PerEwpa, literally " things in the air," from yerb., beyond, and a€ipav, to lift up), a term originally applied by the ancient Greeks to many atmospheric phenomena - rainbows, halos, shooting stars, &c. - but now specially restricted to those luminous bodies known as shooting stars, falling stars, fireballs and bolides.
The Vernal, about half a mile below the Nevada, is famous for its afternoon rainbows, At flood-time it is a nearly regular sheet about 80 ft.
In the first class we have halos, and coronae, or "glories," which encircle the luminary; the second class includes rainbows, fog-bows, mist-halos, anthelia and mountainspectres, whose centres are at the anti-solar point.
The impurity of the colours (due partly to the sun's diameter, but still more to oblique refraction) is more marked in halos than in rainbows; in fact, only the red is at all pure, and as a rule, only a mere trace of green or blue is seen, the external portion of each halo being nearly white.
Formerly classified by the ancient Greeks with halos, rainbows, &c., under the general group of "meteors," they came to receive considerable attention at the hands of Descartes, Christiaan Huygens, and Sir Isaac Newton; but the correct explanation of coronae was reserved until the beginning of the 19th century, when Thomas Young applied the theories of the diffraction and interference of light to this phenomenon.