- Correction for the Equation of Time
- Correction for Longitude
- Correction for Summer Time
These are considered in turn below:
Click the picture for more details!
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: |
Want a
little card to carry with you to help you check a sundial's
displayed time at ANY Longitude or Latitude in the British Isles? Hurry if you want one of the few remaining printed
versions... Click the picture for more details! |
|
Equation of Time Correction - 2012
© P.Powers 2011and 2012
The figures in the table below show more accurate figures in mins and secs by which a sundial should be corrected during December 2011 and the whole of 2012. 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 times other than Noon.
Negative values in the table indicate Dial Slow.
2012
| Jan 1 | -3m 19s | May 1 | 2m 57s | Sep 1 | 0m 7s | ||
| Jan 2 | -3m 47s | May 2 | 3m 4s | Sep 2 | 0m 27s | ||
| Jan 3 | -4m 15s | May 3 | 3m 10s | Sep 3 | 0m 46s | ||
| Jan 4 | -4m 43s | May 4 | 3m 16s | Sep 4 | 1m 6s | ||
| Jan 5 | -5m 10s | May 5 | 3m 20s | Sep 5 | 1m 26s | ||
| Jan 6 | -5m 36s | May 6 | 3m 25s | Sep 6 | 1m 46s | ||
| Jan 7 | -6m 3s | May 7 | 3m 29s | Sep 7 | 2m 7s | ||
| Jan 8 | -6m 28s | May 8 | 3m 32s | Sep 8 | 2m 27s | ||
| Jan 9 | -6m 54s | May 9 | 3m 35s | Sep 9 | 2m 48s | ||
| Jan 10 | -7m 18s | May 10 | 3m 37s | Sep 10 | 3m 9s | ||
| Jan 11 | -7m 43s | May 11 | 3m 38s | Sep 11 | 3m 30s | ||
| Jan 12 | -8m 6s | May 12 | 3m 39s | Sep 12 | 3m 51s | ||
| Jan 13 | -8m 29s | May 13 | 3m 40s | Sep 13 | 4m 13s | ||
| Jan 14 | -8m 52s | May 14 | 3m 39s | Sep 14 | 4m 34s | ||
| Jan 15 | -9m 14s | May 15 | 3m 39s | Sep 15 | 4m 55s | ||
| Jan 16 | -9m 35s | May 16 | 3m 37s | Sep 16 | 5m 17s | ||
| Jan 17 | -9m 55s | May 17 | 3m 36s | Sep 17 | 5m 38s | ||
| Jan 18 | -10m 15s | May 18 | 3m 33s | Sep 18 | 5m 59s | ||
| Jan 19 | -10m 34s | May 19 | 3m 30s | Sep 19 | 6m 21s | ||
| Jan 20 | -10m 52s | May 20 | 3m 27s | Sep 20 | 6m 42s | ||
| Jan 21 | -11m 10s | May 21 | 3m 23s | Sep 21 | 7m 3s | ||
| Jan 22 | -11m 27s | May 22 | 3m 18s | Sep 22 | 7m 25s | ||
| Jan 23 | -11m 43s | May 23 | 3m 13s | Sep 23 | 7m 46s | ||
| Jan 24 | -11m 58s | May 24 | 3m 7s | Sep 24 | 8m 7s | ||
| Jan 25 | -12m 13s | May 25 | 3m 1s | Sep 25 | 8m 27s | ||
| Jan 26 | -12m 26s | May 26 | 2m 55s | Sep 26 | 8m 48s | ||
| Jan 27 | -12m 39s | May 27 | 2m 48s | Sep 27 | 9m 8s | ||
| Jan 28 | -12m 51s | May 28 | 2m 40s | Sep 28 | 9m 29s | ||
| Jan 29 | -13m 3s | May 29 | 2m 32s | Sep 29 | 9m 49s | ||
| Jan 30 | -13m 13s | May 30 | 2m 24s | Sep 30 | 10m 8s | ||
| Jan 31 | -13m 23s | May 31 | 2m 15s | Oct 1 | 10m 28s | ||
| Feb 1 | -13m 32s | Jun 1 | 2m 6s | Oct 2 | 10m 47s | ||
| Feb 2 | -13m 40s | Jun 2 | 1m 56s | Oct 3 | 11m 6s | ||
| Feb 3 | -13m 47s | Jun 3 | 1m 46s | Oct 4 | 11m 24s | ||
| Feb 4 | -13m 53s | Jun 4 | 1m 36s | Oct 5 | 11m 42s | ||
| Feb 5 | -13m 59s | Jun 5 | 1m 25s | Oct 6 | 12m 0s | ||
| Feb 6 | -14m 4s | Jun 6 | 1m 15s | Oct 7 | 12m 18s | ||
| Feb 7 | -14m 7s | Jun 7 | 1m 3s | Oct 8 | 12m 34s | ||
| Feb 8 | -14m 11s | Jun 8 | 0m 52s | Oct 9 | 12m 51s | ||
| Feb 9 | -14m 13s | Jun 9 | 0m 40s | Oct 10 | 13m 7s | ||
| Feb 10 | -14m 14s | Jun 10 | 0m 28s | Oct 11 | 13m 23s | ||
| Feb 11 | -14m 15s | Jun 11 | 0m 16s | Oct 12 | 13m 38s | ||
| Feb 12 | -14m 15s | Jun 12 | 0m 3s | Oct 13 | 13m 52s | ||
| Feb 13 | -14m 14s | Jun 13 | -0m 9s | Oct 14 | 14m 6s | ||
| Feb 14 | -14m 13s | Jun 14 | -0m 22s | Oct 15 | 14m 20s | ||
| Feb 15 | -14m 10s | Jun 15 | -0m 35s | Oct 16 | 14m 33s | ||
| Feb 16 | -14m 7s | Jun 16 | -0m 48s | Oct 17 | 14m 45s | ||
| Feb 17 | -14m 4s | Jun 17 | -1m 0s | Oct 18 | 14m 57s | ||
| Feb 18 | -13m 59s | Jun 18 | -1m 14s | Oct 19 | 15m 8s | ||
| Feb 19 | -13m 54s | Jun 19 | -1m 27s | Oct 20 | 15m 18s | ||
| Feb 20 | -13m 48s | Jun 20 | -1m 40s | Oct 21 | 15m 28s | ||
| Feb 21 | -13m 41s | Jun 21 | -1m 53s | Oct 22 | 15m 37s | ||
| Feb 22 | -13m 34s | Jun 22 | -2m 6s | Oct 23 | 15m 46s | ||
| Feb 23 | -13m 26s | Jun 23 | -2m 19s | Oct 24 | 15m 53s | ||
| Feb 24 | -13m 18s | Jun 24 | -2m 31s | Oct 25 | 16m 0s | ||
| Feb 25 | -13m 9s | Jun 25 | -2m 44s | Oct 26 | 16m 7s | ||
| Feb 26 | -12m 59s | Jun 26 | -2m 57s | Oct 27 | 16m 12s | ||
| Feb 27 | -12m 49s | Jun 27 | -3m 9s | Oct 28 | 16m 17s | ||
| Feb 28 | -12m 38s | Jun 28 | -3m 21s | Oct 29 | 16m 21s | ||
| Feb 29 | -12m 27s | Jun 29 | -3m 33s | Oct 30 | 16m 24s | ||
| Mar 1 | -12m 15s | Jun 30 | -3m 45s | Oct 31 | 16m 26s | ||
| Mar 2 | -12m 3s | Jul 1 | -3m 57s | Nov 1 | 16m 28s | ||
| Mar 3 | -11m 50s | Jul 2 | -4m 8s | Nov 2 | 16m 29s | ||
| Mar 4 | -11m 37s | Jul 3 | -4m 19s | Nov 3 | 16m 29s | ||
| Mar 5 | -11m 23s | Jul 4 | -4m 30s | Nov 4 | 16m 28s | ||
| Mar 6 | -11m 9s | Jul 5 | -4m 40s | Nov 5 | 16m 26s | ||
| Mar 7 | -10m 55s | Jul 6 | -4m 50s | Nov 6 | 16m 23s | ||
| Mar 8 | -10m 40s | Jul 7 | -4m 60s | Nov 7 | 16m 20s | ||
| Mar 9 | -10m 25s | Jul 8 | -5m 9s | Nov 8 | 16m 16s | ||
| Mar 10 | -10m 9s | Jul 9 | -5m 18s | Nov 9 | 16m 11s | ||
| Mar 11 | -9m 53s | Jul 10 | -5m 26s | Nov 10 | 16m 5s | ||
| Mar 12 | -9m 37s | Jul 11 | -5m 34s | Nov 11 | 15m 58s | ||
| Mar 13 | -9m 21s | Jul 12 | -5m 42s | Nov 12 | 15m 50s | ||
| Mar 14 | -9m 4s | Jul 13 | -5m 49s | Nov 13 | 15m 41s | ||
| Mar 15 | -8m 47s | Jul 14 | -5m 55s | Nov 14 | 15m 32s | ||
| Mar 16 | -8m 30s | Jul 15 | -6m 1s | Nov 15 | 15m 22s | ||
| Mar 17 | -8m 12s | Jul 16 | -6m 7s | Nov 16 | 15m 10s | ||
| Mar 18 | -7m 55s | Jul 17 | -6m 12s | Nov 17 | 14m 58s | ||
| Mar 19 | -7m 37s | Jul 18 | -6m 16s | Nov 18 | 14m 46s | ||
| Mar 20 | -7m 20s | Jul 19 | -6m 20s | Nov 19 | 14m 32s | ||
| Mar 21 | -7m 2s | Jul 20 | -6m 24s | Nov 20 | 14m 17s | ||
| Mar 22 | -6m 44s | Jul 21 | -6m 27s | Nov 21 | 14m 2s | ||
| Mar 23 | -6m 26s | Jul 22 | -6m 29s | Nov 22 | 13m 46s | ||
| Mar 24 | -6m 7s | Jul 23 | -6m 30s | Nov 23 | 13m 29s | ||
| Mar 25 | -5m 49s | Jul 24 | -6m 31s | Nov 24 | 13m 11s | ||
| Mar 26 | -5m 31s | Jul 25 | -6m 32s | Nov 25 | 12m 53s | ||
| Mar 27 | -5m 13s | Jul 26 | -6m 32s | Nov 26 | 12m 34s | ||
| Mar 28 | -4m 55s | Jul 27 | -6m 31s | Nov 27 | 12m 14s | ||
| Mar 29 | -4m 37s | Jul 28 | -6m 30s | Nov 28 | 11m 54s | ||
| Mar 30 | -4m 19s | Jul 29 | -6m 28s | Nov 29 | 11m 32s | ||
| Mar 31 | -4m 1s | Jul 30 | -6m 25s | Nov 30 | 11m 10s | ||
| Apr 1 | -3m 43s | Jul 31 | -6m 22s | Dec 1 | 10m 48s | ||
| Apr 2 | -3m 26s | Aug 1 | -6m 18s | Dec 2 | 10m 25s | ||
| Apr 3 | -3m 8s | Aug 2 | -6m 14s | Dec 3 | 10m 1s | ||
| Apr 4 | -2m 51s | Aug 3 | -6m 9s | Dec 4 | 9m 37s | ||
| Apr 5 | -2m 34s | Aug 4 | -6m 4s | Dec 5 | 9m 12s | ||
| Apr 6 | -2m 17s | Aug 5 | -5m 57s | Dec 6 | 8m 46s | ||
| Apr 7 | -1m 60s | Aug 6 | -5m 51s | Dec 7 | 8m 20s | ||
| Apr 8 | -1m 43s | Aug 7 | -5m 43s | Dec 8 | 7m 54s | ||
| Apr 9 | -1m 27s | Aug 8 | -5m 35s | Dec 9 | 7m 27s | ||
| Apr 10 | -1m 11s | Aug 9 | -5m 27s | Dec 10 | 6m 60s | ||
| Apr 11 | -0m 55s | Aug 10 | -5m 18s | Dec 11 | 6m 32s | ||
| Apr 12 | -0m 40s | Aug 11 | -5m 8s | Dec 12 | 6m 4s | ||
| Apr 13 | -0m 25s | Aug 12 | -4m 58s | Dec 13 | 5m 36s | ||
| Apr 14 | -0m 10s | Aug 13 | -4m 47s | Dec 14 | 5m 7s | ||
| Apr 15 | 0m 5s | Aug 14 | -4m 36s | Dec 15 | 4m 38s | ||
| Apr 16 | 0m 19s | Aug 15 | -4m 24s | Dec 16 | 4m 9s | ||
| Apr 17 | 0m 32s | Aug 16 | -4m 12s | Dec 17 | 3m 40s | ||
| Apr 18 | 0m 46s | Aug 17 | -3m 59s | Dec 18 | 3m 11s | ||
| Apr 19 | 0m 58s | Aug 18 | -3m 45s | Dec 19 | 2m 41s | ||
| Apr 20 | 1m 11s | Aug 19 | -3m 31s | Dec 20 | 2m 11s | ||
| Apr 21 | 1m 23s | Aug 20 | -3m 17s | Dec 21 | 1m 42s | ||
| Apr 22 | 1m 35s | Aug 21 | -3m 2s | Dec 22 | 1m 12s | ||
| Apr 23 | 1m 46s | Aug 22 | -2m 47s | Dec 23 | 0m 42s | ||
| Apr 24 | 1m 56s | Aug 23 | -2m 31s | Dec 24 | 0m 12s | ||
| Apr 25 | 2m 7s | Aug 24 | -2m 15s | Dec 25 | -0m 17s | ||
| Apr 26 | 2m 16s | Aug 25 | -1m 59s | Dec 26 | -0m 47s | ||
| Apr 27 | 2m 26s | Aug 26 | -1m 42s | Dec 27 | -1m 16s | ||
| Apr 28 | 2m 34s | Aug 27 | -1m 24s | Dec 28 | -1m 46s | ||
| Apr 29 | 2m 43s | Aug 28 | -1m 7s | Dec 29 | -2m 15s | ||
| Apr 30 | 2m 50s | Aug 29 | -0m 49s | Dec 30 | -2m 43s | ||
| Aug 30 | -0m 30s | Dec 31 | -3m 12s | ||||
| Aug 31 | -0m 12s |
*[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 frequently accurate at worst to a second or two.]
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 corrected dial reading to obtain clock time.
Finally, how about a simple in-the-pocket card that allows you to check a dial at any Latitude or Longitude in the British Isles, by converting its Solar time to Clock time?
Click on the image below to find out how!
Go back to Sundials page?
31/12/2011