Article of the month June

Altitude dial 1

Shepherds’ dial

A common type of sundial, which tells time from the altitude of the sun, is the shepherds’ dial.
It is generally a vertical cylinder, the surface of which is divided into a date scale, using the signs of the zodiac, or calendar months, or even both.

On top is a rotating horizontal indicator pin, which is turned over the actual date.
The sundial is held upright and turned until the shadow of the indicator falls vertically down the date scale.
The hour lines then indicate the time, provided you know if it is before or after noon.

Both examples show divisions using both zodiacal signs and calendar months.
On the smaller sundial the zodiac is continued around the cylinder, on the larger the monthly.

One sundial reads almost 10 o’clock, the other almost 11.
This is because the second reads summer time (DST).

These sundials can be classified as pocket dials or as portable dials.
Often, the indicator pin is stored inside the cylinder when not in use, as shown below.

There are larger ones, like this modern, fixed specimen in Japan. It is about 2.5 meters tall.
The rotating indicator is aimed at the sun, and then the rotating cylinder surface with the vertical date lines is turned so that the current date is below the indicator.