Nacreous clouds

Photo: María H. Tryggvadottir

We enjoyed some fascinating "Nacreous clouds" or "polar stratospheric clouds" also known as mother-of-pearl clouds, this weekend. This special phenomenon occurs mainly at high latitudes during the winter when temperatures in the stratosphere fall below the frost point. They are best observed just after sunset or when the Sun is between 1 and 6 degrees below the horizon in northerly latitudes.