Nocturnal of Nachtwijzer, Ca. 1640
Anoniem, UK
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Deze palmhouten nachtwijzer of ‘Nocturnal’ laat toe om aan de hand van de Poolster en twee extra sterren van de Grote of Kleine Beer (‘pointers of'Both Bears') het uur af te lezen. Daarnaast kan men op de achterzijde, die getoond wordt, de correctie aflezen die nodig is om met de Poolster de ‘latitude’ juist te kunnen berekenen.
This 17th-century boxwood English nocturnal has pointers for both the Great and the Little Bear constellations. Some nocturnals had pointers only for one of the bears.
A nocturnal is a device for telling the time by the stars. It could be accurate to about 15 minutes. They were popular from around the 15th to the 17th century, with a few being made into the 18th century.
How to use a English boxwood nocturnal:
• Set the long pointer to the correct date (the outer scale)
• Hold the instrument by the handle at arms length.
• Look through the hole at the centre at the Pole Star
• Once in position, move the two short pointers labelled 'LB' for Little Bear and 'GB' from Great Bear until they are lined up with their appropriate constellations.
• As the pointers LB and GL move, so does the time scale.
• Where this scale crosses the long pointer read off the time On the backside one can find the regiment of the polestar, as in this period the polstar had a distance of 2,6° from the North Celestrial pole