Graduate Resources

A picture containing drawing

Description automatically generated
or, Why the Sky is Blue!

Visible light is made up of all colours: red, orange, yellow, green, blue, violet, and everything in between. In space, light from the sun and stars would look almost white, as it contains all these colours. On the surface of the Earth, however, light has passed through the atmosphere, and the Sun appears very yellow. Let’s look at the reason why, and along the way we’ll explain why the sky appears blue, and why blue Christmas lights on your house don’t seem very bright from a distance.

The questions about blue light first arose when we were looking at how to demonstrate that white light is made up of different colours, using glow tubes.

We had previously noticed that the blue Christmas lights on our home, while nice and bright in the yard, were invisible from the road. The question we asked was ‘Why does blue light seem to fade out with distance, while red and yellow don’t?’

The answer has to do with air … the molecules that light must pass through to get to your eye. In order to explain what happens to the light, you’ll need to remember that ordinary white light contains all the colours of the spectrum.

A picture containing kite

Description automatically generated
The fact that white light is made up of all the colours of the rainbow was demonstrated by Isaac Newton using a prism. White light passed into the prism came out in a spectrum, because the glass caused the different colours to slow down by different amounts, changing their angles of exit. This phenomenon is called refraction.

As white light from the sun enters our atmosphere, it must pass through this gas, which is composed mostly of nitrogen and oxygen molecules, before it can reach the surface. As it passes through, each of the different colours in the light interact with the air molecules.

A simple way to describe what happens would be to say that the air molecules, which are about 0.0004 millimeters in diameter, are very close in size to the waves of blue light. Other colours have bigger or smaller waves, and mostly pass right through, but the blue light waves hit the air molecules and scatter in all directions. As the sunlight comes down through the atmosphere, the blue light in it gets scattered all over the place. Some of this scattered light (there’s a lot of it) reaches our eyes, making the sky seem blue. The sunlight that’s left that finally reaches the ground has lost most of its blue light, leaving it yellowish in colour, so the sun itself appears yellow.

In space, there is no air to scatter the different colours in light, so the sun would look white and the ‘sky’ would be black.

This also explains why blue lights get dimmer with distance. If you’re far enough away from the blue Christmas lights decorating your house, much of the blue light from them gets scattered every which way, and there wasn’t very much of it to start with, so very little of it gets to your eye. You can’t see the bulbs.

A more detailed explanation of the scattering phenomenon goes something like this. Molecules of air, in particular nitrogen and oxygen, are surrounded by the electron ‘clouds’ of their individual atoms. The outermost of these electron clouds can vibrate at a certain frequency, called the resonant vibration frequency. Any outside light energy hitting them will cause additional vibrations, and that light will then scatter off in a different direction. This is called Rayleigh scattering.
All light energy striking these molecules scatters a little bit in this way, but the energy of blue light more closely matches the resonant vibration pattern of the molecules themselves, so more of it is used to vibrate the electron clouds, and more of it gets scattered. Thus when white light hits air molecules, more of the blue light in it is scattered to the side than the other colours.


Incidentally, the energy in ultraviolet light exactly matches the resonance frequency of nitrogen and oxygen molecules. As a result, almost all of the energy from ultraviolet light in sunlight is absorbed by the vibrating electron clouds, and almost none makes it to the surface of the Earth.

This leaves us with the question as to why lights on police and some emergency vehicles are blue. Wouldn’t it make sense  not  to use blue, since at a large distance the blue light would scatter and make the lights hard to see?

A close up of a car

Description automatically generated In fact, police and emergency vehicles use all sorts of lights. Blue lights continue to be used because they are restricted to these vehicles by law, so they are uncommon. When you do see a blue light you are immediately alerted.
But these vehicles also use red lights, which don’t dim as much with distance, and powerful flashing white strobe lights which, because of their intensity, will carry over great distances regardless of their colour. Flashing lights ahead of you on the road can make it difficult for you to estimate how far ahead the emergency vehicle is, so they also use non-flashing lights.

Share:

Share on facebook
Share on twitter
Share on pinterest
Share on linkedin
Share on reddit
Share on print

Click Below For More Great Resources

 Accounting Essay

 Anthropology Essay

 Architecture Essay

 Art Essay

 Biology Essay

 Botany Essay

 Brand Management Essay

 Business Communication Essay

 Business Development Essay

 Business Essay

 Business Plan

 Business Research Methods Essay

 Chemical Analysis Essay

 Chemistry Essay

 Civil Engineering Essay

 Communications Essay

 Comparative Literature Essay

 Construction Management Essay

 Consumer Behaviour Essay

 Copywriting Essay

 Criminology Essay

 Earth and Environmental Sciences Essay

 Econometrics Essay

 Education Essay

 Educational Research Essay

 English and Linguistics Essay

 English Language Essay

 English Literature Essay

 Environmental Sciences Essay

 Film Studies Essay

 Finance Essay

 Financial Accounting Essay

 Forensic Psychology Essay

 History Essay

 Human Resources Essay

 Human Rights Essay

 Humanities Essay

 Industrial Engineering Essay

 Information Technology Essay

 Integrated Marketing Communications Essay

 International Business Essay

 International Hospitality Management Essay

 International HRM Essay

 Internet Marketing Essay

 Introduction to Business Essay

 Law Essay

 Linguistics Essay

 Literature Essay

 Management Essay

 Management Information Systems Essay

 Market Research Essay

 Marketing Essay

 Marketing Management Essay

 Media Studies Essay

 Music Essay

 Nursing Essay

 Philosophy Essay

 Political Science Essay

 Project Management Essay

 Psycholinguistics Essay

 Psychology Essay

 Religion Essay

 Science Essay

 Social Sciences Essay

 Sociology Essay

 Strategic Management Essay

 Strategic Marketing Essay

 Technology Essay

 Training and Development Essay

 Travel and Tourism Essay

 University Application

 World Literature Essay

 Zoology Essay

Most Popular

Get The Latest Updates

Subscribe To Our Newsletter

No spam, just notifications about new products, updates and discounts.

Categories

Related Posts

How to Write a Media Studies Essay

Writing a Well-Organised Media Studies Essay   [imageeffect type=”frame” width=”250″ height=”188″ alt=”” url=”wp-content/uploads/2012/09/media-studies-.jpg” ]   For any student studying a media-related course, it is essential

How to Write a Humanities Essay

[imageeffect type=”frame” width=”250″ height=”188″ alt=”” url=”wp-content/uploads/2013/02/Humanities-Essay.jpg” ] Graduate Research is fully aware of the challenges that students endure while learning how to write a humanities

How to Write a Linguistics Essay

[imageeffect type=”frame” width=”250″ height=”188″ alt=”” url=”wp-content/uploads/2013/07/linguistics-essays.jpg” ]  How to Write a Linguistics Essay Understanding how to write a linguistics essay will be critical during your

Need Help?

Our Academic Writing Services can help with all question types and formats.

What you can expect:

  • 100% Custom writing answering your question, task or requirement
  • Critical argument and reasoning
  • Logically structured
  • Full and complete reference list
  • Free similarity check

Contact Us

Get in touch to discuss your requirements or use the online order form to place your order

Pay Securely

Pay with confidence and confidentiality using our secure online payment portal

Take Delivery

Download your completed project. Expertly researched and written to your instructions