Figure 4.

Three 180° field-of-view photographs (taken in Oulu, 65°0′ N, 25°26′ E) from the 15 pictures of twilight skies presented six times on a monitor to 18 test persons in the second psychophysical laboratory experiment. The task of the test persons was to guess the azimuth direction of the Sun below the sea horizon with the naked eye. The centre of the circular pictures points to the horizon, while the zenith and the nadir are the uppermost and lowermost points of the circle. The upper/lower halves of the pictures depict the sky/sea. The solar azimuth directions estimated by the test persons are shown by short vertical bars below the horizon. The long vertical bar above the horizon represents the average of these guessed azimuth directions, while their standard deviation is shown by the short vertical bars at the ends of the horizontal bar.