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Asked by 492spea43 to Francesca, Laura, Matthew, Andrew, Rebecca on 18 Nov 2014. This question was also asked by Ms. Scientist.
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Matthew Camilleri answered on 18 Nov 2014:
The rainbow is an arch of colours visible in the sky, caused by the refraction and dispersion of the sun’s light by rain or other water droplets in the atmosphere.
This phenomenon can also be observed under a number of different shapes, including a very rare whole circle, which only occurs rarely but is very beautiful to see.
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Andrew McKinley answered on 18 Nov 2014:
A rainbow is probably the most beautiful display of atmospheric optics, and it happens as sunlight hits a raindrop. You will (hopefully) have seen sunlight passing through a prism, and seeing the spectrum of colour as the white light splits up into its component parts. This happens because as light enters a different material it changes direction – blue light changes direction more than red light, so white light ‘disperses’ in this way. A rain drop does the same thing.
The question is, why does it form an arch? Well, next time you see a rainbow, make some observations: Where is the rainbow? Where is the sun? If you look at the rainbow, where is the shadow of your head?
If you are very lucky and you can see the whole arch, you will see it is a segment of a circle, touching the ground to your left and to your right. Where is the sun? Hopefully you’ll notice it is directly behind you. Finally where is the shadow of your head? You should notice that the shadow of your head is *exactly* at the point which would be the ‘centre’ of the arch – if you had a compass, and put the pin where the shadow of your head was, you could trace the whole arch of the rainbow, and then even connect the two ends. This tells us that the rainbow is uniquely yours! Only you can see that rainbow – other people will see *a* rainbow, but it will be in a slightly different place, depending on the position of the shadow of their head!
If you draw a line from your head’s shadow to your head, and then take that line out to the rainbow, you could measure the angle – and this angle would *always* be between 40 (blue band) and 42 º (red band) – this is known as the “Rainbow” angle, and is the result of the light rays reflecting once as they pass through the raindrop. Every point where you can make this angle, and there are water droplets, you will see the colours of light. If you can get high enough – from a mountain, or from a plane, you will see a completely circular rainbow, and they are absolutely amazing!
Sometimes you see a secondary arch as well – this is always between 50 and 53 º – but the colours are reversed. This secondary arch will be less intense, and is the result of a “double reflection” as the light passes through the raindrop – it is however less intense because not as much light goes through two reflections inside the drop…
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Laura Schofield answered on 18 Nov 2014:
I think Andrew is the most qualified to answer this and has given an excellent explanation there! The only thing I can really add to that is that the different colours are refracted (or bent) to different degrees because of their wavelength. Red light has a much longer wavelength than blue light and shorter wavelengths are much easier to refract. That’s why the blue is always on the inside and red is always on the outside, because the blue light has been refracted the most and red light has been refracted the least.
Comments
492spea43 commented on :
thank you for answering my question as i always have wanted to know what is a rainbow.