How cold does it have to be for air to freeze?

[slinkycat]

Beautiful sunny day here today, no snow but the hoar frost has been increasing since yesterday and is now about an inch long.
The air looked like it was full of glitter and I realised it was freezing, never seen it like that before. Our thermometer said -4c but I'm not sure if its accurate, and I couldn't seem to find a relevant answer on google.

[Buenchico]

78% of air is nitrogen It will liquefy at -196C and freeze at -210C.

21% of air is oxygen. It will liquefy -183C and freeze at -219C

What you're seeing is water vapour which will freeze at 0C.

Chris

[slinkycat]

Thanks both, wish I'd worded the question a bit better though, I had realised there must be moisture in it that was freezing and not the actual air itself, feel a bit daft now!
That temperature of 0C surprises me though Chris, it must happen quite often but I can't recall seeing anything like it before.
Maybe it was the particular conditions today with the blue sky and bright sun that made it so visible.
Anyway it looked magical:-)

[mollykins]

And if it's sunny the light reflects off of the crystals . . .

[gen2]

What you were seeing is what meteorologists call 'Diamond Dust'.

[DTCwordfan]

and when the wind gets up, do meterologists call that a ***

[DTCwordfan]

the auto-ed worked - a bl-- job

[snowyball]

hello slinky

have you seen the film "day after tomorrow?" ....