Time measurement

Function of the scaphe - how to read the time on the scale

As the sun moves from east to west in the course of a day, the shadow of the gnomon moves from the left to the right, i.e. from west to east.

The shadow of the gnomon tip moves from hour line to hour line.
It tells the temporal hour.

with the sundial Skaphe the winter solstice can be precisely determined ©Björn Oldsen

View at the winter solstice

with the sundial Skaphe the equinox can be exactly determined.  ©Björn Oldsen

View at the equinox

with the sundial Skaphe the summer solstice can be exactly determined. ©Björn Oldsen

View at the summer solstice

At the winter solstice, the shadow is the longest and the shadow point of the gnomon tip runs along the top-most horizontal line. At the equinox in spring and autumn, the shadow moves along the middle line. At the time of the summer solstice, when the shadow is the shortest, the shadow point can be observed along the bottom-most line.

Replica of a sundial as it was built approx. 2000 years ago

What are "temporal hours?"

From the time of classical Greek Antiquity to the beginning of the spread of mechanical clocks in the modern era, the "light day" from sunrise to sunset used to be divided into 12 equal hour sections.

Temporal hour 1 begins at sunrise. Hour 7 corresponds to the zenith of the sun, i.e. midday. Temporal hour 12 is at sunset.

The length of hours varies based on the changing duration of sunshine in the course of the seasons. This way, people's working lives could be optimally adjusted to the brightness of the day. "Working times" were longer in summer than in winter.

This vertical dial shows the temporal (black) and equinoctial (red) day hours at the same time.

Temporal hours as compared to equinoctial hours by the example of the duration of sunshine in Frankfurt a. M. (Germany)

The temporal hour is twice as long in summer as it is in winter. The 12th hour would begin before 4 pm according to our current measurement of time in winter.

External link about sunrise, sunset and daylengths:


For how long does the sun shine in our region?

The daily duration of sunshine depends on the orbit of the Earth around the sun. The northern hemisphere is slanted towards the sun for half a year due to the inclination of the Earth. Therefore, the sun shines for a rather long period in summer. The other half of the year, however, that hemisphere is inclined away from the sun. Therefore, the duration of sunshine in winter is rather short.

Inclination of the earth axis

The rotational axis of the Earth is called the earth axis. It runs through the south and north poles. At the same time, our Earth circles around the sun once in a year. The orbit level is called ecliptic. The earth axis is not at a right angle to the ecliptic, but inclined by about 23.4°. This inclination is also called the declination.

Since the inclination of the earth axis is always preserved, the angular distance δ changes from +23.4° on the day of the summer solstice to -23.4° on the day of the winter solstice. The sun stands vertically above the northern tropic on 21 June and above the southern tropic on 21/22 December. In the time between these dates, it will, therefore, pass vertically above all latitudes in between twice.

In addition to this, the sun does not rise above the horizon at the northern-most latitudes in winter, and does not set there in summer (midnight sun).

Since the length of shadows depends on the latitude and the seasons, the scale of the scaphe will be adjusted to your location to the degree. Therefore, enter the latitude of your location in the contact form. You can determine the matching latitude here (no decimal digits).

The sundial needs a sunny place

Setup and alignment of the scaphe

Align the sundial with the scale pointing north. It is best to use a compass for this. Now ensure that the scaphe is placed perfectly horizontally.