Article of the month November

Hāfir

In the book 'Gnomonik der Araber' of Karl Schoy, 1923, we find a description of certain horizontal sundials where the time is read using the length of the shadow of a vertical gnomon. Such a sundial is called a Hāfir.

Schoy refers to literature from which it appears that such sundials were known from the middle ages. The time is therefore read in antique (unequal) hours.
For antique hours, see also Article of the month July 2005.

Islamic prayer lines appear on these sundials as well.
For these lines, see also Article of the month August 2004.

Antique hours

Because of the vertical gnomon, the sundial is date dependant. This explains the presence of a date scale, divided according to the signs of the zodiac.
This date scale consists of lines that are 30 degrees apart.
Of course the date scale could be subdivided further, but for the sake of clarity that was not done here.

In order not to overload the figure, the Islamic prayer lines for this sundial are drawn in a separate figure.

Islamic prayer times
From the inside out:
Zuhr
Asr-i evvel
Asr-i sāni

In use, the sundial is placed horizontally and turned so that the shadow of the gnomon falls along the line for the current date.
Time is then read on the terminus of that shadow.