Most Australian capital cities have more than 200 sunny days a year with clear, blue skies.
But do you know why the sky is blue?
It’s all to do with light and how we see it.
Light is made up of a range of colours, called a spectrum*. A rainbow shows you some of that spectrum: red, orange, yellow, green, blue, indigo and violet all lined up across the sky when there is rain around.
There are more types of light, but those that appear in the rainbow are the ones we can see.
Other types of light that we can’t see are ultraviolet light (which causes sunburn), microwave (also used in microwave ovens to cook food) and radio (that we can send music or other sounds on).
Light is a type of energy and that energy moves in waves. Blue light moves in short waves. Red light moves in longer waves. When the sun shines through the Earth’s atmosphere to reach us, the blue part of the sunlight gets scattered by all the tiny molecules* of moisture, different gases and anything else in our atmosphere. This scattering is called Rayleigh scattering, named after a famous UK physicist* Lord Rayleigh.
The red light comes straight through the atmosphere without being scattered, so we can’t usually see it.
It could help to imagine an arrow that is a really wriggly line (blue light, with short, close-together waves) and another arrow that is much straighter (red light, with much longer, spread-out wavy shapes to it). We all know that the straighter the arrow, the straighter it will move through the air.
At sunrise and sunset, the sun appears quite red, because the light is moving towards us closer to the ground, where the atmosphere* is thicker with moisture, dust and other particles*. The bluer light is scattered so much it’s scattered away from our line of sight and it’s mostly red light left for us to see.
The sun looks whiter when it’s high overhead because there’s less for the blue light to hit to be scattered.
REMEMBERING RAINBOW COLOURS
Can you remember the colours of a rainbow in order? It helps some people to remember the initials of the colours as a made-up person’s name: Roy G Biv, for Red, Orange, Yellow, Green, Blue, Indigo and Violet.
Other people remember the colours in the opposite order: VIBGYOR.
Roy G Biv is a type of mnemonic. Mnemonics are systems of remembering a pattern of letters, words or ideas. You can use mnemonics other people have thought of to remember things, or make up your own. Do you know any mnemonics?
- spectrum: a wide range
- molecules: tiny particle, made up of a group of atoms stuck together
- physicist: scientist who studies energy, such as light, heat, sound and magnetism
- atmosphere: the area of gases around a planet, including Earth
- particles: a tiny piece of matter, such as dust
LISTEN TO THIS STORY
- How many colours can you see in a rainbow?
- What are the types of light mentioned we can’t see?
- How does light energy move? What shape?
- Who was Lord Rayleigh and why is he mentioned?
- Why does the sun sometimes look red at sunset or sunrise?
1. Noon and sunset skies
Draw 2 pictures:
- The sky in the middle of the day
- The sky at sunset
Write a paragraph to go with each drawing explaining why the sky is that colour at that particular time of day. Add any extra items to your drawing (such as wavy arrows) that you think are needed to help with your explanation.
Can you find out the answer to any of these similar questions?
- Why is grass green?
- If water is clear, why does the ocean look blue?
- What are clouds made out of?
- Where does the moon’s light come from?
Time: Allow 30 minutes
Curriculum links: English, Science
With a partner see if you can you identify all the doing words/verbs in this text. Highlight them in yellow and then make a list of them all down your page. Now see if you and your partner can come up with a synonym for the chosen verb. Make sure it still makes sense in the context it was taken from.
Try to replace some of the original verbs with your synonyms and discuss if any are better and why.
HAVE YOUR SAY: What other science questions do you think Kids News should answer? If you use mnemonics for remembering things, you could share those here too. Use full sentences. No one-word answers.