The Sun's paths in the sky

We are so used to the Sun's presence in the sky that we no longer pay attention to its changes throughout the year. We know that the days are shorter in winter and vice versa longer in summer. But many still think that the different temperatures of the seasons depend on the distance of the Earth from the Sun. In fact, this is only a small effect and what actually matters the most is the height of the Sun above the horizon: lower in winter, higher in summer.

Franziska Zeuner, a postdoctoral fellow at the USI-affiliated Aldo e Cele Daccò Solar Research Institute (IRSOL) in Locarno, used a simple pinhole camera to follow the Sun's path over six months, obtaining a striking image in which the lowest bright streak corresponds to the winter solstice. The stripes in the solar paths show the alternation between sunny and cloudy days.

The simplicity of the instrument used is incomparable with the high technology of the Institute's equipment, which instead observes the Sun in detail to study its magnetic field and the surface phenomena of our star. Phenomena that, if they reach extreme energy levels, can also have consequences for our technology and civilisation. While on a larger scale the Sun has always, moving across the sky along elegant and regular paths, marked the passage of days and seasons.