NOON DIALS

A noon dial / noon mark serves as a method of pinpointing midday, when the sun is at its highest and due south. The origins are ancient. Here, the relevant area is in the centre, flanked by Roman numerals. My maths / science skills are few and I will spare you a rudimentary explanation. The key words are Equation of Time, Analemma, and (my non-technical choice) figure of eight.

In the centre of the dial is a narrow figure of eight bounded by the numerals. You can just make out the raised bracket that supports a slender gnomon. You can see a small ring through which, at the perfect moment, the sun’s rays strike the face of the dial:

If you want to know more, there is a concise entry at ANALEMMA (Wiki)

GREEN TEMPLETON COLLEGE OXFORD

A modern (1995) noon-dial commemorating the Bicentenary of the Radcliffe Observatory, designed by the renowned Christopher Daniel, founder of the British Sundial Society. The critical alignment of the sun’s rays are projected onto the surface of the dial at noon (MERIDIES MEDIA), focused by the small ring.

THE COLLEGE’S NOTES

• It works by using a spot of light cast by the nodus (the gilded sun with a hole in the middle), falling upon the slate dial-plate and tracking from left to right across it.
• It is declining because the wall it is attached to does not face due south but ‘declines’ away from the compass point
• Noon-mark means it gives the point at which the sun at its zenith crosses the Greenwich meridian and the Oxford meridian (the vertical white line down the centre of the dial)
• Mean-time means you can read clock-time from the dial by following the progress of the year along the figure-of-eight marking, known as an analemma or equation of time correction curve. This makes allowances for the effect of variations in the apparent motion of the sun at different times of year.

GSS Category: Analemma; Equation of Time; Munich Sundial; Nodus; University Sundial

CREDIT: John Renner, for another great find from his travels