Under the eye of the clock

Jenny Beale woke up one morning with an 'order' in her head. The result was a spiritual sanctuary containing the country's largest sundial, writes Lorna Siggins.

Jenny Beale believes that one of the equinoxes - the two times a year every place on Earth has a 12-hour day - should be named world peace day. "Spring or autumn, it is the one time of the year when the whole world is having the same experience."

How does she know this? Because it is defined by the only straight limestone line on the newly constructed, largest sundial in Ireland.

Delicate petals, defined curves and beautifully carved numbers and dates mark out the extraordinarily large orb in the lee of an esker which Beale and her husband, Dr Colin Brown, have created at Brigit's Garden in Roscahill, Co Galway. Not only is it a natural clock, but it is also a calendar which sets the date from the sun's shadow. Casting the shadow is a still and stern spike of oak which had been preserved for several thousands of years in a Co Tipperary bog.

Known as a "gnomon", the spike was carved by sculptor Ronnie Graham and its precise position toward the southern end of the circle was carefully calculated, using an Ordnance Survey 1:50,000 Discovery series map and a Global Positioning System (GPS) satellite receiver. This determined that it had to be set at 53 degrees 22.85676 minutes north and 9 degrees 12.79546 minutes west respectively to define the dial's limits. Dr Brown knows the "lat/long" almost off by heart, because he has spent hours on computers and out in the elements with distance-measuring instruments, along with fellow expert Maire Cris Ní Chionna of Galway County Council.

It was about six years ago, when Beale was still laying out her wonderful landscape in Roscahill, that the sundial was conceived. The English couple had moved to Galway some 20 years previously, with Dr Brown attached to what is now NUI Galway's Department of Earth and Ocean Sciences and Beale busy rearing their three children. When she was left a bequest, she bought three lots of farmland in Roscahill beyond Moycullen - rock, soil and meadow incorporating a fairy fort, natural woodland and a "lochan" or lake. She knew what she wanted to do with it, having woken up one morning with an "order" in her head. Samhain, Imbolc, Bealtaine, Lughnasa, the four Celtic festivals of the seasons, form the nucleus of a spiritual sanctuary, designed with 2002 Chelsea flower show winner Mary Reynolds and running over 11 acres.

Ronnie Graham and Mick Wilkins were among the artists who contributed to the project, which was supported by Leader funding but financed largely by Beale. Wilkins set in stone the three faces of the saint after whom the garden is named, and Graham constructed the bog oak "throne" marked by granite pillars in the Bealtaine or "summer" garden.

The seasonal plantings, wildflower meadowland, nature trail and wind chamber built of local stone have attracted thousands of visitors since the garden was opened. Recent additions include a living willow play area, complete with tunnel, tepee and tent, and a deck from which to watch out for newts and dragonflies darting across the "lochan".

The completed sundial was a work in progress. There was no model to serve as a template, but Dr Brown came across a piece of software used by archaeologists and others known as Starry Night. "It tells you the position of all celestial objects at any time if you put in the latitude and longitude, and is used for checking alignments and that sort of thing." Whereas a normal sundial tells the time from the shadow's position as it moves clockwise around a curved dial marked with hours, the date can be ascertained from the shadow's length, he explains. In winter, the sun is low in the sky and the shadow is long, while it shortens as summer approaches and the sun is at its highest.

It sounds simple, but significant details have to be accounted for, such as the fact that the apparent motion of the sun in the sky varies. The positions of the shadow at different times of the day follow a convex or concave curve at different times of year - hence curved lines on the dial - the exception being the two equinoxes, marked by one straight line. As the rotating Earth revolves around the sun, the end of the rotation axis is tilted by 23.5 degrees. This tilt gives us our seasons north and south of the equator.

The Earth's orbit around the sun is slightly elliptical, which means that the speed is not constant. A sundial with a gnomon and straight lines on a horizontal face can be as much as seven minutes fast in late September and eight minutes slow in late March if this variable speed is not taken into account, Dr Brown notes. The final design accounts for the motions, with colour-coded times, dates, months linked by figure of eight curves or "petals" of successive "analemmas". The couple have prepared an explanatory leaflet, and plan to devise games around it for younger visitors.

Wilkins designed a compass, complete with Brigit's cross, for the dial, and the composite paving stones were sponsored by Origin Paving in Moycullen. Millimetre-sensitive construction was completed by Mick and Mícheál Lynch, known as the "two Micks". The couple won't forget early August last year, when a constant clear and sunny day gave them enough time to test it out over an eight-hour period. "We were like children, we kept running out, and it was very exciting," Beale says. "Even after all the work and effort and calculating, it was wonderful to discover that it was absolutely right."

Brigit's Garden at Pollagh, Roscahill, Co Galway, is open daily to Sept 30, 10am-5.30pm, cafe 11am-5pm. Adults: €6.75, concession: €5.75, children: €4 (under-fives free), family (two adults, three children): €20