Coloured light smeared across a darkened wall.
Our house is filled with light - which is great, except when you're trying to get one last hour of sleep at 5.30am. So we got some blackout blinds for the bedroom, temporarily while we get the curtains sorted out. They work really well for me, Just the right level of blind darkness to help me stay snoring till the alarm goes off.
But occasionally, they come away from the window, just a little bit. This morning was one of those times. And then the tiny crack of light creates a camera obscura effect on the wall in front of me. As the breeze gently moves the fabric, so the picture gets sharper and fuzzier. And because the sun comes up on the other side of the house, it's still dark enough inside and light enough outside for the effect to work really well.
The picture above is a fraction of what I can see with the naked eye. It's at the blurry end anyway - and I inverted the image to make the sky be at the top, but it's a dreamy picture of what you can see from our back window, the red tiled roofs and white walls of the houses beyond our back wall. With some experimentation wiggling the blind you can get quite a sharp image - the tradeoff is between the amount of light you let in and the sharpness of the image by limiting the directions that light can enter. At the dimmest end, you can see (but not photograph with my phone) much sharper images of the houses, their windows and roofs and the clouds passing by in the sky.
I'm now tempted to make frames for the front and back windows to fill the room with the images.
If you're wondering what on earth I'm nattering on about, the wikipedia page on Camerae Obscurae explains well how the effect works.