Update: Now breaks my wooden shoe. http://www.atoptics.co.uk is back online. Our prayers have been heard (and Les Cowley is now a redditor)! Blimey, this is good news, honestly. Thank you, Les!
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I’m doing this one in English because it’s important, at least for those interested in atmospheric optics: halos, sundogs, rainbows, iridescent clouds, glories, light pillars and every other wondrous thing to look for when light meets the sky (or ground. Or water. Or soap bubbles. Or butterfly wings).

Several weeks ago, it was noticed that the number 1 authoritative online resource on the topic for the past 24 years, http://www.atoptics.co.uk, was suddenly down. My hope was that this was temporary and due to the founder, the magnificent Les Cowley, having decided to do some updating, cleaning or otherwise twenty-first-centurifying the site.

But alas, it now turns out that he has consciously decided to take the website down for good. Read about it here at the atoptics subreddit (which Blinde Schildpad and I co-founded back in 2012, although neither of us have been active members for a long time). The site has even been excluded from archive.org, meaning that Atoptics is simply gone forever.

Apparently Les is disinclined to elaborate on the reasons for his decision (though this comment probably gets the gist of it), which he has all the right in the world to be, but in total earnest: this is a serious loss for the entire community of optics enthusiasts. The website was an unsurpassed treasure trove on the topic, teeming with photos, information, applets, research, diagrams and whatnot on the ins and outs of every optical phenomenon imaginable and the physics underlying them. Aw! Bummer. This was the site that got me looking at the sky!

Bummer indeed. Now where should we enthusiasts go, or send the uninitiated? Of course, heaps of decent information on atmospheric optics can be found scattered elsewhere across the web and in these things called “books” (See the list at the bottom of this post) and the subreddit gang are discussing setting up an alternative so who knows what’ll grow out of the ashes, but it will be hard to come even close to a place that presented everything so thoroughly, attractively and comprehensively in one spot as Atoptics did.

So, yeah. Thank you, Les (honestly), for the beautiful things you have given us, and may the Brocken Spectre haunt you (just a little) for taking them away from us again. Let a new generation arise and carry forth the legacy!

Alternatives
Some online alternatives of varying decency include:
- The Atoptics subreddit (unaffiliated with Les Cowley, we just nicked the name)
- Atmospheric Phenomena (ditto, probably)
- Glows Bows and Haloes
- Sky Warden (Taivaanvahti)
- Halo Phenomena
- Submoon
- Pixheaven
- Paraselene
- (In German) Arbeitskreis Meteore
- (In Dutch) Meteo-Julianadorp
- [sigh] Wikipedia
These are some pretty good books on the topic:
- Marcel Minnaert – Light and Color in the Outdoors (translation of De Natuurkunde van ’t Vrije Veld, part 1). Old, but still good.
- David K. Lynch & William Livingston – Color and Light in Nature
- (In Finnish) Marko Riikonen – Halot. Haven’t read it (which might have something to do with it being in Finnish) but it’s in Finnish so it’s bound to be good.
- (In Dutch) Janneke Schenk – Over de Regenboog. This one deserves more attention and an English translation, as it’s basically the essentials of atoptics.co.uk in book format.