Time

A study of sundial calibration for eight selected altitude dials

Mathematical diagrams for the circular altitude dial.

This dial has circular graduations for dates. The gnomon is fixed, and the hour point on a circle is where the nodus shadow falls. A series of calculations for coordinates (X’, Y’) give the calibration for the whole dial. These calculations are by numerical iteration on computer.

Altitude dials are an intriguing type of sundial. There are many individual types, and they mainly date from around the 1600s or earlier. Our own design for a full-scale altitude sundial for the garden is a circular dial. It follows the same working principle as a circular brass dial in The Augustine Museum in Germany. We decided to investigate the calibration of eight different altitude dials, including the one from the museum, and we have now completed a study of their mathematics. We submit the report of our study in full for wider interest here: A Study of Altitude Sundial Calibration.

 

 

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A circular altitude sundial at full-scale for the garden

Altitude sundial in the garden

The altitude sundial in sunshine on 21st July 2026. The dial reads 3:50 pm, which is only 4 minutes difference from clock time, with corrections made for BST, Longitude, and EOT. The reading point is the tip of the shadow, which is the shadow of the gnomon nodus. 

The altitude sundial is an intriguing instrument. It relies on measuring the height of the sun to tell the time. It also requires the user to adjust for the time of year before making a reading. There are many altitude sundials and there is one particular one with a circular dial, from around the year 1600, which we find very interesting. We have now designed and built one like it at full-scale for the garden. Continue reading

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Inverkeithing Mercat Cross – sundial restoration complete

Inverkeithing Mercat Cross, the capital stone, cube sundial, and unicorn fully restored.

The Inverkeithing Mercat Cross is a tall stone column in the centre of the town. The capital stone, cube sundial, and unicorn sculpture are at the top of the column. There has been no ‘Cross’ as a Christian symbol on the column since the Reformation. Photo: Graciela Ainsworth.

The Inverkeithing Mercat Cross is a tall and handsome piece of historic town architecture. The Mercat Cross in Scottish towns was a symbol of licensed authority to trade in goods, and the trading place was at the Cross. The sundial would be a 17th century addition, now fully restored, together with the heraldic capital stone and the symbolic unicorn of Scotland.

The sundial is a cube stone which is ideal for a prominent place in a town. It is visible from all sides and it shows the time at all hours of the day. Continue reading

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Haddo House cube stone sundial restored and reading solar time

Haddo House stone cube sundial

This sundial cube stone has fine carving detail. Each of five faces can read the time. The horizontal dial carved in the stone on top indicates an ornamental piece for a garden. A cube set on a tall pillar or on a wall will have the side dials only. Photo: Graciela Ainsworth.

This cube stone sundial stands in the garden of Haddo House, the National Trust for Scotland property in Aberdeenshire. When we examined it at the workshop, it had broken and missing gnomons and moss obscured the dials. After restoration the dials can now read solar time properly again.

A cube dial has the mathematical attraction of reading time by the sun on south, east, west, and north faces. As a result, as the sun moves round, the cube sundial is an excellent device for showing time Continue reading

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Butterton church sundial and memorial brass from Tideswell

Butterton Church sundial restored

The Butterton church sundial has a new brass gnomon on the old dial plate. After many years outdoors the brass plate has turned green in colour. The Gothic script on the back of the plate shows it came from the Pursglove memorial in Tideswell church.

A few years ago we restored the sundial at St Bartholomew’s Church in the lovely Staffordshire village of Butterton. We found that the brass dial plate had ancient engraving in Gothic script on the underside, which was a mystery. The writing looked like part of a memorial brass, and we now know it came from Tideswell church in Derbyshire. Continue reading

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Sundial stones in a Scottish garden — the restoration

Ancient sundial pillar after restoration

A falling tree broke off the top of this pillar in Storm Arwen. The two sundial stones fell down to the ground. The pillar now has a new top section matched to the original stone. The sundial sections are clean and restored.

In November 2021, Storm Arwen caused serious damage with very strong winds especially in eastern Scotland. On one country estate an oak tree crashed onto this historic sundial in the family garden. It smashed the ancient pillar supporting the sundial stones. The family wanted to see the sundial fully restored. Continue reading

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Sundial stones found in a Scottish garden — the cruciform stone

Cruciform sundial stone

The cruciform stone has four concave sides leaving four curving arms between them, thus creating the cross shape. This particular stone has a small concave end on each curving arm [not visible in the photo]. So the single stone has eight dials, on four large concave sides and four small ones. [Note: the shadow in this photo is from indoor lighting not from the sun.]

The cruciform type of sundial stone is a clever idea. During the day, as the sun moves round, each of the dials in turn will show a shadow and indicate the time. The straight dial edges cast the shadows. A cruciform stone can be on a lectern sundial but this one appears unique. Continue reading

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Sundial stones discovered in a Scottish garden — the stone globe

Globe terminator stone sundial

The globe sundial will show light and dark sides of the stone in sunshine. The terminator line separates the two and the hour numbers show the time.

This stone globe was initially puzzling. It has a band of hour numerals and looks like a type of sundial. It is actually a globe terminator dial. The hour band lies parallel to earth’s equator, and the line between light and dark shadow in sunshine is the terminator. The puzzle was why the globe had a second sundial  stone fixed onto it, since removed in the workshop, as a later post will explain. Continue reading

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A design of azimuth sundial to go in a garden

Azimuth sundial on 10 October at 11.10am

On 10 October the autumn equinox has passed and the cursor reading point has moved out from the inner circle of the dial towards winter solstice at the circumference. The sighting arm carries a short vertical gnomon which casts its shadow in line with the sun.

The azimuth sundial is an intriguing instrument. It finds the time from the direction of the sun. This idea sounds simple, the sun rises in the East, at Noon it is due South, and it sets again in the West, but it is complicated by the time of year. This note is about a new design for a precision azimuth sundial to go in a garden. Continue reading

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Armillary sundial on the day of autumn equinox at noon

Armillary sundial on the day of the autumn equinox at noon

Every day at noon the gnomon rod casts its shadow on the centre line of the meridian band. When the day of spring or autumn equinox arrives the two orb balls cast a double shadow onto the meridian band. Away from the equinox, only one orb shadow will show.

Our armillary sundial casts distinctive shadows at noon on the day of autumn equinox, as seen in the photo. Its unique design allows the noon shadow of the gnomon rod to fall on the broad meridian band at its centre line. The two orb balls also cast their noon shadow onto the meridian band. Continue reading

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