Answer 1:
This is a cool question and not easy to explain
in an email, because I need to include a photo to
explain my answer.
In order to see a rainbow we need rain,
sunshine and an observer who has his/her back to
the sun.
When white sunlight strikes a falling drop of water at a relatively low angle, the raindrop in the air acts like a prism and the light is broken into a spectrum of red, yellow, green, blue, violet. When the light enters the raindrop, it bends (it refracts) differently depending on their wavelength.
The violet light bends at a rather
sharp angle, the red light is bent the least. The
light continues into the drop and is reflected
from the back of the drop to the front. When the
beam hits the front it is refracted again and
emerges from the drop as the color spectrum that
we see in a rainbow.
Now, what we see as observers depends very much
on where we are standing: Please look at the
picture at the web site (which is also where I got
my answer from): click here
This picture explains how we see the colors
red and violet; the other rainbow colors are not
shown to keep the picture simple.
When the light hits raindrop A only the red light is visible to the observer. We see the red light, because it is directed towards the
observer's eyes. The violet light is directed
above the level of the eyes and so are all the
other colors, that is why we do not see them.
However, in the lower drop (raindrop B the red light is directed below the eye level and this
time the violet light is visible to the observer.
This means that we see only one color from each
raindrop at a certain height. In the raindrop A we see only the red light, all other colors will exit at a lower angle and therefore be above the
observers eyes.
The sunlight will hit all the surrounding raindrops in the same way, so they will all bounce red light onto the observer and we will see a band of red. Raindrop B is much lower in the sky, so it doesn't bounce red light to the observer. At its height, the violet light exits at the correct angle to travel to the observer's eye. All the drops surrounding raindrop B bounce light in the same way. The raindrops in between A and B all bounce different colors of light to the observer, so the observer sees the full color spectrum.
This explains how we see the colors of the
rainbow and you now also understand that the way we see the rainbow (faint or strong) depends on where we are standing.
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