Eclipse Optics - Shadow Bands

Clouds at the recent Australian solar eclipse compensated with colourful iridescence and rare shadow bands.

Top:  Lorraine Thompson pictured brilliant iridescent clouds with the sun an unreal narrow crescent and the first diamond ring soon to flash forth.

Lower:  Rob Kaufman captured the first diamond ring itself surrounded by a delicate 'our atmosphere' corona produced by diffraction from water droplets in our own atmosphere as opposed to the unearthly pearly veils of the sun’s corona to come with full totality.     

The diagonal striations – see inset – are rare cloud shadow bands.    The very narrow slit-like solar image is refracted by wavy density fluctuations in the higher atmosphere.   The rays form caustic surfaces that, when projected onto lower cloud or haze, appear as closely spaced parallel bands.    Similar bands are often seen fleetingly on the ground just before the onset of totality.   We do not see bands other than during an eclipse because  rays from the full disk are too divergent.

  "[We were] fortunate enough to see the recent total solar eclipse in Far North Queensland.  The first shot was taken using a Fujifilm FinePix S4500 at 1/600 sec, 54mm, F/7.1, ISO 64 (Landscape Mode - auto).  It shows some of the brilliant cloud iridescence moments before the first Diamond Ring. 

   We were so lucky - the eclipsed Sun moved out of cloud into a narrow gap of clear sky during the first Diamond Ring and stayed in the clear for the whole of totality.  It moved back into cloud at the second Diamond Ring.

   The second shot was taken using a Canon 400D at 1/2000 sec, 200mm, F/7.1, ISO 1600 (I had meant to be shooting at ISO 400 but funny things happen to the best-laid-plans during eclipses!!).  It appears to show the fine striations of shadow bands in the cloud during the first Diamond Ring, The  shadow-band - they show in 3 consecutive frames.   All shots were taken from Clifton Beach north of Cairns, Queensland, 14 November 2012 (local time) or 13 Nov 2012 UT.

   It was an amazing experience, our second total and hopefully more to come!  We're eyeing off the US eclipse in 2017."

     Images ©Lorraine Thompson & Rob Kaufman

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