Cyanometer Sky Blue Grader

Measuring the depth of the atmosphere based on the 1789 de Saussure scale

Match the Sky Color (0-52°)

0° (Cloud/Mist) 52° (Deep Space Blue)

Artist & Designer Specs

Hex Code

#74A6D8

Color Baseline

Cerulean

Atmospheric Grading:

20° Cyan

Observation Tip

For accurate results, observe the sky at a 90-degree angle from the sun. Match the deepest part of the blue, typically found at the zenith during high noon.

🎯 A Simple Example: Grading the Sky at High Altitude

You're on a hiking trip in the mountains, standing at about 2,500 meters (8,000 feet) elevation on a crisp, clear day. The sky directly above you looks incredibly deep and vibrant—almost like a violet-blue. You want to see how this compare to the sky back at sea level.

Just do this:

1️⃣ Stand with your back to the sun so you're looking at the sky 90° away from the light source.

2️⃣ Look straight up at the "zenith" (the point directly overhead).

3️⃣ Use the slider to match the color you see. In high alpine air, you'll likely find it matches around 35° to 40° on the scale.

4️⃣ Notice the "Atmospheric Grading" result: it will likely say "Deep Cerulean (High Alpine)".

5️⃣ Compare this to a typical sea-level sky, which usually grades between 10° and 20° due to higher moisture and dust in the lower atmosphere.

Pro tip: If the sky grades significantly *lower* (paler) than usual for your location, it often indicates an increase in atmospheric moisture or smoke, which can be an early sign of an approaching weather front or distant wildfire!

Data Source: Voyages dans les Alpes • Public domain • Solo-developed with AI

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Lab Notes

The Quest for the Deepest Blue

In the summer of 1787, the Swiss physicist and mountaineer Horace-Bénédict de Saussure reached the summit of Mont Blanc. He wasn't just there for the view; he was there to measure the very substance of the sky. Armed with a circular card painted with 52 numbered squares of blue—ranging from the palest white-blue of the horizon to the nearly black-blue of the high atmosphere—he created the first Cyanometer.

Why and How is This Useful?

Before the advent of modern laser-based LIDAR and satellite spectral analysis, the Cyanometer was a cutting-edge scientific instrument. De Saussure’s logic was brilliant in its simplicity: he hypothesized that the blue color of the sky is caused by suspended moisture and particles (aerosols) reflecting light. Therefore, a deeper blue indicated a cleaner, thinner, and drier atmosphere. By matching the sky to a specific degree on his scale, he could estimate the transparency of the air and the probability of incoming weather changes.

Today, while we have digital sensors for everything, the Cyanometer remains a powerful educational tool for visual literacy. It teaches the observer to look past the generic label of "blue" and see the subtle gradients of the atmosphere.

Modern Application

In the contemporary world, the Cyanometer has found a second life among landscape painters, photographers, and "analog meteorologists." For a plein air artist, matching the cyanometric degree is essential for capturing the correct atmospheric perspective. For photographers, it provides a historical baseline for understanding how UV light and elevation affect color saturation. In 2026, as we seek to reconnect with our physical environment, these manual methods of observation offer a meditative and scientifically grounded alternative to glancing at a weather app.

Bridging Data to Today

This digital implementation preserves the 52-degree scale of de Saussure’s original device while providing a reactive interface. As you move the slider, the central "lens" matches the specific HSL (Hue, Saturation, Lightness) values that correspond to the historical descriptions of alpine sky depth. It allows you to transform a simple visual observation into a data point, bridging the gap between 18th-century mountain expeditions and modern digital utility.

P.S. The human is holding a blue card up to the window again. I tried to help by matching the color of my favorite blue yarn ball to the sky, but the yarn is much more interesting because it moves. The sky just sits there. If the sky is so "deep," why can't I hide my toy mouse in it? 🐾