Longest photo exposure of all time

In 2012, photographer Regina Valkenborgh, then a student at the University of Hertfordshire in England, created a series of makeshift pinhole cameras by lining drink cans with photographic paper. She forgot about some of them and one remained in place for 8 years before someone found it. It contained what might be the longest photo exposure in history

The image shows the 2,953 arced trails of the sun as it rose and set through nearly a decade of changing seasons. … [It] shows the evolution of the Bayfordbury Observatory — the dome of the observatory's oldest telescope is visible to the left of the image, while the atmospheric gantry, which was built halfway through the exposure, can be spotted from the center to the right of the picture.

From the university's press release:

"It was a stroke of luck that the picture was left untouched, to be saved by David after all these years. I had tried this technique a couple of times at the Observatory before, but the photographs were often ruined by moisture and the photographic paper curled up. I hadn't intended to capture an exposure for this length of time and to my surprise, it had survived. It could be one of, if not the, longest exposures in existence."