Rainbows and Ice Halos
What do most people think when they see a rainbow - awww pretty?
But what is it that forms the colours in a rainbow?
The rainbow is made up of several colours: Red, Orange, Yellow, Green, Blue, Indigo, Violet
The colours of the rainbow occur from 2 facts:
- Sunlight is made up of the range of colours that the eye can detect. The variety of sunlight colours when combined looks white to the eye.
- Light of different colours is refracted by different amounts when it passes form one means to another.
Why is the sky brighter inside a rainbow?
Have you ever noticed the difference between the sky outside the rainbow to the sky inside the arc? This is due to the fact that there is more light inside the rainbow arc; because this light is a mix of all the rainbow colours.
How are rainbows formed?
Have you ever noticed that you can only see rainbows when the sun is directly behind you and it's raining in front of you? Rainbows form when the sunlight shines through millions of raindrops. Sunlight is a mixture of colours; when it passes through a raindrop it is refracted and the light splits into the seven colours.
Why is a rainbow an arc shape?
We see rainbows in the shape of an arc, however rainbows are formed as a circle. The light from the sun is refracted by the raindrops. This angle is so big it is centered directly opposite the sun. This is called the 'antsolar point.' The arc is part of a circle of light that is cut off by the earth. It is possible to see a full rainbow, but only from a certain height such as from an airplane.
Ice Halos
Tiny ice crystals in the atmosphere forms halos by reflecting and refracting light.
Halos appear in the skies more frequently that rainbows do, they can be seen on average twice a week. There are different frequent halos to be seen:
Circumzenithal arc
The circumzenthial arc is the most beautiful of all halos; it is often known as an upside down rainbow. This halo is never a complete circle, and exceptionally rare.
22° Circular Halo
The 22° radius halos are visible all over the world and throughout the year. Look out for them especially when clouds are fine and you can almost see through them. These clouds are cold and contain ice crystals even in the hottest climates.
Much smaller coloured rings around the sun or moon are known as the corona which are produced by water droplets.
A corona can be seen when the sun is partially covered, look for one around the moon when it is nearly full and the sky is dark.
