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Astronomy through a pinhole

You can make some astounding images using just a box with a hole. Inspired by the celebration of Leiden as the European City of Science, Professor Matthew Kenworthy left several pinhole cameras across the Observatory over the course of 2021. This is how the simplest devices may uncover the greatest patterns.

Matthew Kenworthy has always been fascinated by the so-called pinhole camera: cameras that don’t need a lens and use just a hole in the side of a dark box. As a child, he got a pinhole photography kit. ‘You had to put the photosensitive paper and chemicals together, which was amazing. But also could easily go very wrong.’ 

Fast forward to 2021, the now associate professor at Leiden Observatory realised that in 2022 Leiden would be the European City of Science, and pinhole images could be his personal link to the celebration. When Kenworthy found out about SolarCan, a British pinhole camera manufacturer, he had an idea: to spread the soda can-looking cameras around the old Leiden Observatory to see what he would get. 

Two out of five survived

Between the summer and winter solstices – 21 June and 21 December 2021 – Kenworthy and Remko Stuik, another researcher at the Observatory, left five cans in different places around the observatory. By December, two of the cans had filled with rain and another was snatched. Luckily enough, two made it to the end of the year. They revealed beautiful ribbon-like smears of white light behind the Old Observatory telescope domes. “Each trace in this series of hoops and ridges represent the Sun travelling across the sky from sunrise to sunset every day,’ says Kenworthy. 

Each ribbon shows the path of the sun on a particular day

‘If you could sit back in your garden and keep your eyes fixed for six months and add up all those images, that's what you'd see: different effects and different astronomical phenomena happening. The Sun never traces out the exact same line in the sky,’ Kenworthy says. 

Stepping away from our timescale

It’s beautiful how simple pinholes can teach us about some of the most fundamental workings of our planet and Universe. ’Recording the paths of the Sun over a few months teaches us the Earth has a tilt, it has seasons, and that the Earth’s orbit is very, very slightly elliptical – which means that we get slightly closer to the Sun in early January than at any other time of the year,’ the professor explains. Additionally, long experiments like these are a great way to step away from the busy human timescale.

Simple fundamentals make for easy engagement

Kenworthy considers projects like this to have great educational potential, besides being pieces of art. ‘If you took a picture of the sun, every day precisely at midday and added all those images together, you'd see that the sun would trace out a lopsided figure eight in the sky. This shape, called an analemma, is dramatically different for the other planets in our Solar system. Some are either teardrop shaped, or a stretched out figure of eight, or a simple ellipse, for example,’ he says. 

'These images connect our daily human experience with the changes in the sky over the course of the celebrations this year.'

Working with pinhole cameras, sundials or solar photography could engage children in schools in learning about the stars and the motion in the sky – a move Kenworthy hopes can be possible after the pandemic eases out. ‘Anybody older than six can do it. You could involve them in a social media project to show their results and engage them with recording the Sun’s analemma by themselves, for example.  Because the fundamentals are so simple there are countless possibilities for engagement’, Kenworthy concludes. 

European City of Science

One idea is to have the images exposed in one of the several events at place in Leiden during its celebrations as the European City of Science in 2022.’These images connect our daily human experience with the changes in the sky over the course of the celebrations this year.’

Buy your own Solarcan at the Old Observatory.

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