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A 1977 album cover from Iceland. (Hrislan Og Straumurinn by Eik)

The explanation of dewars in bold type, posted by Saeed Khademi, is copied word for word from this site discussing medical LOX: www.medox.org/liquid.htm The site appears to be down at the moment but here is a Google cache...

Follow-up, two hours later and there are just a few persistent trails left in the distance to the NW.

Lots of contrails out to the north and west of my location in Hampshire this morning. But looking round to the south at the same time the sky is much clearer: And indeed a patch of drier air is moving up from the south (these photos were taken just before 10am UTC) In another couple...

And over London later this morning, a persistent contrail from a Q400 turboprop in level flight at 25,000ft.

the conditions this morning didn't allow for persistent contrails at normal high altitude so this one looked a bit out of place. By the time I spotted the plane responsible it was no longer leaving a contrail, but it was still below 28,000 feet and climbing: it had only recently taken off...

Jet fuel testing is done on a very regular basis because it has to meet extremely strict requirements. Any out-of-spec contaminants would be a serious problem, both with the risk of engine damage and the alteration of the energy density which would throw fuel calculations off. Jet fuel is more...

A mystery plane left this curving contrail (on the left) over London. Planefinder has some more info: Apparently the CMB callsign is used for US military charter flights: http://www.radarspotters.eu/forum/index.php?topic=3059.0

It must be very frustrating for the people who distrust modern medicine that life expectancy keeps going up, and diseases that would formerly have been death sentences are now easily and routinely treated or prevented altogether. Reality just keeps getting in the way of their ideals.

After a couple of largely contrail-free days they're back this morning. Nice shadow and sundog from the train window. Not 100% sure of the flight but I think it was a private Dassault Falcon at FL410. And, not the best picture, but this trail started almost right in line with the edge of the...

The back end of Katie yesterday evening.

I also noticed lots of cumuliform contrails in Hampshire yesterday. I was out and about with the family so couldn't really check them out but they seemed to be forming as you described, and looked low (not that judging by eye is in any way reliable!) In some cases they looked to be forming...

A friend who is a pilot sent me this photo, taken from the cockpit. This is a Cathay Pacific 777, and the difference in colour between the sunlit and shadowed contrails is obvious.

You are pretty close. The photo was taken at 17.44 BST. I took this one on the bridge itself five minutes earlier, at 17.39: The rainbow was visible for about 15 minutes at varying intensities, with another one appearing half an hour or so later once we had passed through another band of...

The problem with making rain clouds is that you'd need a heck of a lot of moisture. Contrails form cirrus clouds, which contain very little water compared to rain clouds: as can be seen by the fact that they are thin and translucent. The air up where contrails form contains hardly any moisture...

Have you been stalking me? :eek: :D

There was a case recently of a "UFO fleet" photographed in London: It's the same thing - lens reflections of the bright lights at the bottom of the image. Any time you see a mystery light in a photo, look to see what's on the opposite side of the centre point :)

Hello, I am sure this is just lens flare caused by an internal reflection in the camera. A sure sign of this is that the mystery image is directly opposite the centre of the image from a bright light source (in this case the sun). Excuse the very rough sketch done on my phone but this should...

The answer is "it depends". In polar regions, persistent contrails can form at ground level. In temperate zones (eg where I live in the UK), they are rarely seen below about 25,000 feet. But it's impossible to give a hard and fast rule because temperatures and other conditions vary so much.

I tried to look at the pictures but I get an error message saying I don't have permission to see the album. Can you attach them directly to this thread?