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"Time and Tide" Sundial
Fort George interactive sundial
Fort George interactive sundial

Scale of Dates

Instrucion Plaque
Instruction Plaque

The Fort George interactive sundial is to be found embedded in the sandstone deck of the refurbished jetty on the banks of the river Foyle near the Sainsbury's supermarket in Derry City.

Sundials come in a wide range of different types with the 'garden' variety being the most common, but the most popular for parks and public areas is the interactive sundial which uses a person's own shadow to show the time. They make an unusual conversation piece with the obvious novelty of the user being a part of the sundial. Fascinating for both adults and children they have the additional advantage that they cannot be easily stolen, or damaged by vandals and indicate the correct solar time all year round.

The sun reaches its highest point above the horizon at noon at all places along the same North/South line of longitude and our sundial reads 12 o'clock at this time. It follows that at that instant in places to the east of the dial noon has already passed, and in places to the west noon has not yet arrived. There is one hour of time difference for every 15 degrees of longitude difference. When it is solar noon at Greenwich, in places in Ireland 7 degrees 30 minutes west of Greenwich it is 11:30 A.M. sun time.

The solar day varies from 20 secs less than the 24 hrs average day length we use for our clocks to 30 secs more. These small time differences accumulate over a period of months to reach a total of just over 14 minutes in mid-February, when "sundial time" is slow relative to "clock time", and to just over 16 minutes difference at the beginning of November, when "sundial time" is fast relative to "clock time". The total difference between sun time and watch time for each month is shown on the instruction plaque located in the centre of the dial.

For a full description of the difference between suntime and clock time click on this link

A person's height does not affect the time because it is the direction of their shadow which indicates the time, not its length. Equally suitable for use by small children as well as larger adults, young children can simply join their hands together over their head - this will increase the length of their shadow, and bring it much nearer to the hour markers.

The origin of the motto "Time and Tide waits for no one" is uncertain, although it's clear that the phrase is ancient and alludes to the fact that human events or concerns cannot stop the passage of time or the movement of the tides. It exhorts us to remember that we should use our time well without procrastination or delay.

The 'Time and Tide' sundial invites participation from the public with the sun tracking the person's shadow between 4 a.m. in the morning to 8 p.m. in the evening (solar times).

Lat 55° 1' North  Long 7° 19' West

Irish Grid  C   244085   418445

If you know the location of a sundial in Ireland (NOT a mass produced DIY Store garden ornament) please email it to me (Click here to email M.J.Harley) - a member of British Sundial Society
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