If there was no atmosphere, what colour would the sky be visible from the Earth?

Without an atmosphere, the sky visible from Earth would appear black [A]. The blue color of the sky is primarily due to Rayleigh scattering, where shorter wavelengths of sunlight (blue and violet) are scattered more effectively by atmospheric gases than longer wavelengths (red and orange). This scattering phenomenon gives the sky its blue appearance during the day. In the absence of an atmosphere, there would be no scattering of sunlight, and thus no preferential scattering of blue light. Instead, sunlight would travel directly to the Earth’s surface without significant alteration in color perception. As a result, the sky would appear black to an observer on the ground, similar to how space appears black to astronauts in orbit. This hypothetical scenario helps illustrate the crucial role that atmospheric composition plays in shaping the appearance of the sky and the overall visual experience of Earth’s environment.