Equatorial dials
The most frequent sundial type in the Netherlands is the armillary sphere. The time scale has been applied to a ring in the equatorial plane, perpendicular to the pole-style. Often, several more rings are present, to support the pole-style and the hour ring, or to model the tropics, arctic circles or horizon. This multitude of rings may block the shadow of the pole-style on the hour scale, or at least cause confusion when reading the dial.
The sun proceeds 15° per hour, which is also the angular distance of an hour on the time scale. The scale thus is linear (or homogeneous), which implies that it could simply be moved by an hour to accommodate daylight saving time, for instance.
Most armillary spheres are not my taste, but I do like the specimens below, because of their setting, or their shape or color. Especially the 'reduced' dials, stripped of all unnecessary material, are elegant.
One may exchange the positions of the pole-style and the hour band, and read the dial by using a perforated hour band. At the bottom are examples of such an 'inverted' armillary sphere.
There is another type of pole-style dial that is also called equatorial. Actually, that is the original equatorial type. It has a disk-shaped dial face, pierced by the pole-style. The hour lines run radially from the intersection point, at intervals of 15°, on both sides of the dial face. The top face is used in spring and summer, the bottom face (if present) in autumn and winter.
I call this original type the equatorial disk dial. The table below starts listing the few dials of this type in my collection. In most sundial books, the armillary sphere is presented as a derivative of this type of dial. The dial face is considered to be reduced to the annular edge of the original disk-shaped face. I see more of a correspondence between the armillary sphere and the horizontal and vertical dial, than to the latter type.
Equatorial disk dials | |||
Headquarters NAM, Assen |
Schreyers Hoek Emden (Germany) |
Sundial park Jaipur (India) |
Armillary spheres - Rest of the World | |||
Henry Moore Adler Planetarium Chicago (USA) |
Sundial Park Jaipur (India) |
Technical University (Hong Kong) |
'Inverted' armillary spheres | |||
Whitehall "Sunclock" Our former garden Peize |
Am Angelser Feld Bremen (Germany) (direct link) |
Wehlen (Germany) |
Nature's Garden Park, Branford (Conn., USA) |