Dial Time Corrections
Corrections need to be made in order to obtain Mean time from a sundial. These are:
These are considered in turn below:
Equation of Time Correction - 2009
© P.Powers 2009
The figures in the table below show more accurate figures in mins and secs by which a sundial should be corrected during the current year. The figures represent the Equation of Time at 12Hrs (Noon) GMT on the date stated and are calculated using the method after Smart. Interpolation may be necessary if an accurate EoT is needed for other times.
Negative values in the list indicate Dial Slow.
2009
Jan 1 -3m 40.0s Jan 2 -4m 7.9s Jan 3 -4m 35.5s Jan 4 -5m 2.7s Jan 5 -5m 29.6s Jan 6 -5m 55.9s Jan 7 -6m 21.9s Jan 8 -6m 47.3s Jan 9 -7m 12.2s Jan 10 -7m 36.5s Jan 11 -8m 0.4s Jan 12 -8m 23.5s Jan 13 -8m 46.2s Jan 14 -9m 8.1s Jan 15 -9m 29.4s Jan 16 -9m 50.1s Jan 17 -10m 10.0s Jan 18 -10m 29.3s Jan 19 -10m 47.8s Jan 20 -11m 5.6s Jan 21 -11m 22.6s Jan 22 -11m 38.9s Jan 23 -11m 54.4s Jan 24 -12m 9.1s Jan 25 -12m 23.1s Jan 26 -12m 36.2s Jan 27 -12m 48.6s Jan 28 -13m 0.1s Jan 29 -13m 10.8s Jan 30 -13m 20.7s Jan 31 -13m 29.7s Feb 1 -13m 38.0s Feb 2 -13m 45.4s Feb 3 -13m 52.0s Feb 4 -13m 57.7s Feb 5 -14m 2.7s Feb 6 -14m 6.8s Feb 7 -14m 10.2s Feb 8 -14m 12.7s Feb 9 -14m 14.4s Feb 10 -14m 15.4s Feb 11 -14m 15.5s Feb 12 -14m 14.9s Feb 13 -14m 13.5s Feb 14 -14m 11.4s Feb 15 -14m 8.5s Feb 16 -14m 4.9s Feb 17 -14m 0.6s Feb 18 -13m 55.6s Feb 19 -13m 49.9s Feb 20 -13m 43.6s Feb 21 -13m 36.5s Feb 22 -13m 28.9s Feb 23 -13m 20.6s Feb 24 -13m 11.7s Feb 25 -13m 2.2s Feb 26 -12m 52.1s Feb 27 -12m 41.5s Feb 28 -12m 30.4s Feb 29 -12m 18.7s Mar 1 -12m 18.7s Mar 2 -12m 6.5s Mar 3 -11m 53.9s Mar 4 -11m 40.8s Mar 5 -11m 27.2s Mar 6 -11m 13.2s Mar 7 -10m 58.8s Mar 8 -10m 44.1s Mar 9 -10m 28.9s Mar 10 -10m 13.5s Mar 11 -9m 57.7s Mar 12 -9m 41.6s Mar 13 -9m 25.2s Mar 14 -9m 8.6s Mar 15 -8m 51.7s Mar 16 -8m 34.6s Mar 17 -8m 17.4s Mar 18 -7m 59.9s Mar 19 -7m 42.3s Mar 20 -7m 24.5s Mar 21 -7m 6.7s Mar 22 -6m 48.7s Mar 23 -6m 30.7s Mar 24 -6m 12.6s Mar 25 -5m 54.4s Mar 26 -5m 36.3s Mar 27 -5m 18.2s Mar 28 -5m 0.0s Mar 29 -4m 42.0s Mar 30 -4m 24.0s Mar 31 -4m 6.0s Apr 1 -3m 48.2s Apr 2 -3m 30.5s Apr 3 -3m 12.9s Apr 4 -2m 55.5s Apr 5 -2m 38.3s Apr 6 -2m 21.2s Apr 7 -2m 4.4s Apr 8 -1m 47.8s Apr 9 -1m 31.4s Apr 10 -1m 15.3s Apr 11 -0m 59.5s Apr 12 -0m 44.0s Apr 13 -0m 28.8s Apr 14 -0m 13.9s Apr 15 0m 0.6s Apr 16 0m 14.8s Apr 17 0m 28.6s Apr 18 0m 42.0s Apr 19 0m 55.1s Apr 20 1m 7.7s Apr 21 1m 19.8s Apr 22 1m 31.6s Apr 23 1m 42.9s Apr 24 1m 53.7s Apr 25 2m 4.0s Apr 26 2m 13.9s Apr 27 2m 23.3s Apr 28 2m 32.1s Apr 29 2m 40.5s Apr 30 2m 48.3s May 1 2m 55.6s May 2 3m 2.4s May 3 3m 8.6s May 4 3m 14.2s May 5 3m 19.3s May 6 3m 23.9s May 7 3m 27.9s May 8 3m 31.3s May 9 3m 34.1s May 10 3m 36.4s May 11 3m 38.1s May 12 3m 39.2s May 13 3m 39.8s May 14 3m 39.8s May 15 3m 39.2s May 16 3m 38.1s May 17 3m 36.4s May 18 3m 34.1s May 19 3m 31.3s May 20 3m 28.0s May 21 3m 24.1s May 22 3m 19.7s May 23 3m 14.8s May 24 3m 9.3s May 25 3m 3.4s May 26 2m 56.9s May 27 2m 50.0s May 28 2m 42.7s May 29 2m 34.8s May 30 2m 26.6s May 31 2m 17.9s Jun 1 2m 8.8s Jun 2 1m 59.4s Jun 3 1m 49.5s Jun 4 1m 39.3s Jun 5 1m 28.8s Jun 6 1m 17.9s Jun 7 1m 6.8s Jun 8 0m 55.4s Jun 9 0m 43.7s Jun 10 0m 31.7s Jun 11 0m 19.6s Jun 12 0m 7.3s Jun 13 -0m 5.2s Jun 14 -0m 17.9s Jun 15 -0m 30.6s Jun 16 -0m 43.5s Jun 17 -0m 56.5s Jun 18 -1m 9.5s Jun 19 -1m 22.6s Jun 20 -1m 35.6s Jun 21 -1m 48.7s Jun 22 -2m 1.7s Jun 23 -2m 14.6s Jun 24 -2m 27.5s Jun 25 -2m 40.2s Jun 26 -2m 52.9s Jun 27 -3m 5.3s Jun 28 -3m 17.6s Jun 29 -3m 29.7s Jun 30 -3m 41.6s Jul 1 -3m 53.2s Jul 2 -4m 4.6s Jul 3 -4m 15.7s Jul 4 -4m 26.4s Jul 5 -4m 36.9s Jul 6 -4m 47.0s Jul 7 -4m 56.7s Jul 8 -5m 6.1s Jul 9 -5m 15.0s Jul 10 -5m 23.5s Jul 11 -5m 31.6s Jul 12 -5m 39.3s Jul 13 -5m 46.4s Jul 14 -5m 53.1s Jul 15 -5m 59.3s Jul 16 -6m 5.0s Jul 17 -6m 10.1s Jul 18 -6m 14.8s Jul 19 -6m 18.9s Jul 20 -6m 22.4s Jul 21 -6m 25.4s Jul 22 -6m 27.8s Jul 23 -6m 29.6s Jul 24 -6m 30.8s Jul 25 -6m 31.5s Jul 26 -6m 31.5s Jul 27 -6m 31.0s Jul 28 -6m 29.8s Jul 29 -6m 28.1s Jul 30 -6m 25.7s Jul 31 -6m 22.7s Aug 1 -6m 19.2s Aug 2 -6m 15.0s Aug 3 -6m 10.2s Aug 4 -6m 4.8s Aug 5 -5m 58.8s Aug 6 -5m 52.2s Aug 7 -5m 45.0s Aug 8 -5m 37.2s Aug 9 -5m 28.9s Aug 10 -5m 19.9s Aug 11 -5m 10.4s Aug 12 -5m 0.4s Aug 13 -4m 49.8s Aug 14 -4m 38.6s Aug 15 -4m 26.9s Aug 16 -4m 14.7s Aug 17 -4m 1.9s Aug 18 -3m 48.7s Aug 19 -3m 35.0s Aug 20 -3m 20.7s Aug 21 -3m 6.1s Aug 22 -2m 50.9s Aug 23 -2m 35.3s Aug 24 -2m 19.3s Aug 25 -2m 2.9s Aug 26 -1m 46.1s Aug 27 -1m 28.9s Aug 28 -1m 11.3s Aug 29 -0m 53.4s Aug 30 -0m 35.1s Aug 31 -0m 16.5s Sep 1 0m 2.4s Sep 2 0m 21.6s Sep 3 0m 41.1s Sep 4 1m 0.8s Sep 5 1m 20.7s Sep 6 1m 40.9s Sep 7 2m 1.3s Sep 8 2m 21.9s Sep 9 2m 42.6s Sep 10 3m 3.5s Sep 11 3m 24.5s Sep 12 3m 45.6s Sep 13 4m 6.9s Sep 14 4m 28.1s Sep 15 4m 49.5s Sep 16 5m 10.9s Sep 17 5m 32.3s Sep 18 5m 53.7s Sep 19 6m 15.1s Sep 20 6m 36.4s Sep 21 6m 57.7s Sep 22 7m 18.8s Sep 23 7m 39.9s Sep 24 8m 0.9s Sep 25 8m 21.7s Sep 26 8m 42.3s Sep 27 9m 2.8s Sep 28 9m 23.1s Sep 29 9m 43.1s Sep 30 10m 2.9s Oct 1 10m 22.4s Oct 2 10m 41.6s Oct 3 11m 0.6s Oct 4 11m 19.2s Oct 5 11m 37.4s Oct 6 11m 55.3s Oct 7 12m 12.8s Oct 8 12m 29.8s Oct 9 12m 46.5s Oct 10 13m 2.7s Oct 11 13m 18.4s Oct 12 13m 33.6s Oct 13 13m 48.4s Oct 14 14m 2.6s Oct 15 14m 16.2s Oct 16 14m 29.3s Oct 17 14m 41.8s Oct 18 14m 53.6s Oct 19 15m 4.9s Oct 20 15m 15.5s Oct 21 15m 25.5s Oct 22 15m 34.8s Oct 23 15m 43.4s Oct 24 15m 51.3s Oct 25 15m 58.5s Oct 26 16m 5.0s Oct 27 16m 10.7s Oct 28 16m 15.6s Oct 29 16m 19.8s Oct 30 16m 23.2s Oct 31 16m 25.7s Nov 1 16m 27.5s Nov 2 16m 28.5s Nov 3 16m 28.6s Nov 4 16m 28.0s Nov 5 16m 26.4s Nov 6 16m 24.1s Nov 7 16m 20.8s Nov 8 16m 16.8s Nov 9 16m 11.8s Nov 10 16m 6.0s Nov 11 15m 59.4s Nov 12 15m 51.9s Nov 13 15m 43.5s Nov 14 15m 34.3s Nov 15 15m 24.2s Nov 16 15m 13.2s Nov 17 15m 1.5s Nov 18 14m 48.9s Nov 19 14m 35.4s Nov 20 14m 21.2s Nov 21 14m 6.1s Nov 22 13m 50.2s Nov 23 13m 33.5s Nov 24 13m 16.1s Nov 25 12m 57.9s Nov 26 12m 39.0s Nov 27 12m 19.3s Nov 28 11m 58.9s Nov 29 11m 37.9s Nov 30 11m 16.1s Dec 1 10m 53.7s Dec 2 10m 30.7s Dec 3 10m 7.1s Dec 4 9m 42.9s Dec 5 9m 18.1s Dec 6 8m 52.9s Dec 7 8m 27.1s Dec 8 8m 0.8s Dec 9 7m 34.1s Dec 10 7m 6.9s Dec 11 6m 39.4s Dec 12 6m 11.5s Dec 13 5m 43.3s Dec 14 5m 14.8s Dec 15 4m 46.0s Dec 16 4m 16.9s Dec 17 3m 47.7s Dec 18 3m 18.3s Dec 19 2m 48.7s Dec 20 2m 19.1s Dec 21 1m 49.4s Dec 22 1m 19.6s Dec 23 0m 49.8s Dec 24 0m 20.1s Dec 25 -0m 9.6s Dec 26 -0m 39.2s Dec 27 -1m 8.7s Dec 28 -1m 38.0s Dec 29 -2m 7.1s Dec 30 -2m 36.0s Dec 31 -3m 4.7s [NB. In non-leap years the entry for Feb 29 will be the same as that for Mar 1st. The above EoT figures are calculated using Meeus's medium accuracy formula (after Smart) and some may occasionally be stated to a precision greater than their accuracy. They are accurate at worst to a few seconds - often much better.]
Correction for Longitude
When a dial is not on the local Time Meridian, for example for a dial in the UK that is not on the actual Greenwich Meridian, then the sun is overhead at the dial at a time earlier or later than at Greenwich. The correction to be made is 4 minutes of time for every degree of longitude difference from Greenwich. This figure should be subtracted from the dial reading for dials East of Greenwich (Such dials are Fast) and added for dials West of Greenwich. (Such dials are Slow).
Correction for Summer Time
Finally during the period when Summer Time (Daylight Saving Time) is in force one hour should be added to the dial reading to obtain clock time.
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02/04/08