SCIENCE AND TECHNOLOGY

Deep blue sky :

This colour of sky means the sky is very clean. This often occurs when a cold front brings clean air from the north, or when clean air from the ocean moves onto land.

Medium blue sky :

This colour of sky means there is lots of water vapor in the sky. It can also suggest the presence of sulfur from coal-burning operations. It may be caused by the chemical emissions of plants and trees.

Pale or milky-white sky :

This colour of sky indicates considerable air pollution from coal-burning power plants or chemical power plants. This condition often occurs in the summer when the air is still. There are also natural causes, such as volcanic activity or ocean plankton etc.

Gray or dark gray : 

This colour of sky cause of  the smoke from forest fires or agricultural burns. 

Brown or brownish orange : 

Emissions from cars and trucks can cause a layer of this colour to form over the horizon. The main component of this kind of pollution is nitrogen dioxide.