During daylight hours, the sky above us has a bright blue hue, and when the sun sets below the horizon, it is colored sometimes crimson, sometimes pinkish, and sometimes golden. The roots of this phenomenon might seem obvious, but the reality is more complex. We will explain the scientific principles that determine the palette of the sky and why the shades are what they are. What is the reason for the blueness of the daytime sky and the crimson at sunset? © jannoon028/Freepik The solar stream appears white to us, but this is an optical illusion. In reality, white light is a composition of all the spectral components: red, orange, yellow, green, cyan, blue, and violet. In outer space, the rays travel without dispersal. But as soon as light penetrates the Earth’s atmosphere, it interacts with gas molecules and suspended dust particles. Here, a physical law comes into play. The colors that make up the light have different wavelengths. Red is long-wave radiation; it can easily bypass small obstacles and passes through the atmospheric envelope almost unchanged. Short waves are inherent in blue and cyan. When colliding with air molecules, the short waves of blue and cyan begin to scatter intensely in all directions—this process is called Rayleigh scattering. This peripheral light is what you perceive when you look up. The sky appears blue because the atmosphere acts like a “sprayer” that scatters this color more actively than all others. But why then does the sunset take on a red hue? As evening approaches, the Sun moves towards the horizon line. The rays have to travel a significantly longer path through the layers of the atmosphere to reach the observer’s eyes compared to midday. During this journey, almost the entire blue and cyan parts of the spectrum manage to scatter to the sides without reaching the Earth’s surface. Only the long waves—red and orange—reach the witness’s eye. If there is a significant amount of dust or moisture in the air, for example, after a hot spell or before a thunderstorm, the sunset will be even more intensely red. Larger particles carry out an even more effective filtration of colors. Thus, the crimson glow on the horizon is not a harbinger of misfortune but merely an indicator that the light had to break through a dense atmospheric layer.
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