THE DURATION OF THE TRUE SOLAR DAY

The interval of the time between two consecutive transits of the center of the Sun trough the meridian of a given place is called a true solar day. This interval is not constant but varies between 23h59m39s and 24h0m30s, with the present values of the obliquity of the ecliptic, the eccentricity of the terrestrial orbit and the perigee's longitude. The cause of the variation is the inconstant speed of the Sun along the ecliptic. The lenght of the true solar day is 24 hour only when the variation of the equation of time is zero, and not when the same equation is zero.

Day Transit Duration 01-jan-09 12:13:39 02-jan-09 12:14:07 1.000324 03-jan-09 12:14:35 1.000324 04-jan-09 12:15:02 1.000313 05-jan-09 12:15:29 1.000313 06-jan-09 12:15:55 1.000301 07-jan-09 12:16:21 1.000301 08-jan-09 12:16:47 1.000301 09-jan-09 12:17:12 1.000289 10-jan-09 12:17:36 1.000278 11-jan-09 12:18:00 1.000278 12-jan-09 12:18:23 1.000266 13-jan-09 12:18:45 1.000255 14-jan-09 12:19:07 1.000255 15-jan-09 12:19:28 1.000243 16-jan-09 12:19:49 1.000243 17-jan-09 12:20:09 1.000231 18-jan-09 12:20:28 1.000220 19-jan-09 12:20:46 1.000208 20-jan-09 12:21:04 1.000208 21-jan-09 12:21:21 1.000197 22-jan-09 12:21:38 1.000197 23-jan-09 12:21:53 1.000174 24-jan-09 12:22:08 1.000174 25-jan-09 12:22:22 1.000162 26-jan-09 12:22:35 1.000150 27-jan-09 12:22:47 1.000139 28-jan-09 12:22:59 1.000139 29-jan-09 12:23:10 1.000127 30-jan-09 12:23:19 1.000104 31-jan-09 12:23:28 1.000104 01-feb-09 12:23:37 1.000104 02-feb-09 12:23:44 1.000081 03-feb-09 12:23:51 1.000081 04-feb-09 12:23:56 1.000058 05-feb-09 12:24:01 1.000058 06-feb-09 12:24:05 1.000046 07-feb-09 12:24:09 1.000046 08-feb-09 12:24:11 1.000023 09-feb-09 12:24:13 1.000023 10-feb-09 12:24:14 1.000012 11-feb-09 12:24:14 1.000000 12-feb-09 12:24:13 0.999988 13-feb-09 12:24:12 0.999988 14-feb-09 12:24:10 0.999977 15-feb-09 12:24:07 0.999965 16-feb-09 12:24:03 0.999954 17-feb-09 12:23:59 0.999954 18-feb-09 12:23:54 0.999942 19-feb-09 12:23:49 0.999942 20-feb-09 12:23:42 0.999919 21-feb-09 12:23:35 0.999919 22-feb-09 12:23:28 0.999919 23-feb-09 12:23:20 0.999907 24-feb-09 12:23:11 0.999896 25-feb-09 12:23:02 0.999896 26-feb-09 12:22:52 0.999884 27-feb-09 12:22:42 0.999884 28-feb-09 12:22:31 0.999873 01-mar-09 12:22:19 0.999861 02-mar-09 12:22:07 0.999861 03-mar-09 12:21:55 0.999861 04-mar-09 12:21:42 0.999850 05-mar-09 12:21:28 0.999838 06-mar-09 12:21:14 0.999838 07-mar-09 12:21:00 0.999838 08-mar-09 12:20:45 0.999826 09-mar-09 12:20:30 0.999826 10-mar-09 12:20:15 0.999826 11-mar-09 12:19:59 0.999815 12-mar-09 12:19:43 0.999815 13-mar-09 12:19:27 0.999815 14-mar-09 12:19:10 0.999803 15-mar-09 12:18:53 0.999803 16-mar-09 12:18:36 0.999803 17-mar-09 12:18:19 0.999803 18-mar-09 12:18:02 0.999803 19-mar-09 12:17:44 0.999792 20-mar-09 12:17:26 0.999792 21-mar-09 12:17:08 0.999792 22-mar-09 12:16:51 0.999803 23-mar-09 12:16:33 0.999792 24-mar-09 12:16:15 0.999792 25-mar-09 12:15:57 0.999792 26-mar-09 12:15:38 0.999780 27-mar-09 12:15:20 0.999792 28-mar-09 12:15:02 0.999792 29-mar-09 12:14:44 0.999792 30-mar-09 12:14:26 0.999792 31-mar-09 12:14:08 0.999792 01-apr-09 12:13:51 0.999803 02-apr-09 12:13:33 0.999792 03-apr-09 12:13:15 0.999792 04-apr-09 12:12:58 0.999803 05-apr-09 12:12:40 0.999792 06-apr-09 12:12:23 0.999803 07-apr-09 12:12:06 0.999803 08-apr-09 12:11:50 0.999815 09-apr-09 12:11:33 0.999803 10-apr-09 12:11:17 0.999815 11-apr-09 12:11:01 0.999815 12-apr-09 12:10:45 0.999815 13-apr-09 12:10:30 0.999826 14-apr-09 12:10:15 0.999826 15-apr-09 12:10:00 0.999826 16-apr-09 12:09:46 0.999838 17-apr-09 12:09:32 0.999838 18-apr-09 12:09:19 0.999850 19-apr-09 12:09:05 0.999838 20-apr-09 12:08:53 0.999861 21-apr-09 12:08:41 0.999861 22-apr-09 12:08:29 0.999861 23-apr-09 12:08:18 0.999873 24-apr-09 12:08:07 0.999873 25-apr-09 12:07:57 0.999884 26-apr-09 12:07:47 0.999884 27-apr-09 12:07:37 0.999884 28-apr-09 12:07:29 0.999907 29-apr-09 12:07:20 0.999896 30-apr-09 12:07:12 0.999907 01-may-09 12:07:05 0.999919 02-may-09 12:06:58 0.999919 03-may-09 12:06:52 0.999931 04-may-09 12:06:46 0.999931 05-may-09 12:06:41 0.999942 06-may-09 12:06:36 0.999942 07-may-09 12:06:32 0.999954 08-may-09 12:06:29 0.999965 09-may-09 12:06:26 0.999965 10-may-09 12:06:23 0.999965 11-may-09 12:06:21 0.999977 12-may-09 12:06:20 0.999988 13-may-09 12:06:20 1.000000 14-may-09 12:06:19 0.999988 15-may-09 12:06:20 1.000012 16-may-09 12:06:21 1.000012 17-may-09 12:06:23 1.000023 18-may-09 12:06:25 1.000023 19-may-09 12:06:28 1.000035 20-may-09 12:06:31 1.000035 21-may-09 12:06:35 1.000046 22-may-09 12:06:40 1.000058 23-may-09 12:06:45 1.000058 24-may-09 12:06:50 1.000058 25-may-09 12:06:56 1.000069 26-may-09 12:07:03 1.000081 27-may-09 12:07:10 1.000081 28-may-09 12:07:17 1.000081 29-may-09 12:07:25 1.000093 30-may-09 12:07:33 1.000093 31-may-09 12:07:42 1.000104 01-jun-09 12:07:51 1.000104 02-jun-09 12:08:00 1.000104 03-jun-09 12:08:10 1.000116 04-jun-09 12:08:20 1.000116 05-jun-09 12:08:31 1.000127 06-jun-09 12:08:41 1.000116 07-jun-09 12:08:53 1.000139 08-jun-09 12:09:04 1.000127 09-jun-09 12:09:16 1.000139 10-jun-09 12:09:27 1.000127 11-jun-09 12:09:39 1.000139 12-jun-09 12:09:52 1.000150 13-jun-09 12:10:04 1.000139 14-jun-09 12:10:17 1.000150 15-jun-09 12:10:30 1.000150 16-jun-09 12:10:43 1.000150 17-jun-09 12:10:56 1.000150 18-jun-09 12:11:09 1.000150 19-jun-09 12:11:22 1.000150 20-jun-09 12:11:35 1.000150 21-jun-09 12:11:48 1.000150 22-jun-09 12:12:01 1.000150 23-jun-09 12:12:14 1.000150 24-jun-09 12:12:27 1.000150 25-jun-09 12:12:40 1.000150 26-jun-09 12:12:53 1.000150 27-jun-09 12:13:05 1.000139 28-jun-09 12:13:18 1.000150 29-jun-09 12:13:30 1.000139 30-jun-09 12:13:42 1.000139 01-jul-09 12:13:53 1.000127 02-jul-09 12:14:05 1.000139 03-jul-09 12:14:16 1.000127 04-jul-09 12:14:27 1.000127 05-jul-09 12:14:37 1.000116 06-jul-09 12:14:47 1.000116 07-jul-09 12:14:57 1.000116 08-jul-09 12:15:06 1.000104 09-jul-09 12:15:15 1.000104 10-jul-09 12:15:23 1.000093 11-jul-09 12:15:31 1.000093 12-jul-09 12:15:39 1.000093 13-jul-09 12:15:46 1.000081 14-jul-09 12:15:53 1.000081 15-jul-09 12:15:59 1.000069 16-jul-09 12:16:05 1.000069 17-jul-09 12:16:10 1.000058 18-jul-09 12:16:15 1.000058 19-jul-09 12:16:19 1.000046 20-jul-09 12:16:22 1.000035 21-jul-09 12:16:25 1.000035 22-jul-09 12:16:28 1.000035 23-jul-09 12:16:30 1.000023 24-jul-09 12:16:31 1.000012 25-jul-09 12:16:32 1.000012 26-jul-09 12:16:32 1.000000 27-jul-09 12:16:32 1.000000 28-jul-09 12:16:31 0.999988 29-jul-09 12:16:29 0.999977 30-jul-09 12:16:26 0.999965 31-jul-09 12:16:24 0.999977 01-aug-09 12:16:20 0.999954 02-aug-09 12:16:16 0.999954 03-aug-09 12:16:11 0.999942 04-aug-09 12:16:05 0.999931 05-aug-09 12:15:59 0.999931 06-aug-09 12:15:53 0.999931 07-aug-09 12:15:45 0.999907 08-aug-09 12:15:38 0.999919 09-aug-09 12:15:29 0.999896 10-aug-09 12:15:20 0.999896 11-aug-09 12:15:11 0.999896 12-aug-09 12:15:01 0.999884 13-aug-09 12:14:50 0.999873 14-aug-09 12:14:39 0.999873 15-aug-09 12:14:27 0.999861 16-aug-09 12:14:15 0.999861 17-aug-09 12:14:02 0.999850 18-aug-09 12:13:49 0.999850 19-aug-09 12:13:36 0.999850 20-aug-09 12:13:21 0.999826 21-aug-09 12:13:07 0.999838 22-aug-09 12:12:52 0.999826 23-aug-09 12:12:36 0.999815 24-aug-09 12:12:20 0.999815 25-aug-09 12:12:04 0.999815 26-aug-09 12:11:47 0.999803 27-aug-09 12:11:30 0.999803 28-aug-09 12:11:12 0.999792 29-aug-09 12:10:54 0.999792 30-aug-09 12:10:36 0.999792 31-aug-09 12:10:17 0.999780 01-sep-09 12:09:58 0.999780 02-sep-09 12:09:39 0.999780 03-sep-09 12:09:19 0.999769 04-sep-09 12:08:59 0.999769 05-sep-09 12:08:39 0.999769 06-sep-09 12:08:19 0.999769 07-sep-09 12:07:59 0.999769 08-sep-09 12:07:38 0.999757 09-sep-09 12:07:17 0.999757 10-sep-09 12:06:56 0.999757 11-sep-09 12:06:35 0.999757 12-sep-09 12:06:14 0.999757 13-sep-09 12:05:53 0.999757 14-sep-09 12:05:31 0.999745 15-sep-09 12:05:10 0.999757 16-sep-09 12:04:49 0.999757 17-sep-09 12:04:27 0.999745 18-sep-09 12:04:06 0.999757 19-sep-09 12:03:45 0.999757 20-sep-09 12:03:23 0.999745 21-sep-09 12:03:02 0.999757 22-sep-09 12:02:41 0.999757 23-sep-09 12:02:20 0.999757 24-sep-09 12:01:59 0.999757 25-sep-09 12:01:38 0.999757 26-sep-09 12:01:18 0.999769 27-sep-09 12:00:57 0.999757 28-sep-09 12:00:37 0.999769 29-sep-09 12:00:17 0.999769 30-sep-09 11:59:58 0.999780 01-oct-09 11:59:38 0.999769 02-oct-09 11:59:19 0.999780 03-oct-09 11:59:00 0.999780 04-oct-09 11:58:41 0.999780 05-oct-09 11:58:23 0.999792 06-oct-09 11:58:05 0.999792 07-oct-09 11:57:48 0.999803 08-oct-09 11:57:31 0.999803 09-oct-09 11:57:14 0.999803 10-oct-09 11:56:58 0.999815 11-oct-09 11:56:43 0.999826 12-oct-09 11:56:28 0.999826 13-oct-09 11:56:13 0.999826 14-oct-09 11:55:59 0.999838 15-oct-09 11:55:46 0.999850 16-oct-09 11:55:33 0.999850 17-oct-09 11:55:20 0.999850 18-oct-09 11:55:09 0.999873 19-oct-09 11:54:58 0.999873 20-oct-09 11:54:47 0.999873 21-oct-09 11:54:37 0.999884 22-oct-09 11:54:28 0.999896 23-oct-09 11:54:20 0.999907 24-oct-09 11:54:12 0.999907 25-oct-09 11:54:05 0.999919 26-oct-09 11:53:59 0.999931 27-oct-09 11:53:53 0.999931 28-oct-09 11:53:48 0.999942 29-oct-09 11:53:44 0.999954 30-oct-09 11:53:40 0.999954 31-oct-09 11:53:38 0.999977 01-nov-09 11:53:36 0.999977 02-nov-09 11:53:35 0.999988 03-nov-09 11:53:34 0.999988 04-nov-09 11:53:35 1.000012 05-nov-09 11:53:36 1.000012 06-nov-09 11:53:38 1.000023 07-nov-09 11:53:41 1.000035 08-nov-09 11:53:45 1.000046 09-nov-09 11:53:50 1.000058 10-nov-09 11:53:56 1.000069 11-nov-09 11:54:02 1.000069 12-nov-09 11:54:10 1.000093 13-nov-09 11:54:18 1.000093 14-nov-09 11:54:27 1.000104 15-nov-09 11:54:37 1.000116 16-nov-09 11:54:48 1.000127 17-nov-09 11:55:00 1.000139 18-nov-09 11:55:12 1.000139 19-nov-09 11:55:25 1.000150 20-nov-09 11:55:39 1.000162 21-nov-09 11:55:54 1.000174 22-nov-09 11:56:10 1.000185 23-nov-09 11:56:27 1.000197 24-nov-09 11:56:44 1.000197 25-nov-09 11:57:02 1.000208 26-nov-09 11:57:20 1.000208 27-nov-09 11:57:40 1.000231 28-nov-09 11:58:00 1.000231 29-nov-09 11:58:21 1.000243 30-nov-09 11:58:42 1.000243 01-dec-09 11:59:04 1.000255 02-dec-09 11:59:27 1.000266 03-dec-09 11:59:51 1.000278 04-dec-09 12:00:15 1.000278 05-dec-09 12:00:39 1.000278 06-dec-09 12:01:04 1.000289 07-dec-09 12:01:30 1.000301 08-dec-09 12:01:56 1.000301 09-dec-09 12:02:23 1.000313 10-dec-09 12:02:50 1.000313 11-dec-09 12:03:17 1.000313 12-dec-09 12:03:45 1.000324 13-dec-09 12:04:14 1.000336 14-dec-09 12:04:42 1.000324 15-dec-09 12:05:11 1.000336 16-dec-09 12:05:40 1.000336 17-dec-09 12:06:10 1.000347 18-dec-09 12:06:39 1.000336 19-dec-09 12:07:09 1.000347 20-dec-09 12:07:39 1.000347 21-dec-09 12:08:09 1.000347 22-dec-09 12:08:39 1.000347 23-dec-09 12:09:08 1.000336 24-dec-09 12:09:38 1.000347 25-dec-09 12:10:08 1.000347 26-dec-09 12:10:38 1.000347 27-dec-09 12:11:07 1.000336 28-dec-09 12:11:36 1.000336 29-dec-09 12:12:06 1.000347 30-dec-09 12:12:34 1.000324 31-dec-09 12:13:03 1.000336 The graph shows the duration of the true solar day during year 2009