sky

sky apparent dome over the earth, background of the clouds, sun, moon, and stars. The blue color of the clear daytime sky results from the selective scattering of light rays by the minute particles of dust and vapor in the earth's atmosphere . The rays with longer wavelengths (the reds and yellows) pass through most readily, whereas the shorter rays (the blues) are scattered. An excess of dust, especially in large particles, causes scattering of many rays besides the blue, and the sky "fades" and becomes whitish or hazy. The sky thus is clearest in winter, in the morning, after a rain, over a mountain, or over the ocean. Leonardo da Vinci experimented with light and attempted an explanation of the sky's blue color. The work on light and its behavior by Sir Isaac Newton, Lord Rayleigh, and other physicists provided explanations of rainbows, sky color, mirages, and other atmospheric phenomena.

sky if the sky falls we shall catch larks proverbial saying, mid 15th century; used dismissively to indicate that something will be attainable only in the most unlikely circumstances.
out of a clear blue sky without warning; unexpectedly (with reference to a ‘blue’ (i.e. clear) sky, from which nothing unusual is expected). Compare out of the blue.
sky-blue pink a non-existent colour; recorded from the mid 20th century.
the sky is falling a warning of imminent disaster, especially one which is regarded as unduly alarmist; the phrase comes from the nursery story in which Chicken Little and other animals repeatedly warn the king that the sky is falling down.
the sky is the limit there is practically no limit (to something such as a price that can be charged or the opportunities afforded to someone).

See also blue-sky, mackerel sky, pie in the sky, winter never rots in the sky.

sky / skī/ • n. (pl. skies) (often the sky) the region of the atmosphere and outer space seen from the earth: hundreds of stars shining in the sky| Jillson had never seen so much sky. ∎ poetic/lit. heaven; heavenly power: the just vengeance of incensed skies. • v. (skies, skied) [tr.] inf. hit (a ball) high into the air: he skied his tee shot. ∎  hang (a picture) very high on a wall, esp. in an exhibition. PHRASES: out of a clear blue skysee blue. the sky's the limit inf. there is practically no limit (to something such as a price that can be charged or the opportunities afforded to someone). to the skies very highly; enthusiastically: he wrote to his sister praising Lizzie to the skies.DERIVATIVES: sky·ey / ˈskīē/ adj. sky·less adj.