What happens when a drinks can photographs the Sun for six months?

A photograph of the Sun may bring a round disk to mind. In the solargraph presented by NASA, there are curves instead: many paths recorded by a small stationary camera between the winter and summer solstices, overlaid in the same patch of sky.

The camera in that example was an aluminum can containing photographic paper. Light entering through a small hole left traces as the Sun moved across the sky. A clear day could produce a relatively continuous path; clouds could interrupt it. Because the Sun’s height changes with the seasons, each day’s line falls in a different place.

Light passing through the pinhole reaches different parts of the paper according to its incoming direction. If the paper stays in place and the can does not move, light arriving from a similar direction the next day leaves a trace in a similar position. Keeping the camera fixed matters more here than pressing a shutter.

The Sun appears to cross from east to west during a day, while the height of its path changes through the year. Months of observations from one location produce layered tracks, some interrupted and others long. A short line does not mean the Sun moved less that day: clouds or obstructions may simply have reduced the light reaching the paper.

The lead image is a separate example from Cerro Paranal in Chile, published by the European Southern Observatory. Solargraphs from different locations show different buildings and terrain, yet share the bands formed by repeated solar paths recorded from a fixed position.

Everyday photography often uses a short exposure to avoid blur. In this image, the long wait is part of what is being recorded. Small differences in the sky seen each morning become stripes when months are brought together on a single sheet.