Nodal and meridian dials

The projection of a fixed point on the face of a nodal sundial can indicate the time of day as well as the date. The projection can be the shadow, but also a spot of sunlight formed by an aperture.
The ancient Romans already used obelisks as gnomon for their nodal dials, which they had brought as souvenirs from Egypt. The sundial of Emperor Augustus on the Campus Martius is well known. Recently I read that also the obelisk on the Place de la Concorde in Paris is being used for this purpose.

The moment of local noon is an important time point. The sun is right in the meridian, culminating at the same time. Meridian dials were used to read this moment. They can be considered a vertical dial, the face of which is reduced to hold only the noon line. Usually, a perforated disk was used as a gnomon.

Horizontal meridian dials were sometimes laid out in churches. The noon line was inserted into the floor, constituting a meridian line. The declination of the sun could also be indicated along the line. The passage of the spring equinox, for instance, provided the date for Easter.
The gnomon of a meridian line may produce very nice images during a solar eclipse.

The reflected ceiling dial is also a nodal dial. The dial face can be drawn on the ceiling (or other walls of a room). A small mirror fixed onto a south-facing window frame serves as the gnomon. Isaac Newton is said to have invented this type in 1660, when he made one in his grandma's house.
A famous, very elaborate dial can be seen in the Lycée Stendhal in Grenoble. It has been made by Father Bonfa in 1673.



Nodal dials - Netherlands
Transformer Company
Nijmegen
 Catholic University
Nijmegen
 "Zonnebol"
(Sun Globe)


Nodal dials - Europe
City Hall
Blois (France)
 Place de la Concorde
Paris (France)
 Reflecting dial
Lycée Stendhal
Grenoble (France)
(direct link)
 Reflecting dial
Reinhold Kriegler
Bremen (Germany)
(direct link)


Meridian dials
Monflanquin
(France)
 Notre Dame Church
Gray (France)



Meridian lines
Sundial Park
Genk (Belgium)
 Cathedral
Antwerp
(Belgium)
 Santa Maria degli Angeli
Rome (Italy)
(direct link)