In the summer of 2020, astronomy professor Donald Olson and colleagues in the physics department at Texas State University reported that Dutch artist Johannes Vermeer probably painted his famous ‘View of Delft’ (Figure 1) at 8am on 3 September 1659. Assuming that Vermeer accurately painted what he saw, Olson’s team reached their conclusion by mapping the buildings of Delft and studying the patterns of light and shade. They deduced the Sun’s position, and their software gave dates in April and September. The team felt that the trees in full leaf were more typical of an autumn date, though others argued that the boats would have been preparing for the summer fishing season.
Similar detective work — known as forensic astronomy — can be used to pinpoint the time and date of photographic evidence relating to crimes. The analysis exploits the fact that the Sun’s position in the sky depends on latitude, date and time of day. Figure 2 shows how the Sun’s path changes over 6 months at one location and Figure 3 shows successive images taken at the same time each day. The changing path and the figure-of-eight pattern (the solar analemma) result from the Earth’s axial tilt and its elliptical orbit. For a detailed explanation and animations, go to: www.tinyurl.com/solar-analemma
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