year you lose ¼ of a leap day. This means that over a century you lose ¾ of a leap day and over 400 years you lose 3 leap days. This is because the solar year is not exactly 365¼ days but actually about 11 minutes shorter than that. Over 400 years this amounts to about 3 days, and these are the days lost by the occasional jump of 5 instead of 4.

The Gregorian Calendar loses 3 leap days over 400 years as well, but these are achieved by a leap year jump of 8 years at century boundaries 3 times out of 4. The Thellid and Gregorian Calendars both have 97 leap years in a 400 year period, so they both end up telling the same time. The difference is that the Thellid Calendar loses its leap days ¼ at a time every 33 years, whilst the Gregorian loses them in one chunk every 100 years, 3 centuries out of 4.

11900-11949	11950-11999	12000-12049	12050-12059
11903	11953	12002	12052
11908	11957	12006	12056
11912	11961	12011	12060
11916	11965	12015	12064
11920	11969	12019	12068
11924	11973	12023	12072
11928	11978	12027	12076
11932	11982	12031	12081
11936	11986	12035	12085
11941	11990	12039	12089
11945	11994	12043	12093
11949	11998	12048	12097