Circumzenithal Arc


It wasn’t the best I had seen, but this display of haloes in the direction of Nelson was better than any I had seen for a few years. I was alerted to it by the sight of a circumzenithal arc high over a rooftop, but then grabbed my camera and found a better view of the western sky.

The circumzenithal arc appears high in the sky when the Sun is low. It is concave up as befits its name: it being a (portion of a) circle centred on the zenith. Below the circumzenithal is the supralateral tangential arc to the 46° halo. It is fainter and is concave down. When the Sun is about 23° above the horizon, the two arcs touch, at which time the colours of the circumzenithal are superb (better than those of a rainbow). When this picture was taken, the Sun was only about 14° above the horizon, the arcs have moved apart and the colours lack the earlier purity.

With a better view, more details emerged. In addition to the mentioned arcs there are other faint features: a 22° halo, a sun pillar, a Lowitz arc and crepuscular rays. Not all that shabby.

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6 Responses to Circumzenithal Arc

  1. Grace says:

    Wow that is a stunning photo Alistair! How do you feel about having your photo’s used as inspirations for paintings?

    • Alistair says:

      Grace, I am comfortable with it. As far as I have been told, my images have inspired maybe a half-dozen paintings, a couple of line drawings, and a tapestry.

  2. birthe says:

    Gorgeous, thank you so much and I do enjoy your explanation of the ‘how and why’.

  3. Carlo says:

    If not quite a textbook on atmospherics optics, at least a good start on a chapter! Sent me scurrying to Google, now digesting a brainful. Very nice Alistair – both the images and the explanations that inspire additional ‘research’.

  4. Kelly says:

    Breath taking

  5. peter bartl says:

    cool stuff! thanks Alistair! peter b

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