Scientists have explained a key truth: they revealed why the sky appears blue.

The blue color of the sky, despite its apparent simplicity, is the result of a complex interaction of sciences, primarily physics and chemistry. The colors we observe in nature arise from various processes, and the blue of the sky is a direct result of the interaction between sunlight and the Earth's atmosphere. Scientists have explained the complexity of this seemingly simple phenomenon by revealing all the processes that lead to it, as noted by The Conversation.

The Earth's atmosphere is mainly composed of nitrogen and oxygen molecules, which are incredibly small — measuring about 0.4 nanometers, explains Daniel Friedman, dean of the College of Science, Technology, Engineering, Mathematics, and Management at the University of Wisconsin-Stout. For comparison, approximately 250,000 of these molecules can fit on a single strand of human hair.

When sunlight enters the atmosphere, it encounters these molecules. This interaction leads to a process called scattering, where molecules absorb light and then quickly re-emit it in random directions. Blue light, due to its shorter wavelength, is scattered much more effectively than other colors, which is why the sky appears predominantly blue, says Friedman.

This phenomenon, first explained by British physicist Lord Rayleigh in the 1870s, is now known as Rayleigh scattering. While other atmospheric gases, such as carbon dioxide and methane, affect the planet's climate, their impact on the color of the sky is minimal. If Earth had no atmosphere, like the Moon, there would be no scattering, and the sky would appear dark even during the day.

The lunar sky, as seen in images from space, sharply contrasts with the bright blue of Earth. A rainbow, which represents the full spectrum of visible sunlight (red, orange, yellow, green, blue, indigo, violet), perfectly illustrates how sunlight interacts with particles. Water droplets in the atmosphere separate sunlight into its constituent colors, with blue light being scattered most effectively.

The color of the sky changes depending on the position of the Sun, explains Friedman. During sunrise and sunset, sunlight passes through a denser part of the atmosphere. This additional distance scatters most of the shorter wavelengths, such as blue and green, leaving the longer wavelengths — red and orange. These hues create the unusually beautiful skies observed at dawn and dusk. The same principle of Rayleigh scattering explains why, during these times, the sky transitions from the daytime blue to fiery tones at the horizon.

Colors have always held great significance for humanity, whether as subjects of scientific study or as means of creative expression. They not only shape our perception of the environment but also influence how we interact with it — from painting landscapes to choosing clothing. On a deeper level, understanding and studying the science of color uniquely connects us with the natural processes that have fascinated humanity for centuries.

This material is for informational purposes only and does not contain advice that may affect your health. If you are experiencing issues, please consult a specialist.