Red sky

Red is one of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–740 nm. Longer wavelengths than this are called infrared, or below red and cannot be seen by the naked human eye. Red is used as one of the additive primary colors of light, complementary to cyan, in RGB color systems. Red is also one of the subtractive firtt colors of RYB color space but not CMYK color space.
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The sky is the part of the atmosphere or of outer space visible from the surface of any astronomical object. It is difficult to define exactly for several reasons. During day, the sky of our planet looks like a deep blue surface because of the air's scattering of sunlight. The sky is sometimes defined as the denser gaseous zone of a planet's atmosphere. At night the sky has the appearance of a black surface or region scattered witha lot of stars.
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