A fall of snow and the afterglow.

[venta]

Humph. mejoff promised me snow yesterday, and it never turned up. The sky in Reading is toying with me, alternating between a grey, bodey snow-promise colour and a cheerful blue with little fluffy clouds. To rub it in, the traffic reports this morning suggest that my home town of Darlington has lots of snow.

The BBC forecast for Reading says it's snowing now. It lies :(
(Can it be a forecast if the period covered has already started ? It's clearly not a report. An aftercast ? Nowcast ? Guess ? Outright lie ?)

Update: Oh, right, so even London has snow now. That's just adding insult to snowlessness.

And I also have a request for any scientific brains out there:

On the way back from Leyland last weekend, Jane, who's about 15, was looking out of the car window at a rainbow. Without warning, she suddenly asked "Why are rainbows curved?"

Now, I've got an A-level in physics, I reckon I should know the answers to questions like that. But I don't.

My mother, who has had way more practice at fielding random trivia requests from teenagers, calmly said "Because the surface of the earth's curved." Which didn't sound all that plausible to me, because the curvature of the earth and of an average rainbow are very different.

So. Why are rainbows curved?

The best I've managed so far is that the layer of air close to the earth has bands of different temperatures, which curve with the earth, and that air at different temperatures causes different amounts of refraction of light. Which is a bit vague, and I'm not very happy about it. And don't feel it really qualifies as an explanation.

Can anyone provide a coherent and convincing explanation ? (Of their own - I'll try googling in a bit.)

Grr. Very stiff hands this morning. Too much rapper at the weekend - we're practising for the national competition in a fortnight.

Comments

[neilh.livejournal.com]

Given these explanations, and a little thought, I'm guessing that all rainbows are the same size, too. And at the same optical distance from the observer. I wonder how you'd go about demonstrating that in a scientifically rigorous way?

[wimble.livejournal.com]

What determines the size of a rainbow? [Scientific American]

[neilh.livejournal.com]

That only really talks about apparent size, rather than actual size (but then, I'm not sure they really have an actual size, being an optical effect)

[onebyone.livejournal.com]

And at the same optical distance from the observer

No, because if there's enough water in the air then the rainbow can always appear "in front" of stuff that you might think ought to obscure it on account of the way it usually appears to be anchored at or around the horizon.

So if you only count rainbows caused by rain, not those caused by waterfalls or hoses, the closest I've ever seen the end of a rainbow is about 20 yards away or so. I didn't notice any gold, leprechauns or the like.

[neilh.livejournal.com]

Doh, you let them get away?