How are rainbows formed ?
The rainbow is a natural
spectrum. It can only be sighted when you are facing away from the sun. Furthermore, the
sky behind the rainbow must be hazy or cloudy. It is these conditions that make seeing a
rainbow possible. But just what is behind this occuring that we can see the 7 colours ?
The haze or clouds consists of
many water droplets. Each drop of water acts as a prism breaking the sunlight into its
component colours. Each single drop reflects only 1 colour directly to our eyes, depending
on the height of the drop above the horizon.
There is also a weaker rainbow
known as the secondary bow outside the bright main bow. This is formed when light is
reflected twice within the rainbow before emerging. The second reflection has the effect
of reversing the order of the colours. Red will thus appear at the inner edge of the
secondary bow, while white will appear at the outisde of the main bow. Refer to the
diagrams below for understanding.
Why is the sky blue ?
Around the earth, the air
comprises of many tiny particles including dust and water vapour. In daytime, the sunlight
passes through the air, the blue waves are reflected by the particles while the other
waves are unaffected. The reflected blue rays goes into our eyes and thus the sky appears
blue.
At sunset, when the sun is low
down on the horizon, the blue light is reflected away from our eyes. Thus, we see the
light that remains, and the sky will appear red.
Why do mirages occur ?
A mirage is
actually a distant object appearing above the ground when it it seen. The warm air above
the ground is the key to mirages. The light rays travel directly up from an object to your
eyes and also down directly towards the ground for the warm air to refract it back to your
eyes by the warm air. You will then see yourself an inverted image under the image.
