Measuring the Blueness of the Sky

 

The Cyanometer, an instrument invented in 1789 by Horace-Bénédict de Saussure and used by the famous explorer Alexander von Humboldt to measure the blueness of the sky. Originally a scientific tool used to study the atmospheric moisture and particle content, a darker blue reading indicated less water vapour, while a lighter, whiter blue suggested more moisture or pollution.  The original design consisted of 52 or 53 shades of Prussian Blue on a circular card. Contemporary interpretations of the cyanometer have appealed to artists, particularly as a guide for accurately mixing sky colours in paintings. They range from DIY YouTube tutorial videos using watercolours to studies of the optimal combination of modern pigments needed to simulate the sky's full chromatic range.

This video was prepared by an AI, Google’s Notebook LM, to summarise some key sources that collectively establish the cyanometer's historical significance, its scientific function, and its continued relevance as an artistic and educational tool for studying colour and the environment.