fast bloke

Why are rainbows arched?

ajm

refraction of the light through the raindrops!

De Warrenne

really they're round, only the earth gets in the way (not if you see them from a plane tho' )

So, what your seeing is part of the effect of the sun being refracted through lots of rain

boxst

Hello

Because the gold at each end weighs down the rainbow that is pinned to the sky so it creates the arch.

(real answer:Rainbows are arched because of a ray of light that enters a water drop on one side and then as it enters is refracted. While inside it reflects off of the opposite side of the water drop and once again is refracted as it emerges from the opposite side of the water drop creating the 'arched' rainbow that we see.)

Steve.

Jerome

This is my favourite explanation. Not to mention the only one I understand.

fast bloke

I understand the bit about refraction, but that doesn't explain why it is curved/round - you would think that using refraction only, each raindrop would appear as an individual prism, with no overall organisation....


I think I'll tell her about the gold

TelBoy

Otherwise they wouldn't have pots of gold at either end - THAT'S what you tell a 5 year old.

TelBoy

Spooky!! Maybe we should post in Muppets occasionally...

suprabeast

Each raindrop is spherical shaped therefore when the light is refracted, it will be refracted in a spherical shape too on exit. Therefore your half circle. The only reason theres half has been covered earlier

fast bloke

mmmmm - just got the answer from an applied maths lecturer - along with 14 pages of proof

each raindrop is an individual prism.(see I'm not that stoopid) It seems that you can only see the refracted light in the ones that are at 42 degree angle between the viewer, the raindrop and the sun.

Cool - I'm gonna get her to ask me another one

ajm

This is because each drop bends the light by the same amount so you will only see rainbow light coming from drops that are placed such that the angle between you, the drop and the sun is constant and that happens to be the curve you see!

It is also the reason why you can never actually reach the end of a rainbow, because as you move, the angle changes and therefore different droplettes make up the rainbow and your happy dream of a crock of gold turns rapidly into a crock of $hit!

suprabeast

rainbows - "i hate them... the walk on in.. and crawl up your leg!"

Markus

A bit of info on them (Can't see a mention of Alexander's dark band in there though )

RB5193

Because if they weren't they'd be called RAINFLATS otherwise

RichWalk

Good answer

julian N/W wrx my93

this question was in Focus magazine this month.......

ozzy

did I hear SN let out a huge groan?

now a square rainbow would just look feckin stupid.

ajm

To be honest I'm surprised a 5 year old didn't know such a trivial fact. School standards must be slipping!

TEXAS PETE

Next time it sunny get the sprinkler out and you little five year old can see the whole rainbow

fast bloke

Strangely, her mother thinks I go to far when she asks stuff like this eg

Why does it rain
Mother - it rains to make plants grow so we can eat
Me - erm - actually it rains because the sun shines on the sea and some water evaporates etc etc etc. - AS A RESULT of it raining, plants grow and we can eat
Mother - schlaap
me :nods: and shuts up

mj

something I remembered something from school - is that the angle of incidence? it is the angle at which light decides wether to enter an object or bounce off it.

ajm

Almost, the angle of incidence is the angle at which the beam hits the lense/prism etc. You are thinking of the critical angle.

mj

X2/

boxst

Hello

That's extremely good (apart from the shutting up bit). I just spent 5 minutes wandering through Waitrose with my 4 year old daughter explaining the use of the word "I" within a sentence.

If more people tried to educate their children by proper explanations everyone would benefit.

Steve.

boomer

Going back "mumble" years ago, i did a 240 foot freefall abseil down Alum Pot in the Yorkshire Dales (just up from Horton in Ribblesdale).

The sun was high in the sky, and shone down the opening, so i could see my (and the rope's) shadow on the vertical wall.

There is a waterfall into the pot, which created a fine mist as it fell - just the sort of droplets to create a rainbow.

Thus, due to the physics and refractions etc. mentioned above, i saw a rainbow as a perfect circle (there was no "ground" to interrupt it) - with my shadow in the exact centre. It is a surreal sight - if only i had my camera. It certainly helps you understand how rainbows work

mb

jasey

Maybe being over simplistic here - but could it have something to do with the shape of the Sun ?


I love all this stuff about prisms and angles of incident and all that good stuff but I reckon you should tell your daughter it's cos the Sun's round .

Edcase

OOOOOOOOOOOooohhhhh, you mean rainBOWS!!!!!!



I'm with ya dude...

catherine666

Rainbows are always arched because a ray of light enters one side of a water drop, gets refracted as it enters, reflects internally of the other side of the drop and emerges from the other side, again with refraction.