In astronomy, an analemma is a diagram showing the position of the Sun in the sky, as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble the figure 8.
The north–south component of the analemma results from the change in the Sun's declination due to the tilt of Earth's axis of rotation. The east–west component results from the nonuniform rate of change of the Sun's right ascension, governed by combined effects of Earth's axial tilt and orbital eccentricity.
One can photograph an analemma by keeping a camera at a fixed location and orientation and taking multiple exposures throughout the year, always at the same time of day. For this project, approximately 1,200 images are recorded every day, which will be used to reconstruct analemmata between 09:45 and 13:15 UTC. Pictures are recorded every 10 seconds. Accurate timing is provided by a daily synchronisation with a local time server. The system is UPS power-assisted and keeps time through a hardware clock. This project utilizes a Raspberry Pi Camera Module v2. The 2464 × 3280 pixel Sony IMX219 chip covers 48.8 × 62.2 degrees on the sky and allows for recording pictures between approximately solar azimut of 165 and 215 degrees.
The graphic below shows the 11:00 UTC analemma for Stockholm. The individual dots represent the current
coverage of the analemma project: grey dots = system inactive, dark dots = pictures taken, but day clouded out, orange dots = pictures taken, clear skies
To inspect the daily housekeeping data, follow this link. The probably most interesting plot, showing the solar visibility for today, is here (time given in local time, respecting daylight saving time):
Further control plots (System stats) show the CPU and memory usage of the system.