Astronomy Picture of the Day is an excellent resource of some of the best astronomical pictures available from both professional and amateur astronomers alike. And ever so often cool things in astronomy and photography come together and appear on APOD also.
No exception is today’s offering of a solargraph taken with a pinhole camera. The pinhole camera is actually a coke can with a small hole at the end. The hole is so small that only a very small amount of light can get to the focal plane where the image is formed. Justin Quinell set up his pinhole camera on the Clifton Suspension Bridge in Bristol, UK, and kept it exposed for 6-months between Dec 17, 2007 and June 21, 2008. That is the time between the winter and summer solstice when the Sun is at its lowest and highest points in the sky, respectively (winter solstice is actually 21 Dec). This is different to, and should not be confused with, an Analemma.
What you see is the day-to-day tracks of the Sun across the sky, and how it gets higher in the sky each day. You also see the days when it was cloudy from the gaps in the sun trails. And because the exposure was so long, eventually the bridge and the river it crosses also starts to form an image. Altogether cool, I think.
I would have loved to have shown the image here, but I’m not sure that the APOD copyright allows me to. You can see more of Justin’s work here.