Oughtred's Double Dial

The double dial shown here with its sun's altitude scale and detail of the astrolabe portion. Both the inclined sundial gnomon and the vertical astrolabe gnomon can be seen plus the calibrated rotating rule which finds the time on the astrolabe and indicates the other functions of the dial as listed below.

The Double Dial is part sundial and part astrolabe. It was developed during the early 1600's by
William Oughtred of London, a noted mathematician of his time. 

In its horizontal form the dial will tell:-
Local Solar Time, South African Standard Time, time of Sunrise and Sunset, Azimuth of the sun from sunrise to sunset, Declination of the sun, sun's Altitude, Day, Date, Month, Season, Solstices and Equinoxes.
This for each and every day of the year.
In addition it is a solar compass because when time on the horizontal dial and time on the astrolabe
correspond, the instrument is orientated perfectly to the meridian or true north/south.
The sundial will also read time during lunations.
The Equation of Time and the Longitude Correction must be applied to all readings to obtain the legal hour.

The example above is highly unique in that it was made for the southern hemisphere and stands
within the Tropic of Capricorn in central Namibia.
There is no known record that shows such a dial having been made before.
It is of solid stainless steel and 390mm across flats. The astrolabe portion being 288mm in diameter.

All Double Dials are site specific and a separate instrument is needed for each location.
Both Northern and Southern Hemisphere formats are offered in brass or stainless steel.
Inscriptions, family crests etc can be added along with global position and date.

The altitude scale contains an explanation of the instrument's usage and is mostly used after the sun's
apparent transit of the latitude between December and January each year.

Contact us

Click a link below to go to:-
Triple Dial, Armillary Sun-Moondial, Horizontal Sundials, Armillary Spheres,
Noon Cannons, Antarctica Sundial, Favourites,
Moondial, Horizontal Projection Instrument or Astrolabe,