Atmosphere

It seems like only yesterday I saw a sun dog. Well, today left me puzzled. I briefly saw an arc in the sky. It was high above the sun, and the wrong way up! I had never seen this before or heard of it so I had to resort to a web search. It turns out it has the wonderful name "circumzenithal arc". As with the sun dog, it is caused by refraction from ice crystals. You can see what sort of ice crystal forms this effect here. It appeared in the sky for about 5 minutes. Fortunately I managed to get a picture. I couldn't quite get the horizon in as well. I estimate that the arc was 40° to 45° above the sun. It had been sunny but there was cloud rapidly moving in from the West. About 10 minutes later I was got drenched as the heavens opened from a grey sky.