Article of the month January

Babylonian and Italian hours. (2)

In Article of the month December 2004, Babylonian and Italian hours were described.
We will now describe some further properties.

We may draw lines through the intersections of the lines of both time systems, as in the figure above.
They are found to be straight lines, and are in fact hour lines for apparent solar time.

Only lines for the whole hours are drawn, so as not to crowd the figure, but half-hour lines could have been drawn directly as well.

The figure below shows another way of drawing lines through the intersections.
These are declination lines for days on which the sun is up an integer number of hours.

To the right is shown how many hours that is; left is shown how many hours remain for the night.

We refer again to the beautiful sundial on the gate of Prince’s Court in Groningen, which displays all this elaborately.