Can I Reach the End of a Rainbow with a Shovel?

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Discussion Overview

The discussion revolves around the nature of rainbows, including their formation, visibility, and the conditions required to observe them. Participants explore various aspects of rainbows, such as their size, the possibility of creating them at night, and the effects of water droplet size and direction on their appearance.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants inquire about the smallest possible rainbow arc that can be viewed, suggesting it may be close to the size of a water droplet.
  • There is a proposal that creating a rainbow at night with a sprinkler and a torch is feasible, contingent on the brightness of the torch.
  • Participants discuss whether minute drops of water can produce rainbows, with some affirming that mist can indeed create "mistbows."
  • There is uncertainty about whether water droplets need to be traveling in a consistent direction and speed to form a rainbow.
  • Factors affecting the saturation and definition of rainbow colors are debated, with suggestions that background conditions and the number of water droplets play a role.
  • Some participants argue that one cannot be "above" a rainbow, as it is not a physical object, while others share personal experiences of seeing rainbows from planes.
  • There is a whimsical discussion about the impossibility of reaching the end of a rainbow, with some participants sharing anecdotes about being in mist and observing rainbows at close distances.
  • Questions arise regarding the relationship between the viewer's distance and the extent of the rainbow, with some suggesting that the radius is proportional to this distance.

Areas of Agreement / Disagreement

Participants express differing views on the nature of rainbows, particularly regarding visibility from different positions and the conditions necessary for their formation. There is no consensus on several points, including the feasibility of reaching the end of a rainbow.

Contextual Notes

Some claims depend on specific definitions and assumptions about the nature of light, water droplets, and the observer's position. The discussion includes various interpretations of personal experiences and theoretical considerations.

Tristanthompson
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I'm interested in rainbows.

I'm talking about good old fashioned arc/halo rainbows like those you see in the sky.
  1. Sometimes you see rainbows from lawn sprinklers. How small would the smallest rainbow arc conceivably possible to view be?
  2. Could I make a rainbow at night using a sprinkler with a torch?
  3. If so, how bright would my torch light need to be?
  4. Will even minute drops of water i.e. mist produce rainbows? Mistbows?
  5. Do the water droplets have to be traveling in a consistent direction at a consistent speed?
  6. What factors make the colours in rainbows more saturated and the bands more defined?
  7. Can you be above a rainbow and look down on it without it losing its form?
I hope you can help!

Thanks,

T
 
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A lot of questions there.
I can tell you the answer to the last one from personal experience.
If you are in a plane, it is possible to see a whole rainbow, the full circle, it's characteristics are the same as a half rainbow which can be seen from the ground.
 
Tristanthompson said:
I'm interested in rainbows.

I'm talking about good old fashioned arc/halo rainbows like those you see in the sky.
  1. Sometimes you see rainbows from lawn sprinklers. How small would the smallest rainbow arc conceivably possible to view be?
  2. Could I make a rainbow at night using a sprinkler with a torch?
  3. If so, how bright would my torch light need to be?
  4. Will even minute drops of water i.e. mist produce rainbows? Mistbows?
  5. Do the water droplets have to be traveling in a consistent direction at a consistent speed?
  6. What factors make the colours in rainbows more saturated and the bands more defined?
  7. Can you be above a rainbow and look down on it without it losing its form?
1. I'd guess somewhere close to the size of a water droplet, but that's mostly just a guess.
2. I believe so. I think the key would be to make sure you're viewing from the right angle, which I think is 42 degrees from the light source.
3. Offhand I'd say the brighter the better.
4. They will indeed: http://en.wikipedia.org/wiki/Fog_bow
5. I don't think so, but you may get interesting effects if they are moving around in certain manners: http://en.wikipedia.org/wiki/Rainbow#Twinned_rainbow
6. Not sure.
7. No, because a rainbow is not a physical object, so you cannot be 'above' it. In order to see the rainbow you have to be looking towards water droplets at a specific angle from the light source. Any other angle and you won't see a rainbow.
 
6. The saturation of the bands will depend a lot on the background. You see the sum of light going from a particular direction so a dark cloud behind where the bow appears to come from will make it more 'vivid'. I guess you could arrange an artificial form of rainbow with a black background (possibly a cave mouth). The problem is that the bow is formed of sunlight coming over your shoulder and that light will illuminate the background as well.
My opinion is that we are so stunned by the effect of a rainbow that we forget to notice just how desaturated the colours are. Do the old eye-dropper test in Photoshop (other packages are available) and look at the RGB values in your very best photo of a rainbow and notice that there is very little difference between the three. We look with our hearts and not ur heads, I think.

The colours you get from the interference off oil films on water can be much more saturated. It's not the same phenomenon, of course and the interference effect will give you 'notches' in the spectrum, rather than peaks. So, more light in the first place and the background can be very dark.
 
1. Sometimes you see rainbows from lawn sprinklers. How small would the smallest rainbow arc conceivably possible to view be?

The colours of a rainbow are formed by the refraction of light which can be done by a very small prism. You could make a straight one too small to see. However if you want to see a proper arc shaped rainbow then you need to look at how the arc shape is formed..

https://plus.maths.org/content/rainbows

The size depends on the refractive index of the droplets not their size.

2.Could I make a rainbow at night using a sprinkler with a torch?

I don't see why not.

3.If so, how bright would my torch light need to be?

How bright can your eyes see?
4.Will even minute drops of water i.e. mist produce rainbows? Mistbows?

Yes.
5.Do the water droplets have to be traveling in a consistent direction at a consistent speed?

No.
6.What factors make the colours in rainbows more saturated and the bands more defined?

I believe it makes a difference how many water drops there are per cubic meter.

7.Can you be above a rainbow and look down on it without it losing its form?
Not normally. What matters is the relative position of you and the light source. Due to the way a rainbow is created it forms on the opposite side of you to the sun. eg if the sun is to the west of you the rainbow will be to the east. Change the position of you or the sun and the position of the rainbow will move. You can sometimes see a rainbow below you if you are in an aeroplane but it's not the same one that someone on the ground might be seeing. Everyone sees a rainbow in a slightly different place because their and their eyes are in a different place.
 
As a slightly whimsical answer, there's a reason why we still don't have that pot of gold; it's just impossible to be at the end (or on top) of a rainbow :)
 
rumborak said:
As a slightly whimsical answer, there's a reason why we still don't have that pot of gold; it's just impossible to be at the end (or on top) of a rainbow :)
It actually isn't.

I have stood in a volume of mist and the rainbow was effectively at zero distance.
I have also flown in a plane and looked down upon a rainbow.
 
DaveC426913 said:
I have stood in a volume of mist and the rainbow was effectively at zero distance.

Unless I am mistaken, the radius of the rainbow is proportional to the viewer's distance to it, no? Meaning, when you stand right in front of the mist, its extent is 0.

I have also flown in a plane and looked down upon a rainbow.

I think this one just comes down to how one defines "on top" :smile:
 
rumborak said:
Unless I am mistaken, the radius of the rainbow is proportional to the viewer's distance to it, no? Meaning, when you stand right in front of the mist, its extent is 0.
Well, it's extent is zero if its distance is zero - i.e. at my eyeball. But how close does one need to be to 'be' somewhere, such as a the end of a rainbow, or to assess whether there is a pot of gold there? Six feet?
 
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DaveC426913 said:
Well, it's extent is zero if its distance is zero - i.e. at my eyeball. But how close does one need to be to 'be' somewhere, such as a the end of a rainbow, or to assess whether there is a pot of gold there? Six feet?
The "Engineer's" answer to this would be that, if you started to use a spade and went to reach into the hole you had dug, the 'end' of the rainbow would move away from you. So, close but no cigar (gold). :frown:
 
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