Rainbows

Hello Guest Kris,

The physics of rainbows is quite complex, with the light beam being internally reflected in each minute water droplet, a number of internal bounces, and the rainbow becomes visible.

The arc is such, because what you see is the shape of the light source = the sun.

The height of the rainbow is relative to the zenith (highest point of the sun in the sky) of the sun.

At local zenith normally noon - the rainbow has the highest possible arc.

At sunset, the arc of the rainbow is at the nadir = lowest point, and the result is a very low, "shallow" arc made by a rainbow at this time.

There are circular rainbows, which may be seen when looking down into the spray of a waterfall, with the sun immediately behind the person - This is called the "Glory".

Have a look at this interesting Webpage: http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=44

Note you will need to have "Java Runtime installed, to obtain the full benefit of the above weblink.

Java Runtime may be freely obtained from that webpage, via the Download link.

Kind Regards....

"The arc is such, because what you see is the shape of the light source = the sun."

No - because the light is incident on our eyes, i.e. we are a 'point observer', analogous to a point source; we are 'collecting' the rainbow which exists for any observer in the field in which it occurs.

More here: http://en.wikipedia.org/wiki/Rainbow

Note the remark concerning complete rainbows/circles observed from aircraft.

It has nothing to do with the shape of the sun (To put if another way: if the sun were square, you wouldn't see square rainbows )

RF_G

Yes, I have also seen full circle rainbow many times from the aircraft. Also I have seen full circle rainbow in moon light, in rainy season.

Another aspect of rainbow: We can feel rainbow touching to ground at some specific locations, just few kms away. The distance of these points from our observation point depend up on the sectorial size of the rainbow, which in turn depends upon the latitude of the Sun.

I have seen rainbow with its arch balanced on top of clouds during journey from Srinagar to Delhi. This incident changed my thoughts that the rainbow formed at height in the sky should be a circle, and on ground, only the bottom half is visible due to spherecal shape of the earth.

My another observation is that only the rarified particles of water can cause a rainbow. The dense fog at a distance and the sun behind me has never presented a rainbow.

And what shape is the sun from where you are, Sparky? I don't think that's really why. I think it has more to do with the fact that all points on a rainbow are the same apparent distance from the observer, and the only shape that can satisfy that is a circle, or at least an arc representing a segment of one.

Or else it's the weight of the pots of gold at the ends holding them down...

Light is always reflected by water droplets but at about 42 deg the light separates into the colour bands.

You will therefore see the primary rainbow only at that arc where the reflection angle is about 42deg against the "parallel" rays from the sun.

Because Raindrops are round:)

Thanks god (?), Su is not cubical.... rectangular nor the water drops.

Hello Kris, The round droplets of water separate the the sun light into it's color spectrum just like a prism makes lines then the light shines through it . The water drop is round that why the rain bow is circular . If your perspective is on the ground you will for most of the time only see an arch. Like some have said if your perspective is above the mist then you will see the whole circle.

You could find a round clear glass marble and let the light shine through it you would see the rain bow colors in a circle.

the color spectrum is bent by the color wave length blue=short, red= long.

Like when the sun light shines through the atmosphere the water vapor scatters the shorter blue thats what makes the sky blue if its clear. Same as the sun sets the light path is longer so the light travels further through the atmosphere to give the red sun sets. Dirt,dust, and other impurities in the atmosphere can change what you see to some extent.

Hope this clears up some of the others colorful post for you.

metalSmith's

When flying in an aircraft in the proximity of rain drops with the sun at the back one can see the rain arc. (full circle)

Whether it is a true arc is questionable because a rain drop gets deformed while falling. It is not symmetrical from top to bottom and may separate the colours at a different angle.