Saturday, March 10, 2007

137)The bending and scattering of light in the recent total lunar eclipse.

The recent total lunar eclipse, seen very clearly in some parts of the world and not so clearly in others, provides for us an informative lesson on the properties and optics of light, an offspring of one of the four forces of nature discovered so far, the Electromagnetic Force. The force carrier for this fundamental force of nature is called a photon, which is a single unit particle of light.

In the scenario of a total lunar eclipse our moon and earth are aligned in such a way that the earth completely obstructs the sun's direct illumination of the moon: the earth is situated between the sun and the moon, completely blocking off the light of the sun shining directly on the moon; theoretically, one should not be able to see the moon at all in a situation like this. Nevertheless, despite this total blocking off, citizens of planet earth still saw the moon illuminated by a reddish-brown colour. This colour and phenomenon are caused by two properties of light: refraction and scattering.

Refraction is the bending of light as it passes from one medium to another: it is light showing the wave aspect of its dual wave-particle nature. In the case of the total lunar eclipse, sunlight, streaming from behind onto the earth, which has totally blocked off the light from directly reaching the moon, nevertheless is refracted by the earth's atmosphere and bends around the edge of the earth to shine on the moon. As the light comes around the earth and through our atmosphere, it is scattered by both air molecules and dust particles present in the atmosphere. However, only the short wavelength components of white light(violet and blue) are scattered away whereas the longer wavelength components of white light(yellow, orange and red) penetrate through the atmosphere and shine onto the other side, which is what gives us our lovely and colourful sunsets(and sunrises) and what gave the moon, during the totality of its eclipse, its reddish-brown colour.

Here are some marvellous pictures of the total lunar eclipse, courtesy of NASA's Astronomy Picture of the Day website, as well as an explanation of our glorious sunsets within the context of the scattering and refraction of light:


Islam, eminently logical, placing the greatest emphasis on knowledge, purports to understand God's creation:Aga Khan 4.
The God of the Quran is the One whose Ayats(Signs) are the Universe in which we live, move and have our being:Aga Khan 3