Astronomy magazine, saying “As the Sun set one evening, I observed a sword-like column of light pointing straight up from the horizon. What was it?” This appeared in the December 2008 issue, with the reply that “What you saw is called a Sun pillar. This vertical shaft of light extends upward from the Sun. It's usually observed at sunrise or sunset. Sun pillars form when sunlight reflects off the surfaces of falling ice crystals...”
Sun pillars are also mentioned in the first book I reviewed for Fortean Times, back in the January 2012 issue – Fireballs, Skyquakes and Hums by Anthony Milne. I found the book’s technical explanations rather erratic, which is why I only gave it a rating of 7 out of 10, but it’s a useful source of data on unusual aerial phenomena – or at least, it is for those of us who don’t think an unusual aerial phenomenon has to be an extraterrestrial space vehicle in order for it to be interesting.
Of course, you can never underestimate the devout UFO believer’s ability to see extraterrestrial space vehicles in any unusual aerial phenomena... even ones that don’t look anything like space vehicles. I was surprised, though I probably shouldn’t have been, to see in the Wikipedia article about sun pillars that “light pillars have also been known to produce false UFO reports”.
Another naturally occurring phenomenon that really does look quite UFO-like is the saucer-shaped lenticular cloud. Ewa sent me a rather impressive example of one of those too. She took this photograph during a hiking trip in the White Mountains of New Hampshire in July 2011:
Arcus Roll Cloud. This was unusual enough that it even made the local newspaper (the Dorset Echo): “Concerned residents in Portland and Weymouth thought they were being hit by a tornado during a dramatic thunderstorm...” Here is one of Peter’s own photographs of the roll cloud, taken from almost the same vantage point as the lenticular cloud above (although with a wider field of view):