Sundial calculation

A modern altitude sundial after Erasmus Habermel

A modern circular altitude sundial after Erasmus Habermel of Prague

Modern reconstruction of a 16th century altitude sundial for studying its mathematics and accuracy. An altitude dial uses the height of the sun to find the time. The dial is double-sided with the two half-years back-to-back.

Erasmus Habermel was a renowned scientific instrument maker working in the court of Emperor Rudolf II in Prague in the 16th century. He made instruments for all disciplines including astronomy and navigation. One of his sundials is an altitude dial in the clocks collection of the Augustine Museum in Freiburg im Bresgau*. It is an elegant circular dial and the mathematical construction is intriguing. Continue reading

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Calibrating a new obelisk sundial in stone

Inclined test dial facing east

This dial stone is a test piece for the new obelisk sundial, and is on a board at the correct angle for one of the faces of the obelisk. It faces East and inclines 61° to horizontal so the shadow of the temporary plastic gnomon will show the time.

Obelisk sundials carved in stone were popular in Scotland in the 17th and 18th centuries. Quite recently stonemasons in Fife have done the work to carve a new obelisk sundial for one of their clients. Its dials have remained blank for mathematical calibration. Macmillan Hunter are responsible for the calibration and have supplied detailed dial instructions and drawings for the mason to use together with the required set of geometric bronze gnomons. Continue reading

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North alignment on a Victorian pedestal

Sun direction measured with an angle finder

The direction of the sun measured against one edge of the octagonal stone pedestal using the angle finder and light slit

A Victorian sundial pedestal stands in the gardens of Riccarton estate outside Edinburgh. It once held a beautiful octagonal dial which is now in safe storage. A replacement dial is to go on show and it must be in a correct orientation. The gnomon on a sundial must point north. A wrong alignment will make the sundial inaccurate, and nothing on the 19th century pedestal actually marks the north. Continue reading

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Wall sundial at Royal Square in St Helier, Jersey

Wall sundial at St Helier, Jersey

Wall sundial in Royal Square at St Helier, Jersey, Latitude 49.1839° N, Longitude 2.1057° W. The inscription reads: REGULATE YOUR CLOCKS BY THE SUN DIAL. CORRECTION MUST BE MADE FOR THE EQUATION OF TIME WHICH IS GIVEN IN ALL THE ALMANACKS.

This beautiful sundial is set into the wall of the old Picket House in Royal Square, St Helier, Jersey. Historical records show it was made by a talented Jerseyman called Elias Le Gros in the 1820s. In spite of being plastered over at one time by the military authorities and then restored again in 1875 after a public outcry over the dial’s obliteration, it is now in excellent condition, as our photo shows. Our host for lunch that day told us: “The dial is much admired but of course it isn’t accurate.” Poor old Elias Le Gros, now was the time to rescue his reputation! Continue reading

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Restoration of a small brass garden sundial from the 1930s

Brass sundial from the 1930s restored with a new gnomonThis small brass garden sundial had lost its gnomon. It is dearly loved by its owner who has known it since childhood, and she wanted to have it restored. As often happens at different times the family moved home and the sundial moved too. Continue reading

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Rustic stone sundial in an Edinburgh garden

A stone sundial carved in rustic style for an Edinburgh garden

This sundial is delightful. It is the first piece of work by someone in Edinburgh who is learning to do stone carving. It is a very good sundial and they should be proud.

A sundial carved in stone is always special. This sundial is the first piece of work by a stone carver who has begun learning the craft of carving for their own pleasure. The result is very good. The rustic design suits the sunny spot on their slightly overgrown wall in the garden in Edinburgh so well.

Even a rustic design has to follow the sundial rules for the angles of lines on the dial and the angle of slope of the gnomon. Continue reading

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What is the declination of the wall for a sundial

The diagram illustrates a method for calculating wall declination.

Knowing the declination of the wall (WD) is important for designing a sundial. The basic calculation is azimuth angle (AA) minus protractor angle (PA) plus 90°. You can repeat your measurements for accuracy. Do ask for help if you are unsure.

“What is the declination of the wall for a sundial?” A stone sculptor asked us just this question recently . It is a good question because you must know the declination if you are making a sundial that is accurate for the wall. The sculptor was not confident about their own measurements and calculations so they asked us for help. Continue reading

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