[Kstars-devel] KStars: trouble with the equinox calculation

[Heiko Evermann]

Hello everybody,

I just found the equinox calculator which seems to be quite nice. But 
unfortunately I cannot get the calculations done that I would like to do.

I am looking for the spring equinox dates and times for the years 25 to 35 AD. 
But when I insert e.g. 31 in the year box, what I get is the equinox for the 
year 2031. Even worse: for the year 999, I get the result for the equinox of 
2999. This offset calculation might make sense for a shortcut input of 7 for 
2007 but it means that I cannot get equinox dates before 1000 AD.

The mapping seems to be hidden somewhere deep in the code. 

It seems to work somehow in batch mode. With this input
25
26
27
28
29
30
31
32
33
34
35
1000
2005
2006
2007
-----
I get this output (with line breaks supplied to make the output readable in a 
mail program)25 24-01-17T06:46:11 524.519 
   25-06-24T19:14:11 92.4669 
   25-09-25T06:26:34 88.7026 
   25-12-22T23:18:19 -56.3554
26 25-10-27T14:46:35 240.432 
   26-06-25T01:08:04 92.4692 
   26-09-25T12:23:40 88.7017 
   26-12-23T05:14:11 -277.336
27 26-03-20T21:09:56 461.401 
   27-06-25T06:46:46 92.4769 
   27-09-25T18:13:26 88.7028 
   27-12-23T11:05:25 -307.673
28 27-02-18T18:56:00 491.739 
   28-06-24T12:40:37 92.4751 
   28-09-25T00:04:48 88.7042 
   28-12-22T16:58:47 17.0808
29 29-01-08T18:55:09 166.985 
   29-06-24T18:34:07 92.471 
   29-09-25T05:52:24 88.7077 
   29-12-22T22:51:30 -313.309
30 29-02-12T15:26:25 497.361 
   30-06-25T00:06:54 92.4767 
   30-09-25T11:33:19 88.7121 
   30-12-23T04:38:44 -247.603
31 30-04-19T14:09:45 431.658 
   31-06-25T05:56:49 92.4794 
   31-09-25T17:27:11 88.7063 
   31-12-23T10:24:11 -131.233
32 31-08-14T04:49:12 315.29 
   32-06-24T11:47:26 92.4755 
   32-09-24T23:12:11 88.7069 
   32-12-22T16:10:10 -318.074
33 32-02-08T14:23:45 502.131 
   33-06-24T17:32:04 92.4717 
   33-09-25T04:51:15 88.7124 
   33-12-22T21:57:11 -93.1946
34 33-09-20T17:16:59 277.255 
   34-06-24T23:24:16 92.4708 
   34-09-25T10:42:17 88.7122 
   34-12-23T03:47:48 -238.96
35 34-04-28T04:45:36 423.013 
   35-06-25T05:03:55 92.476 
   35-09-25T16:29:24 88.7095 
   35-12-23T09:31:01 -337.793
1000 1000-03-14T23:38:32 93.4488 
   1000-06-16T10:24:48 93.1483 
   1000-09-17T13:58:18 89.1817 
   1000-12-15T18:19:54 89.4663
2005 2005-03-20T12:25:28 92.7652 
   2005-06-21T06:47:18 93.6507 
   2005-09-22T22:24:22 89.8413 
   2005-12-21T18:35:51 88.991
2006 2006-03-20T18:22:54 92.7529 
   2006-06-21T12:27:02 93.6511 
   2006-09-23T04:04:35 89.8461 
   2006-12-22T00:23:00 91.8929
2007 2007-03-23T21:48:50 89.8464 
   2007-06-21T18:07:36 93.6561 
   2007-09-23T09:52:26 89.8446 
   2007-12-22T06:08:43 88.9749
--------
Now this looks a bit wierd.
25 24-01-17T06:46:11 524.519 
would imply that the spring equinox in the year 25 already took place in the 
year before, in January!!

Is there a way to fix this? And (in case this is difficult), where can I get a 
table of the spring equinox dates for the years 25 to 35?
And how precise is this calculation in KStars for dates that long ago?

Kind regards and thanks for your help,

Heiko Evermann