The leading cause of an unclear sky, a bit like today, is the collection of billions of small water droplets that produce clouds. We all know this right? So, lets hear some facts that you may not know:
Cloud droplets generally have diameters in the range of between 0.01 and 0.02 millimetres, with the largest reaching 0.15 millimetres (not to be exact). Typically, it takes a million cloud droplets to form the smallest rain-drop - a drizzle droplet - with a diameter of 1.2 millimetres.
Such small droplets have a size comparable to, or maybe slightly larger than, the wavelengths of visible light and they can therefore interact with the light waves through a process known as 'diffraction'.
Diffraction occurs when a light wave's path bends around an object or objects of a similar size to its wavelength.
As a wave, light can interact with other light waves, forming combination patterns. The most important interactions are constructive and destructive interference. In constructive interference, the two waves add to produce an enhanced condition characterised by increased brightness of bands of spots. In contrast, destructive interference degrades the overall light quality, resulting in dark bands of spots.
The interaction of light with small water droplets through diffraction produces two distinct types of natural wonders, which characterise coronas and glories. Other optical wonders include our well known rainbows, crystal orbs, haloes, sundogs, arcs, tangents, circles, light pillars and others.
Each of these are a truly amazing visual experiences with far greater complexity and detail that I cannot even go in to explaining without having days and lots of reference texts, however I wanted to make a point of sharing with you how a single water droplet and light can make some of the most breathtaking visual experiences we will ever witness...
Truly awesome stuff ;)
http://www.elightspot.com/lights-and-matter-a-guide-to-optics.aspx
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