Volcanic dust effects at last! Bishop's Ring on May 18th

On May 17, a cloud of ash erupted from Iceland's now infamous Eyjafjallajökull volcano reached the North Sea area. It led to another temporary suspension of flights over the (western) Netherlands. And this time, there finally were clear visible effects in the sky as well!

The evening of May 17th stood out by being very hazy. Sunset colors were an unusual ochre (see photographs by Dutch KNMI meteorologist Jacob Kuiper here). But more excitedly, both Jacob and I managed to observe (and in my case, photograph) the rare Bishop's Ring.

Below image was taken by me on the late afternoon of May 18th, when remnants of the ash cloud passage still lingered in the atmosphere.

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Visible is a diffuse disc of light around the sun (the sun itself is just behind the roof tip). The outer edges are reddish, the inner part is more bluish, as can be seen from this version where I depicted the RGB color values for two parts of the ring in the color spectrum:

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With "normal" halo's, due to ice particles where refraction is the dispersal mechanism, the blue is on the outside and the red on the inside. Here however, it is the other way around, which confirms it is due to diffraction by dust.

Aircraft-less skies, but is the volcanic dust really visible?

Following the eruption of the Eyjafjallajoekull volcano of Iceland and the large amounts of dust it ejected into the atmosphere, airtraffic over NW Europe, including my country, has been completely halted. For four days now, this has resulted in unique airplane-less and contrail-less skies.

The sky is somewhat hazy for days here now, but is this due to the volcanic dust? Is it visible at all (as it was here after the 1991 Pinatubo eruption, causing pinkish-purple dusk skies)? Dutch news reports on Friday carried many photographs of red evening skies and red streaky clouds, purported to be the "volcanic dust". But all showed what to me looked like normal "evening red", sun-reddened cirrus clouds, and some even showed normal cumulonimbus!

I (and several Dutch astronomy and weather amateurs with me) have watched the evening skies the past days for anything unusual that could be attributed to the dust. But we failed to see anything more than what could very well be normal "evening red". Quite disappointing!

Below image was shot by me on Friday evening 16 April 2010 at about 18:29 UTC (20:29 CEST), some 10 minutes before sunset. Visible is a faint halo in the haze.

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The orange is, in my opinion, normal evening red. And the halo: is it a "normal" halo in cirrus, or is it the "Ring of Bishop", due to dust?

The answer comes from a closer look. I have taken a part of the halo image, and increased the colour saturation to show the colour better. What can be seen (image below), is that the red/orange part of the spectrum is located at the inner side of the ring.

This means the ring is a halo in ice particles: in a dust-induced Bishop's ring, the red should be on the outside.

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Purple volcanic twilights, and KeyHole satellites

Last Friday evening was clear again. Looking outside in twilight, I noted the sky was amazingly purple, due to volcanic aerosols spewn by the Kasatochi volcano in the Aleutians. I walked a few blocks to the Witte Singel canal and shot this picture, with one of the domes of Leiden Observatory silhoutetted in the far distance:

(click image to enlarge)

Later that evening, I captured two Keyholes, USA 129 (96-072A) and USA 186 (05-042A), the Japanese satellite IGS 1A which made a small manoeuvre recently, and a very fine mag -3 flare by Iridium 65. Unfortunately, clouds came in later in the evening.

(click image to enlarge)