Why is the Sky Blue?

Pelorus Guardian and Miners' Advocate., Volume 29, Issue 41, 29 May 1917, Page 2

Why is the Sky Blue?

THE WONDERS OF LIGHT

Sunlight, which we call white, is composed of light rays of different colours —red, orange, yello.v, green, blue, indigo and violet. It can be broken up into its constituent colours in various ways. If it passes through a transparent prism (like the crystals that hang from a chandelier) or if it falls on a surface which has almost invisibly minute irregularities (like mother-of-pearl or the wing of a butterfly) we see the rays into which sunlight has been separated. These phenomena are observed when light is not absorbed. Hold a piece of red glass in front of a flame and we see only red. Hays of all other colours have been absorbed. The natural colours of the objects we see about us, leaves, Powers, books, and chairs, depend upon absorption. A green leaf sends back chiefly green rays ; the rest are absorbed. So the natural colour of everything in nature is the une-seab-ed residue from full white light, there is no such thing as colour by itself.

A swarm of minute particles, scattered in the path of white light, will break it up, like the surface of mother-of-pearl. If the particles happen to be of just the right size and the spaces between them just the right distance, they will absorb rays of one colour only and throw of! the rest. The atmosphere is fill*'*! with countless dust particles, and their size and spacing is such that, they scatter rays which we call sky Mue. Nearer the horizon, larger particles turn the blue into white ; thin happens above a dusty town mm whore mists or clouds hang above us. All ' .at is left of white sunlight, after passing through many miles of bluescattering air, appears in the hues of sunset. The size and spacing of dust particles as well as the angle at which sunlight strikes them, determines the colour of the sky. On the moon where there is no atmosphere and no dust, the sky is jet black at noon. The sun appears as a vividly glowing disc in an inky canopy. That is also true of the vast space which exists between the stars.