Let’s Talk Photography Ep.72 – Atmospheric Optics

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In this solo show Bart walks through some of the cool effects that often go un-noticed in the skies above our heads. We should all be keeping an eye out for these phenomena so we can photograph them as and when they appear. There’s so much more going on up there than rainbows!

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Show Notes:

There’s a lot more in the sky to keep an eye out for than just rainbows!

Our atmosphere can play host to all sorts of cool phenomena for your to photograph. You can’t ever plan for them, but you should always be alert for them so you have the best chance of capturing a truly cool shot.

  • Rainbows — by far the best known atmospheric optical effect! (More on Wikipedia…)
    • Require sunlight shining through raindrops of an appropriate and uniform size
    • Always appear directly opposite the sun in sky — this means rainbows can only appear high in the sky when the sun is low in the sky, so morning and evening are the best times.
    • There are many more things to look out for than just the primary bow
      • The inside of the bow is always brighter than the rest of the sky because of how the light is getting bent by the raindrops
      • There is often a fainter secondary bow visible outside the primary bow
      • If there is a secondary bow, the sky will be noticeably darker between the two bows
      • Sometimes you can see green or pink bows inside the primary bow, these are called supernumerary bows
    • The Moon can produce rainbows too!
    • Bonus Tip the iPhone’s panorama mode can really help you capture rainbows (an example I shot in February 2017 — www.flickr.com/…)
  • Halos — often confused for rainbows because many of them show the spectrum like rainbows do, but they are fundamentally different, caused by ice crystals rather than rain drops, and they appear in different parts of the sky relative to the sun. (More on Wikipedia…))
    • A nice diagram of the most common halos — www.atoptics.co.uk/…
    • By far the most common ice halo is the 22° halo. As its name suggest it appears as a circle around the sun with a radius of 22° (about twice the width of your first held out at arms length)
    • There is also a halo that curves through the middle of the sun known as a Parhelic circle. This is usually quite dim, but where it crosses the 22° halo it produces sun dogs
      • Sun dogs look like tiny snippets of rainbow and they are always 22° out from the sun
    • Sometimes you can see what look like horns at the top of the 22° halo, this is a so-called upper tangent arc. There’s also a lower tangent arc
    • There can also be a subtle rainbow-like arc directly overhead known as a circumzenithal arc
    • The Moon can produce all the same halos the sun can
  • Pillars — like halos, pillars are caused by ice crystals, but as their name suggests, pillars appear as vertical streaks of light above a bright light source. (More on Wikipedia…))
    • Sun pillars are the most common, being visible as the sun rises or sets
    • Any light source can create a pillar under the right conditions, even street lights!
    • A faint sun pillar I captured back in 2009 — www.flickr.com/…
  • Glories — rainbow-like circular bright patches that appear directly opposite the sun. (More on Wikipedia…))
    • only visible from mountaintops of airplanes
    • if your shadow is visible, it will always point to the centre of the glory, producing an effect known as a Brocken Spectre
    • I managed to capture a lovely glory while flying from Brussels to Dublin in October 2016 — www.flickr.com/…
  • Crepuscular Rays — when the sun shines out from behind clouds it can produce striking rays of light radiating out in an arg from the sun. (More on Wikipedia…)
    • If you see crepuscular rays near sunset, turn your back to the sun and look for their opposite number, anticrepuscular rays, rays of light appearing to converge on the point directly opposite the sun in the sky
    • The most spectacular crepuscular rays I’ve managed to capture (a long time ago back in 2009) — www.flickr.com/…
  • Noctilucent Clouds (NLCs) — very delicate wispy clouds that are very high up in the atmosphere. (More on Wikipedia…)
    • Too dim to be seen during the day, only visible in twilight when the sun has set as seen from the ground, but is still low enough below the horizon that the upper atmosphere is being illuminated.
    • Easiest to see late at night looking north from high latitudes around mid-summer when the sun sets but never gets far below the horizon
    • I managed to capture two nice displays of NLCs in 2013:
  • Aurorae — a moving colourful glow in the atmosphere caused by charged particles from the sun interacting with our atmosphere. (More on Wikipedia…)
    • The earth’s magnetic field funnels the charged particles from the sun towards the north and south poles, so the further north or south you are, the better your chances of seeing an aurora
    • The sun’s activity increases and decreases on an 11 year cycle, as do aurorae (we’re currently in a solar minimum 🙁)

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