RAINBOWS - A SYMBOL OF HOPE

Rainbows are considered one of nature's special gifts and a symbol of hope. They have inspired painters, writers and songwriters, and most people can't resist capturing a rainbow in a photograph be it on a sophisticated camera or a phone. In reality, this magical phenomenon is simply an optical illusion which occurs when light from the sun is scattered by water droplets, by a process of refraction. Each water droplet has a role to play in the formation of the rainbow.

How is a rainbow formed?

Sunlight is made up of light of many different wavelengths or colours which travel at different speeds. When sunlight enters a water droplet at a specific angle, white light is separated into different colours, each of which is reflected and refracted at a particular angle. The angle is a fixed measurement of between 40 and 42 degrees between the eye and the sun. The colour refracted depends on the angle at which the sunlight strikes the back of the water droplet. White light enters one individual rain droplet and exits as one specific colour of the spectrum. Each water or rain droplet reflects all colours at some time, but only one colour at a time comes back to the eye. We see the colour spectrum of the rainbow as the light passes through the raindrop at different angles.

The position of the sun and the raindrops in relation to the viewer need to be just right for a rainbow to be seen. The water source must be in front of the viewer. The sun needs to be behind the viewer, low in the sky, at an angle of less than 42 degrees above the horizon. The lower the sun is in the sky, the more of an arc of the rainbow will be seen.

Are all rainbows shaped like an arch?

A rainbow forms a full circle but appears to be semi-circular because we can only see the light reflected by the rainbow above the horizon. However, if you stand with your back to the sun and turn on the garden hose, you can create a perfectly circular rainbow in the fine spray of the water.

Are there really seven colours in a rainbow?

Children are taught that there are seven colours in a rainbow – red, orange, yellow, green, blue, indigo and violet, an order which never changes. These are the colours of the visible spectrum. Rainbows contain over a million hues, but they are not all visible to the human eye.

Does everyone see the same rainbow?

No two people see the rainbow in exactly the same way. Since it all depends on how the light is being bent and reflected back to you, everyone sees something different. When you're looking at a rainbow, you are looking at light that's reflected by raindrops above the horizon. But your horizon is always slightly different from everyone else's, so you can never see the same rainbow as someone else.

Do rainbows only appear with rain?

For a rainbow to be formed, there need to be water droplets in the air and light has to shine through those droplets at just the right angle. Water droplets can be in the air for many reasons other than rain, for example when its misty or when there is spray from the sea crashing against the rocks, or even with dew. No matter what the source of the water droplets in the air, though, the sun has to be at the proper angle and behind your back.

Can you make a rainbow disappear?

Rainbows are highly polarised objects, which means their light waves are vibrating in one plane – in this case, a vertical one. Polarised sunglasses are also polarised vertically because they need to block reflections and glare. Horizontal light waves, for example off pools of water, can't get through vertical polarisers. If you turn your vertically polarised sunglasses sideways, effectively creating a horizontally polarised pair of sunglasses, the rainbow's light waves will be blocked, causing the rainbow to magically disappear.

Do rainbows appear only during the day?

If water and sunlight are the ingredients needed for a rainbow, it makes sense that they appear only during the day. However, it is possible for a rainbow, known as a moonbow or lunar rainbow, to occur at night. These are created when light reflected by the moon hits water droplets in the air. Because moonlight is not as bright as sunlight, they are fainter than rainbows, but contain the same seven colours. The human eye is unable to perceive colours in dim light, so we see moonbows as white.

Is a rainbow always single?

Double, tertiary (triple) and quaternary (quadruple) rainbows can all occur, but anything more than a double rainbow is difficult to see. Multiple rainbows occur when light is reflected twice, three times or more inside water droplets. When this happens, the second or third rainbow appears above the main one and is fainter. Its colours are reversed with red on the inside and violet on the outer arch.

Is there a pot of gold at the end of a rainbow?

Is this age-old myth about rainbows the one which makes us see rainbows as a symbol of hope? Sadly, because a rainbow is a circle and therefore has no end, we will never find the answer to this question. Or the pot of gold!