Why a bow?

Opus the Penguin

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Jun 6, 2006, 12:45:47 AM6/6/06

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The boy wanted to know what makes a rainbow. I explained about the
water droplets creating a prism. But he wanted to know why it forms an
arch as opposed to, say, a multi-colored sheet.

For myself, I still don't quite get the prism deal. Each individual
droplet isn't acting as a prism, otherwise you'd get thousands of tiny
rainbows that wouldn't really be visible from a distance. Instead, a
whole big group of them are banding together to create a giant prism
visible from miles away. How do they get organized to do this?

--
Opus the Penguin
The best darn penguin in all of Usenet

Tim Wright

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Jun 6, 2006, 12:58:22 AM6/6/06

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Opus the Penguin wrote:
> The boy wanted to know what makes a rainbow. I explained about the
> water droplets creating a prism. But he wanted to know why it forms an
> arch as opposed to, say, a multi-colored sheet.
>
> For myself, I still don't quite get the prism deal. Each individual
> droplet isn't acting as a prism, otherwise you'd get thousands of tiny
> rainbows that wouldn't really be visible from a distance. Instead, a
> whole big group of them are banding together to create a giant prism
> visible from miles away. How do they get organized to do this?
>

This explains it far better than I could.
http://science.howstuffworks.com/rainbow.htm

--

Tim W

"Money frees you from doing things you dislike. Since I dislike doing
nearly everything, money is handy."

Groucho Marx

Blinky the Shark

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Jun 6, 2006, 1:15:32 AM6/6/06

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Opus the Penguin wrote:

> The boy wanted to know what makes a rainbow. I explained about the
> water droplets creating a prism. But he wanted to know why it forms an
> arch as opposed to, say, a multi-colored sheet.

The angle between the sun, the drops and you is what makes the rainbow
visible -- that narrow set of angles forms the bands in a circular
fashion. Think about staring at this point (in space):

X

Call it the "rainbow center" (it wouldn't be visible, of course, with a
real rainbow). The sun is behind you. For a given angle between
sun/drop/you, the angle that displays a certain hue describes a circle
around that "center", so you see an arc of that circle (interrupted by a
mountain or the trees or the horizon or the city skyline).

> For myself, I still don't quite get the prism deal. Each individual
> droplet isn't acting as a prism, otherwise you'd get thousands of tiny
> rainbows that wouldn't really be visible from a distance. Instead, a
> whole big group of them are banding together to create a giant prism
> visible from miles away. How do they get organized to do this?

Only one color is percrived as refracted/reflected/refracted from each
drop. The color depends on the angular position of the sun, the drop
and your eye. FIXED PITCH FONT PLEASE:

red orange yellow green blue violet
red orange yellow green blue violet
red orange yellow green blue violet
red orange yellow green blue violet
red orange yellow green blue violet
red orange yellow green blue violet
red orange yellow green blue violet X

And so on.

--
Blinky RLU 297263
Killing all posts from Google Groups
The Usenet Improvement Project: http://blinkynet.net/comp/uip5.html
Coming Soon: Filtering rules specific to various real news clients

Veronique

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Jun 6, 2006, 1:32:34 AM6/6/06

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Opus the Penguin wrote:
> The boy wanted to know what makes a rainbow. I explained about the
> water droplets creating a prism. But he wanted to know why it forms an
> arch as opposed to, say, a multi-colored sheet.
>
> For myself, I still don't quite get the prism deal. Each individual
> droplet isn't acting as a prism, otherwise you'd get thousands of tiny
> rainbows that wouldn't really be visible from a distance. Instead, a
> whole big group of them are banding together to create a giant prism
> visible from miles away. How do they get organized to do this?

I know a rainbow is curved in part because of the wavelength of the
different colors of light. Ergo, red (longest visible light) is always
on the outer part of the curve, and violet (shortest visible light) on
the inner.

V.
--
Veronique Chez Sheep

Erich

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Jun 6, 2006, 2:05:52 AM6/6/06

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In article <OX7hg.3625$PY6.1502@trnddc05>,
Tim Wright <tlwri...@verizon.net> wrote:

> Opus the Penguin wrote:
> > The boy wanted to know what makes a rainbow. I explained about the
> > water droplets creating a prism. But he wanted to know why it forms an
> > arch as opposed to, say, a multi-colored sheet.
> >
> > For myself, I still don't quite get the prism deal. Each individual
> > droplet isn't acting as a prism, otherwise you'd get thousands of tiny
> > rainbows that wouldn't really be visible from a distance. Instead, a
> > whole big group of them are banding together to create a giant prism
> > visible from miles away. How do they get organized to do this?
> >
>
> This explains it far better than I could.
> http://science.howstuffworks.com/rainbow.htm

Rainbows are only a starting point.

For explanations and photographs of just about every atmospheric optical
effect, you need to go here:

<http://www.atoptics.co.uk/>

... Erich

Mr C

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Jun 6, 2006, 2:54:35 AM6/6/06

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Not a "curve", it's a circle, most of which is below the horizon for
someone on the ground. At high altitude, like a plane, you can
sometimes see the whole thing.

Mr C

John Hatpin

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Jun 6, 2006, 4:16:52 AM6/6/06

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Out of interest, has anyone put an aerial photo of a full rainbow up
on the web? I've only seen pics of arcs.
--
John Hatpin

Greg Goss

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Jun 6, 2006, 4:29:41 AM6/6/06

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Opus the Penguin <opusthepen...@gmail.com> wrote:

>The boy wanted to know what makes a rainbow. I explained about the
>water droplets creating a prism. But he wanted to know why it forms an
>arch as opposed to, say, a multi-colored sheet.
>
>For myself, I still don't quite get the prism deal. Each individual
>droplet isn't acting as a prism, otherwise you'd get thousands of tiny
>rainbows that wouldn't really be visible from a distance. Instead, a
>whole big group of them are banding together to create a giant prism
>visible from miles away. How do they get organized to do this?

The center of the circle is the light source. You can see this by
playing with a garden hose, spraying it with your thumb on a sunny
day.

When the sun hits a raindrop, each colour gets bent a different
amount. The sun comes from behind you, hits a raindrop, bounces and
some of the light comes back at you. The red gets bent a different
amount than the blue light in a given drop.

When you are looking at the blue part, droplets along that line are
exactly X degrees from the sun behind you. That X is how far the blue
light gets bent. The red light from those particular droplets get
sent off at angle Y which doesn't reach your eyes. When you are
looking at the red part, all the droplets along that line form a Y
degree angle between you and the sun. Y is the amount that red light
gets bent. The light of other colours goes off in other angles.

When the light scatters off the droplet, each colour heads off in a
particular direction. Because the sun can be considered infinitely
far away, all of the droplets in a given line from your eye form the
SAME angle between that line to your eye and the line to the sun. If
that angle is the angle that a particular colour bounces, then all of
those drops bend the same colour the same amount. Along a different
line, the drops form a different angle between the lines to your eye
and to the sun. That angle would have a differnet colour.

Each droplet spews out ALL the colours in different directions. The
particular spew towards your eye is controlled by the angle between
the sun and your eye. And all the drops along that line have the same
angle, and therefore the same colour.
--
Tomorrow is today already.
Greg Goss, 1989-01-27

Tim Wright

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Jun 6, 2006, 9:47:50 AM6/6/06

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Here's one that's sort of what you're looking for.
http://antwrp.gsfc.nasa.gov/apod/ap040806.html

Mr C

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Jun 6, 2006, 9:53:30 AM6/6/06

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Here's another:
http://www.dlcphotography.net/CR2/1D2_00937.htm

Mr C

ra...@westnet.poe.com

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Jun 6, 2006, 10:26:00 AM6/6/06

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Opus the Penguin <opusthepen...@gmail.com> wrote:

> The boy wanted to know what makes a rainbow.

Heh, we have a little kids book with colored ribbons where the baby bunny
goes about asking all the animals what makes a rainbow and each animal
touts thier color as they show off thier bit of colored body: "'Orange'
replied the fox, swishing his orange tail, 'you need orange to make a
rainbow'" to which I affixed the folloing post-it on the penultimate page:

"Mr. Physiscist?" asked the baby bunny, "What makes a rainbow"
"Diffraction" replied the physicist, closing his CRC handbook, "You need
differential diffraction of light through water drops to make a rainbow."

> I explained about the
> water droplets creating a prism. But he wanted to know why it forms an
> arch as opposed to, say, a multi-colored sheet.

That's geometry: the water drops are spherical, and so the angle from a
drop between the lightsource and the observer for a given color traces
out an arc for the observer. That is, red is all drops that form a 11
degree angle (number made up) between the sun and the eye, yellow is at
11.1 and violet is at 11.2 or so, and that makes an arc.

> For myself, I still don't quite get the prism deal. Each individual
> droplet isn't acting as a prism, otherwise you'd get thousands of tiny
> rainbows that wouldn't really be visible from a distance.

No, you get exactly that: no two people are seeing the same rainbow, heck,
each eye isn't seeing the same rainbow. Different drops are doing the job
for each viewer.

> Instead, a
> whole big group of them are banding together to create a giant prism
> visible from miles away. How do they get organized to do this?

No organization: they just have to be the drops in the right place to
create the right sun-drop-eye angle for a given color.

John - OK, actually, it's the angles painting and erasing furiously.
--
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Mean People Suck - It takes two deviations to get cool.
Ask me about joining the NRA.