Information About Sundials

HORIZONTAL DIALS

Unless specially made for a specific latitude, our horizontal dials are set for the average latitude of the British Isles and Northern Europe. Setting up a sundial in the garden could scarcely be easier: ensure that the base is horizontal and in a place where it will receive full sun. At 12 noon Greenwich Mean Time on a sunny day, position the plate so that the shadow of the gnomon corresponds with the 12 (or XII) mark on the dial.

If you look at the Equation of Time graph, you will see that sundial time corresponds with clock time most closely on four occasions during the year. These dates are April 15, June 15, September 2, and December 24, so if you have choice, choose a day as near as possible to one of these. In the Northern Hemisphere the gnomon or pointer rises towards the north (and towards 12 o’clock). To be accurate it should point at the North Star, Polaris.

The earliest astronomers in classical times created their own concept of the Celestial Sphere, visualizing the Earth surrounded by projected bands of Colures, reflecting the Solar System as they saw it. Angled to correspond with the fixed point of the North Star, the Sphere indicated the apparent course of the Sun – the Path of the Ecliptic – around the central orb of the Earth itself, the Equator, the Tropics, the Meridian of the Solstice and the intersecting Meridian of the Equinox.

The first Queen Elizabeth was probably familiar with this illustration of a full armillary Sphere which featured in a book published during her reign in the 16th century. By then it was realized that, with a time scale added to the Equatorial band they made reliably accurate sundials, and this became their chief use. As ornamental garden features they attract the eye, form a natural talking point, and seem to emanate a quality of ancient erudition.

If your armillary includes the Band of the Ecliptic and a central orb, this can be seen as a self-contained three-dimensional model of the Celestial Sphere, with the apparent path of the Sun as it seems to encircle the Earth. looked at another way, the circle of the Ecliptic indicates the plane of the Earth’s orbit around the Sun against a background of stars, in particular the constellations of the Zodiac. The two intersections of the Ecliptic with the Celestial Equator indicate respectively the first point of Aries, marking the advent of Spring in the Northern Hemisphere, and the first point of Libra, marking the commence- ment of Autumn.

At the intersection of the Ecliptic with the Northern Tropic of Cancer the Sun is overhead on the 21st June, and at its intersection with the Southern Tropic of Capricorn the sun is overhead on the 22nd December.

June 21st:

Summer in the Northern Hemisphere, with the North Pole in daylight.

Winter in the Southern Hemisphere, with the South Pole in darkness.

December 22nd:

Winter in the Northern Hemisphere, with the North Pole in darkness.

Summer in the Southern Hemisphere, with the South Pole in daylight.

A TRADITIONAL MOTTO