4

Rainbow forms when light rays pass through a raindrop (usually, it can be a watet droplet also) and it undergoes several phenomenon like refraction , reflection , dispersion , But after the rainbow is formed it should not stay for much long as the rain drops are falling downwards so their position must change . And the rainbow should disappear .But this doesn't happens in reality . Why is it so ? The actual shape of raindrops is like this.

Chloritone_360
  • 241
  • 1
  • 3
  • 14
  • 1
    Imagine looking at yourself in a mirror while the mirror is slowly moving downward. Is your image in the mirror going to move downward too? – march Aug 28 '15 at 05:22
  • No but then only the lower part of my body will be visible not my whole body . Same should also happen with the rainbow. – Chloritone_360 Aug 28 '15 at 05:24
  • But (probably) rain never just stops. Rather, it ebbs. Therefore, what I would expect is that you always see a rainbow, but it will slowly fade as the density of rain falling decreases. If it were the case that the rain just suddenly stopped, you would exactly see the rainbow disappear from the top down (which is what you see if you ever see a rainbow in the water of a sprinkler that suddenly turns off. – march Aug 28 '15 at 05:28
  • But still it is not continuous .Rain falls discontinuously. – Chloritone_360 Aug 28 '15 at 05:30
  • Rain drops fall as aerosols (tiny, dust like water particles), and even though they are single objects, the amount and size of them makes it seem as a continuous fall. The mirror analogy from @march seems very good, just imagine a very, very large mirror. So large that your image is not close to the edge while it is lowered – Steeven May 14 '17 at 10:30
  • In fact, imagine it raining mirrors. Then your reflection would always be visible to you even if one mirror falls. (Please do not try this as an experiment; mirrors will break, you will be sad.) – Bob Knighton May 14 '17 at 11:01
  • Wow, interesting. Where I live it didn't use to rain with the sun in the sky. Instead, we used to see the rainbow AFTER the rain, and I had always been told that it's due to raindrops staying in roofs or any tall object. So is that wrong? – FGSUZ Sep 07 '17 at 00:28
  • @FGSUZ yes , it is wrong. see https://en.wikipedia.org/wiki/Rainbow#Explanation – anna v Sep 07 '17 at 03:53

1 Answers1

3

But after the rainbow is formed it should not stay for much long as the rain drops are falling downwards so their position must change .

As discussed in the comments, and explained in the wiki article , the raindrops replace each other as they are falling and your eyes see a continuity similar to the one when watching movies and television.

And the rainbow should disappear

If it were only raindrops that could form a rainbow, i.e drops of some milimeters, yes it should disappear. But also tiny droplets hovering after the main rain drops, create rainbows. See this over a water fountain, where the mist is enough on the left.

rainbow

After the rain, and depending on the weather conditions, mist can persist:

The persistence of water vapor in the air depends on updrafts of warm air. As warm air rises, it carries humidity that condenses into vapor droplets when it hits higher layers of colder air. Once condensed, the vapor tends to fall. But continuously rising warm air replenishes the fallen droplets, so the rainbow phenomenon persists as sunlight is refracted and reflected through new droplets that replace the old. When warm updrafts cease, so that no further humidity is carried upward to condense to droplets, the rainbow will dissipate and disappear.

anna v
  • 233,453
Ernie
  • 8,516
  • @annav : Thanks for the expansion. The photo nicely illustrates the rainbow persisting in rising mist, as well as falling rain. – Ernie Oct 08 '17 at 12:44