Monday, October 27, 2014

Optics, Atmosphere & Astronomy

Several atmospheric phenomena exist that usually catches our eye. They usually result from optical effects in the atmosphere such as refraction, diffraction, scattering, etc. The most commonly known atmospheric effect is that of rainbows. The presence of water droplets in the atmosphere causes the sun's light to be reflected and refracted into its component colors. Here are some other atmospheric effects:

Cloud Iridescence - this rainbow colored cloud results from diffraction of light by tiny water droplets or tiny ice crystals. Diffraction is the process of bending light around an object.


Corona - Coronas are 'crowns' of light around the Sun or Moon. This process results also from the diffraction of light. Diffraction generates interference patterns that disperses the light outwards and sometimes into its component colors.

Halo - results from refraction of ice crystals in the upper atmosphere (cirrostratus clouds). The ice crystals are usually formed as a result of a LPA (low-pressure area) hence it is usually associated with upcoming rain or cloudy weather.

Silver Lining - another diffraction result that happens in the edges of clouds

Blood Moon - a total lunar eclipse results from atmospheric lensing. The atmosphere of the Earth acts like a lens that bends light. The component of the visible spectrum that is bent the most is that of the red end of the spectrum. So as the Sun-Earth-Moon alignment happens the red light is bent by the Earth's atmosphere and shines on the surface of the Moon. You can actually see the same effect happening as the Moon rises opposite to the Sun. Close to the horizon the Moon appear reddish orange and then turns yellowish as it continues to ascend and finally into the normal hue once it is no longer affected by the lensing.

Some atmospheric optics are more common than you think:

Blue Sky - The blue color of our sky is a result of Rayleigh Scattering or the scattering at certain wavelengths. Molecules of Nitrogen and Oxygen in the air are effective at scattering the blue component of the visible spectrum so light from the Sun is scattered in all directions.

White Clouds -  another scattering phenomena known as Mie Scattering. This results from cloud droplets of sufficient size (approximately 20 micrometers) being able to scatter light at all wavelengths.

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