Imaged by Dan Ackroyd at Kirribill, New South Wales, Australia.
©Dan Ackroyd, shown with permission
"One day in Kirribilli I went for a little wander with my camera, to see what I could see and maybe take a photo of it.
After not having walked very far I noticed out of the corner of my eye that the Sun appeared a bit unusual. I couldn't see it very clearly, as the Sun was so bright, but it seemed that there were rainbow colours around the Sun.
I took just a couple of pictures, trying to get a good tree trunk in front of the Sun to prevent it from burning my camera (or eyes) too much. Because I'd hurt my eyes a bit by looking at the Sun (I recommend not doing that) I only took a couple of shots, and couldn't really see what the picture looked like on the little camera screen.
When I got home I realised that I'd taken a picture of something a bit unusual. It's a corona which is formed when light is diffracted through very small particles, almost certainly water droplets in this case.
It's possible to figure out what the size of the water droplets is from the angular size of the corona they produce, so I made this web page to do that. The full-size image can be seen on my Flickr page."