Glossary of sundial words
The glossary explains sundial words. Some words are unique to sundials. Some are everyday words that mean something particular for sundials. The glossary will help in understanding the principles of sundials and time, which have a long history. The selected list of further reading provides background and will lead to more precise definitions than are given here.
ANALEMMA. A continuous line on a dial that marks mean time at a particular hour, eg 11 o’clock. It is the equation of time applied to solar time. It applies the whole year. Its shape is a twisted loop like a figure-of-eight.
AUTUMN. The season that starts at the September equinox (March in the southern hemisphere).
CLOCK. An indicator of mean time.
EQUATION OF TIME. The difference between mean time and solar time. It is normally printed as a table that gives the number of minutes (plus, minus, or zero) that apply on each day of the year.
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GNOMON. The pointer on a sundial.
GREENWICH MEAN TIME (GMT). The mean time used in the time zone centred on Greenwich, UK. GMT is the national time for the UK.
HOUR. The equal time period in a 24 hour day.
LONGITUDE CORRECTION. The difference between time at the meridian of the time zone and time at the local meridian.
MERIDIAN. The local line of longitude.
NODUS. A measurement point fixed on the gnomon.
ORBIT. The circuit of a planet round the sun.
POLAR AXIS. The line that runs through the south pole and north pole. The earth rotates on its polar axis.
SPRING. The season that starts at the March equinox (September in the southern hemisphere).
SUMMER. The season that starts at the summer solstice.
WINTER. The season that starts at the winter solstice.
The reading list is brief. It is a starting point on the subject, before considering the vast literature that exists.
The British Sundial Society. The society’s website is a comprehensive resource on sundials. The society’s membership, activities, and publications are pre-eminent worldwide.
Sundials: history, art, people, science. by Mark Lennox-Boyd. Frances Lincoln, 2005. This beautiful book tells the whole fascinating story of sundials in a most enlightening way. Sir Mark Lennox-Boyd is Patron of the British Sundial Society.
Sundials. by Christopher Daniel. Osprey Publishing, 2004. This little book is an eye-opening introduction to amazing sundials, past and present. Christopher Daniel MBE is President of the British Sundial Society.
Greenwich Time and the Longitude: Official Millennium Edition. by Derek Howse. Philip Wilson Publishers, 1997. This book tells the complete story of time measurement. Derek Howse was Head of Navigation and Astronomy at the National Maritime Museum, Greenwich.
Shadows Pro. This all-embracing website carries an astonishing depth of information on sundials, astrolabes, and astronomy. Every type of instrument is covered, including workings, construction and photos, plus calculation software.
The Ancient Sundials of Scotland. by Dennis Cowan. Blurb.com, 2011. This book is a showpiece for the very best of Dennis Cowan’s wonderful photographs of Scottish sundials. The sundials are old and very beautiful taken in their historic surroundings.