You may recall that in my past employment, I worked for a company that was owned by a window manufacturer. Although I had exceedingly little to do with the owners' window business (by choice from BOTH ends), I still learned many details about windows. One of the more interesting aspects was what could happen when the exactly right combination of window, temperature(s) and sunlight all came together unexpectedly. In those rare sets of circumstances, you could have the window glass curved in a concave manner so that it focusses the sunlight to produce an intense beam, jokingly call "The Death Ray". Sometimes it's hot enough to melt vinyl siding and othertimes it's hot enough to burn human hair.
This last weekend, I had my own "death ray" in the backyard of my house. Take a look at this picture:
What is even more intriguing is this close up of a caustic:
I've been waiting all winter to get these pictures and it hasn't been easy. We've had an endless stream of cold followed by snow followed by cold followed by...which has prevented these tracks from being visible on a weekend so that I could take the pictures. Things finally worked out for me. If I had daily midday access to this site (I don't due to work hours), it would be fun to cover one of the windows with cardboard and remove it for a few minutes at noon each day. The spots that would melt the ice would then take the partial shape of the annalemma (reversed due to the reflection the light undergoes).