Wednesday, 11 August 2010

Miraged sunset

From atop Mauna Kea several inversion layers out to the west over the Pacific Ocean are noticeable due to their effect on the sunset. This evening's sunset was difficult to photograph as the winds were as high as 40mph, so I didn't bother with trying anything too spectacular, but did try and capture the setting sun with short exposures.

If you look closely (click on the image for a larger version) the upper and separate part of the sun (a mirage) is caused by refraction in a strong inversion layer. The layer holds air of a different temperature than below, hence has a different density therefore a different refractive index (remember your physics lesson at school?).

Several weaker inversion layers can also be seen distorting the disk of the sun as it sets behind very distant clouds. Eventually, the mirage disappears as the sun disappears behind the clouds and it's time to start another night on the mountain.

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