Spending some time at school during the holidays has got one advantage: You discover interesting phenomena involving the sun and clear skies. (Remeber the sun dogs I saw last October?)
A couple of days ago I helped two students preparing for a competition. They have built a water rocket, and while we observed the rocket’s flight, we discovered what looked like a small, upside-down rainbow almost straight up.
Turns out it’s a circumzenithal arc (see also here) which is created by the sun’s light refracted in small ice crystals high up in the atmosphere. I took a picture, but it doesn’t really do the phenomenon justice, so check out Eva Seidenfaden’s circumzenithal arc photos.
You can’t see the arc well in the thumbnail, so click for the larger version. – Klick für die Vergrößerung, auf der man den Bogen besser erkennen kann.