Having decided the location the next problem was to establish a very accurate north - south line for the alignment of the gnomon, by using the shadow of the sun. For this you need to know how many minutes your site is, in front or behind Greenwich, in solar time. Find the longitude of your site (e.g. using Google Earth or a Satnav). Our site is 1.27 degrees west of Greenwich. The sun moves across the sky at a rate of 15 degrees of longitude each hour, i.e. 1 degree every 4 minutes. 1.27 x 4 equals approximately 5 minutes behind Greenwich for our site at West Park, Long Eaton. You then need to consult the 'Equation of Time' graph or look up the daily variation on this page at "Sundials on the Internet". A nail was hammered into the end of a length of straight 50mm x 50mm timber (the taller the better in summer) & guy ropes tied to the nail. The pole was erected vertically & adjusted with great care using a spirit level. Record the position of the shadow with pegs ( 13.00 BST or 12.00 GMT adjusted for the previous two factors). Using a string extend this line well beyond the working area, using extra pegs, in case the original pegs are disturbed ( Video - Sundials and Latitude ).
( Graph of Earth's Tilt and Ellipical Orbit. Taken from: National Maritime Musuem - Shadows and Sundials ).
Our grateful thanks to AGA Rangemaster who made the gnomon at their Long Eaton factory free of charge. It was made from 100mm stainless steel tube & the internal angle between the gnomon & the horizontal brace was set accurately at 52.90 degrees, the latitude of our site. The picture below shows it assembled but awaiting the brushed finish.
Our installation engineer installed the concrete base using a template to position 4 pairs of threaded anchor rods.
The timber formwork was added to mould the plinth. At this stage the
gnomon was aligned accurately in 3 dimensions, along the north - south
line using the pegs & vertically using metal shims under the four
anchoring points. Our thanks to Pettits. The angle of the slope was set
by using a spririt level on the horizontal brace.
The positon of the gnomon was permanently set by concreting in the
plinth. Our thanks to Acton Timber yard & Arkwell Fasteners for
supplies.
After the plinth had matured a 6 metre circle was excavated around the
sundial. An edging of 12 lengths of tanalised timber was set in place.
The diagram below (sundial lines for the latitude of West Park, Long
Eaton) was transposed onto a larger piece of cardboard, on both sides.
Note that the cardboard is positioned correctly for a solid, triangular
gnomon. But our template was adjusted a little to the right such that
the marks lined up to the centre of the tube rather than the leading
edge.
( Sundial Line Calculator )
( Alternative Sundial Line Calculator ).
The lines on the cardboard were extended to the timber edging, adjusted
by 5 minutes (behind Greenwich), the hour markers put in place & the
aggregate consolidated. I strongly recommend that you wait for a sunny
period to check that you have the alignment correct using the 'Equation
of Time' graph or The British Sundial Society.
We had several sunless days and I misaligned the hour markers
initially! The concrete hour stones were cast in an inverted washing up
bowl with the base cut out. Our thanks to Wickes for the concrete
mixture. The mosaics set into the hour stones came from Mosaic Heaven at
Peterborough, the black mosaics are counted for GMT & the yellow
one added for BST.
Future development of the site will be a spiral planets path, centred
around the sundial, containing 9 circular beds of shrubs, of varying
sizes and colours to best represent the planets. Also a solstice stone
& equinox/solstice floral arches are being considered.
The shrub types have been specified by Long Eaton Horticultural
Society/Erewash in Bloom to best represent the colours of the planets.
Committed sponsors shown as at March 2011.
