Extract from the weather journal

Lights in the sky

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Many beautiful optical effects can be seen in the atmosphere, including halos, coronas, rainbows, auroras, iridescent clouds, the colour of the sky, the green ray, crepuscular rays, and sun pillars.

Halo: A luminous ring around the sun (solar halo) or moon (lunar halo), mostly whitish but sometimes showing the colours of the spectrum. Haloes are formed by the refraction of light by ice crystals in cirroform clouds (cirrus, cirrostratus and cirrocumulus).

Corona: A luminous crown around the sun or moon. The inner part may be bluish, whitish, or yellowish, or faintly show all the colours of the spectrum. The reds are always at the outside. Coronas are formed by the diffraction of light, generally by water droplets.

Rainbow: Caused by the refraction and reflection of sunlight by falling raindrops. The colours of a bright rainbow run from violet to red. Rainbows vary considerably according to the strength of the light and the size of the drops.

Aurora: The aurora australis is sometimes seen in the night sky over southern Australia - mainly in winter. It usually appears as a bright arch. Streamers of light frequently radiate from the arch and sometimes extend beyond the zenith. Occasionally the arch resembles a swaying curtain. The aurora is an electrical phenomenon usually associated with magnetic storms.

Crepuscular rays: Formed when the sun illuminates dust particles in the atmosphere. When the sun is low, the shadows of clouds - or mountain peaks - are thrown across the sky. As the dust particles in the shadows are much darker than those in sunlight, a series of irregular bands, alternately light and dark, are produced. Crepuscular rays are seen at their best just after sunset.