Article of the month December
Babylonian and Italian hours (1)
We are used to a time system that divides a full day into 24 hours.
We count from zero up to 24 hours, or in two periods of 12 hours each, but noon is always 12.00 hours.
That is not always true noon, in the middle of the day. For that, we must count in solar time..
In the course of history, other time systems have been in use.
We will mention two systems that are also based on a full day of 24 hours, and which count from 0 up to 24 hours.
It is only the starting points of these counts that are entirely different from what we are used to.
These systems are:
Babylonian hours
Italian hours
A point (or nodus) dial can indicate these hours.
Babylonian hours start with sunrise at 0 hours.
Because the duration of daylight changes in the course of the seasons, it takes longer in summer for it to become noon than it does in winter.
That means that the time of true noon is variable.
In our country, on a latitude of approximately 52 degrees, the times of true noon at the beginning of the seasons are:
| At start of season: | time of true noon is: |
| Spring | 6:00 Babylonian |
| Summer | 8:15 Babylonian |
| Autumn | 6:00 Babylonian |
| Winter | 3:45 Babylonian |
The time of day, expressed in Babylonian hours, indicates directly how many hours the sun has shone that day.
Horizontal sundial with Babylonian hours.
Italian hours start with sunset at 0 hours.
Again, the time of true noon is variable. Note also that the duration of the night is included in the hour.
In our country, on a latitude of approximately 52 degrees, the times of true noon at the beginning of the seasons are:
| At start of season: | time of true noon is: |
| Spring | 18:00 Italian |
| Summer | 15:45 Italian |
| Autumn | 18:00 Italian |
| Winter | 20:15 Italian |
The time of day, expressed in Italian hours and subtracted from twenty-four, indicates directly how many hours the sun has yet to shine that day.
Horizontal sundial with Italian hours
By drawing both systems on a sundial and adding colour, a beautiful mosaic results.
The two time systems combined
Both time systems are shown on the splendid vertical sundial on the Prince's Court gate in Groningen.
See also Sundial of the Month, 2003 archive, month 03-03.