My suggestion for a playground sundial would be -
Mount a small mirror (silvered metal, not glass) on a vertical wall, ideally
south-facing. It should be out of reach for children, but accessible to a tall
adult. The mirror could serve as the nodus for a horizontal sundial marked on
the ground. The reflection of the sun would be a patch of light, telling the
solar time.
The network of hour-lines and declination lines on the ground would in fact be
a map of the geographical latitude and longitude of the location at which the
sun is instantaneously overhead, in gnomonic projection. Oceans and continents
could be mapped on this network. Places in the news (Benghazi, Afghanistan)
could be chalked in. Significant dates (school holidays, even Ofsted
inspections) could be traced as declination lines.
Loads of educational spin-off -
Geography - Map projections; latitude and longitude; points of the compass.
Physics - Optics of the mirror.
Religious instruction - Date (declination line) for festivals of different
faiths; direction of Mecca and Jerusalem.
Maths - Distance of e.g. Rome = radius of the earth x arctan(height of mirror /
horizontal distance of Rome on playground map); conic sections (why are
the declination lines hyperbolas?)
Astronomy - Zodiac signs linked to stellar constellations.
Each child could take home a miniature version on folded card, with the mirror
replaced by an aperture. Declination lines could then mark birthdays of
parents, siblings and pets.
This surely beats the anallematic sundial, and still leaves a margin for my
consultancy fee.
John Lynes
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