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Galway Sundial

This 16 metre diameter calendar-sundial has fifteen declination lines, one for the first day of each month, one for the equinoxes and two for the solstices. The shadow is cast by a 1.75 metre high bog oak gnomon with the tip of the shadow indicating the time and date.

The instructions to tell the visitor how to read the dial are quoted in green text below:-

If it is AFTER 21st June this notice explains how to read the sundial.
If it is BEFORE 21st June please read notice on OTHER side of the sundial.

A normal sundial tells the TIME from the position of the shadow on a curved dial marked with the hours. The Calendar Sundial also tells the DATE from the length of the shadow. In the winter the sun is low in the sky and the shadow is long. In summer, the sun is high in the sky and the shadow is short.

The bog oak spike is the GNOMON that casts the shadow.
Step 1: estimate the date
Around the edge of the sundial, you will see the months marked in GREEN. The green curves show where the shadow falls on the first day of each month. If the end of the shadow falls between two green curves, you can estimate the date. (You need to IGNORE the YELLOW lines as they apply to the first half of the year)

Step 2: estimate the time
The Sun moves across the sky during the day so the shadow moves across the sundial. On the first day of each month, the time can be read from the hour marks. On other dates, you can estimate the time between the green lines connecting the hour marks. (Again, try and ignore the YELLOW lines)
The straight blue line shows how the shadow moves on the spring and autumn equinoxes (March 21st/22nd and September 21st/22nd). The blue line closest to the gnomon shows the end of the shadow on the summer solstice (June 21st), the longest day of the year. The blue line furthest from the gnomon shows the end of the shadow on the winter solstice (December 21st), the shortest day of the year.

The Analemma
If you look at the lines joining the hour marks you will see long petal-shaped curves. If the Earth's orbit round the Sun was exactly circular these lines would be straight. But the Earth's orbit is slightly oval-shaped, causing the variation in the position of the sun in the sky that produces the curves. This effect is known as the analemma.
On the Greenwich meridian in London the sun is at its highest point in the sky at 12 noon GMT. Because we are about 9 degrees west of Greenwich the sun is at its highest at about 12.35 pm GMT or about 1.35 pm during Summer Time. At this time the shadow points due North on the sundial.

The design and construction team included Jenny Beale, founder of Brigit’s Garden, her husband Dr Colin Brown of NUI Galway was the designer, Máire Ní Chíonna the site engineer, Mick Wilkins stone carver, Ronnie Graham was resposible for the bog oak gnomon, and Mick Lynch and Micheál Lynch laid the stone.

Brigit's Garden is open to the public during the summer and is just a 20 minute drive north of Galway city, 2km from the N59 between Moycullen and Oughterard. It is well signposted from the main road.

Lat 53° 23' North    Long 9° 15' West

Irish Grid    M  117000   238000

        Many thanks to Jenny and Colin for information and photos of their dial. Visit their website

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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