a day. At the beginning of the summer the sun is at the point where the ecliptic strikes the northern tropic. The distance between the sun and the middle of the chart is then smallest (the sun has the greatest northern declination): consequently the sun then rises further from the centre, i.e. later and later, and also sets further from the centre, i.e. earlier and earlier. In midwinter the sun is at its greatest distance from the centre and rises after 8. am.: it then sets before 4. p.m.

That is roughly how this astronomical chart or Planisphaerium demonstrates the apparent rotation of the starry sky, with sunrise and sunset and the lengthening and shortening of the days.

Next, a straight vertical rod is seen to divide the circular opening

in the panel into two equal parts. This rod is the meridian. Its top (near the figure XII) is the southern point of the horizon: the northern point lies below.

From the middle of the meridian 6 curved lines of thin metal wire are drawn to the horizon. These lines, with the meridian, form the 8 cardinal points of the compass. The centre of the meridian, i.e. the point where the 6 lines meet, is the zenith or the summit of the firmament.

The straight lines, also of thin metal wire, drawn from the horizon to the astronomical pole (the centre of rotation of the astronomical chart) are hour lines. The sun rotates under these hour lines and thus indicates the time.

When photo 7 was taken, the sun had just passed the three o'clock line.

In addition, the moments of sun- rise and sunset are shown on two segments of a circle on both sides of the Planisphaerium, or chart.

On the longest day the sunrise pointer stands over the four, and that of sunset over the eight. The sun then rises before 4 am. and sets after 8 pm. After the longest day the days shorten, and from that moment both pointers start turning back. The sun now rises later in the morning and sets earlier in the evening: it rises after 8 am. and sets before 4 pm. again. After the shortest day, the days lengthen and both pointers return on their course.