how do rainbows stay for so long if the rain had stopped and more importantly how do they happen if the drop fall
In: Chemistry
They persist only when there is sunlight at the correct angle hitting raindrops in the distance where it’s still raining.
Rainbows are ony visible if there is rain. But it doesn’t have to be raining where you are, only where the rainbow forms, and that can be some distance away. After all, there has to be sunlight, so it stands to reason that rainbows happen when there are rainclouds moving over the landscape, interspersed with sun and blue sky.
The sun must be behind you at an approx. 30 degree angle for it to form a rainbow in rain some distance away from you in the opposite direction. It is the millions of raindrops that are at the exact right position above the ground at any given moment, as the rain falls, that contribute to the scattering of light ) (by internal refraction in the drops) of the rainbow in your direction. So it is that as raindrops fall too low they stop contributing to the rainbow light in your direction, while new raindrops fall from above and move into the correct position to be part of the rainbow light in your direction.
I emphasize *your direction* because all raindrops that are illuminated by the sunlight will scatter light in a rainbow kind of way, but those that are in other positions than where you see a rainbow, will not form a rainbow that is visible for you, in your position. But if you could move fast around, you would notice that the rainbow would “follow you” around, keeping the same angle with the sun. Which is why you cannot really find that pot of gold at the end of one…
It’s not raining where you are, but it’s still raining in the direction where you see the rainbow. It always needs raindrops to keep refracting the sun’s light.
Also, remember that there’s more than one raindrop there. You have countless raindrops, all falling at different times. You won’t see a rainbow from just one raindrop. At best, you’d see a colourful flash, so long as you happen to be at the right angle. But, when you have a million raindrops, each refracting the light from a different direction, it will all combine into the rainbow that you see.
Rainbows are cones.
Like an old-fashioned megaphone – a cone with you (or your eyes) at the point of it, with the centre-line of the cone extending back through your head to the Sun.
When you see a rainbow you are seeing light from the Sun being bounced off water droplets (from rain or something else) in that cone. So even if you see a complete “bow”, different parts of that bow may be miles away from each other, some far closer than others.
As for why we get them even if the drops fall, it is kind of like how computer or TV screens work; even though they are made up of lots of tiny pixels, our eyes cannot tell apart the different pixels (unless we look really close) so we see a single continuous image.
With rainbows we are seeing a “pixel” of colour from each water droplet, and the whole bow is made up of lots of these dots of light from many, many water droplets – but because our eyes cannot tell one droplet from the next they blur into one.
Sure, the droplets are falling, but that doesn’t matter as there will always be another droplet right behind it – kind of like how we can see waterfalls; each individual bit of water is moving but there is another bit of water right behind it, taking its place.
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