Why the sun gets red during sunset? Prof Waqar Hussain

Why the sun gets red during sunset?

PROF WAQAR HUSSAIN

      Ans:- Ordinary sunlight appears as white light which contains all the colours. But we see colours only when, they are broken down as in spectrum as in a rainbow or a glass prism or by atmosphere. The dust of atmosphere screens the visible light from the sun; allowing the red, yellow and orange colours (of larger wavelengths) to get through and scatters and reflects the other 

colours like green, blue, (of shorter wavelengths), etc.  That’s why our sky looks blue.  

           At sunset, light must travel farther and longer through the atmosphere before it gets to you, so more of it is reflected and scattered and thus, the color of the sun changes, first to orange, then to red and ultimately, it appears redder and redder as it gets closer to the horizon. Because, the more and more of shorter wavelengths (blue, green) are now scattered and only the longer wavelengths (red, orange) are left for you to be seen. So, the sun appears to you red.

                   When the sun is overhead, the sunlight travels comparatively smaller distance as shown in diagram as blue line. When the sun is low in the sky, the sunlight travels larger distance and encounters more dust and air molecules as shown in diagram as red line. So, more blue light is scattered away, leaving behinds mostly the reddish component of white sunlight to journey straighter to your eyes. So the setting sun looks red. It is all the phenomenon of atmosphere and its variable thickness for the sun; when it is overhead or low in sky. If you happen to see a sunset on the moon, the sun would look white. That’s because the moon doesn't have an atmosphere.