Gnomon

The gnomon is the triangular blade in this sundial. A gnomon ([ˈnoʊmɒn], from Greek γνώμων, gnōmōn, literally: "one that knows or examines") is the part of a sundial that casts a shadow. The term has come to be used for a variety of purposes in mathematics and other fields.

source:
en.wikipedia.org

image:
commons.wikimedia.org

Hour Line(s)

where L is the sundial's geographical latitude (and the angle the gnomon makes with the dial plate), is the angle between a given hour-line and the noon hour-line (which always points towards true North) on the plane, and t is the number of hours before or after noon.

source:
en.wikipedia.org

image:
mysundial.ca

Nodus

Media in category "Nodus-based sundials" The following 98 files are in this category, out of 98 total.

source:
commons.wikimedia.org

image:
sundials.ru