Oil Film Rainbows

I came across these striking colors in a parking lot shopping for lamps for our New York apartment; we're going down Wednesday and will take them along.

It had rained earlier and the asphalt was still quite wet, providing a good surface for the oil to spread on. There were nearly two dozen of these spots, up to perhaps half a meter across, forming a irregular trail where someone had passed with some sort of dripping oil. When we came out of the store after about 30 minutes, it had begun to rain and most of the spots had disappeared.

This illustrates key aspects of the course on light and optics which I audited over the past couple of months--a good explanation on the internet is here.