Chappuis absorption

[3] Along with Rayleigh scattering, it contributes to the blue color of the sky, and is noticeable when the light has to travel a long path through the Earth's atmosphere.

For this reason, Chappuis absorption only has a significant effect on the color of the sky at dawn and dusk, during the so-called blue hour.

Contemporary scientists thought that Rayleigh scattering was sufficient to explain the blue sky, and so the idea that ozone could play a role was eventually forgotten.

[5] In the early 1950s, Edward Hulburt was conducting research on the sky at dusk, to verify theoretical predictions on the temperature and density of the upper atmosphere on the basis of scattered light measured at the Earth's surface.

Hulburt wished to relate the intensity of light reaching the Earth's surface through Rayleigh scattering to the abundance of particles at each altitude, as the sunlight passes through the atmosphere at different heights over the course of sunset.

His predictions were based on his theory, and on measurements that were made in the upper atmosphere only a few years before by rocket flights launched not far from Sacramento Peak.

[8] Independently of Hulburt, the French meteorologist Jean Dubois had proposed a few years before that Chappuis absorption had an effect on another color phenomenon of the sky at dusk.

Dubois worked on the so-called "Earth's shadow" in his doctoral thesis in the 1940s, and he hypothesized that this effect could also be attributed to Chappuis absorption.

[1] A consistent theoretical explanation of the vibration structure that is in line with the experimental data was for a long time an unsolved problem; even today, not all details of the Chappuis absorption can be explained by theory.