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Sunday, March 13, 2011

True beauty: Blue Mountain


It was the school holidays again and we traveled to Sydney to visit our son, Ridhwan. On the fourth day of our visit, we decided to have a look at the infamous Blue Mountain and rented a car to drive a town called Katoomba. It was a long and exhausting trip but as we passed through Katoomba town, we were rewarded by the most beautiful sight of the Blue Mountain. Everyone were tired after the long journey, but as my son pointed to a place at the far end of the town, we were totally mesmerized...! The whole valley was blue and it was a picture of beauty...something that I have never seen before. The feeling that I felt when I saw the Blue Mountains was the same as what I felt when I passed trough a small, dark tunnel and see the magical Taj Mahal at the other end of it. Hypnotised, wonderment..there were just no words that give justice to its beauty...........

Of course the question came into my head was, why blue? I argued with my son that the phenomenon was not due to the reflection of blue light from the leaves of the trees, as I did not see any blue leaves around me. Being myself, I will never be happy until I get the answers to my question, so rushed to a gift shop nearby and looked for souvenir books that explain the blue colour of the mountain. Then I found it..! The Eucalyptus tree..the gum.!

So my next mission was to look for the trees. How does it look like? I believed the trees that I found in this picture was one of them. The leaves were green, so why blue?
Syafiqah & me on a misson to search for the gum tree (nothing blue found..)
This is how it looked like from above. Slightly purplish..still not blue. The air around the trees seemed clear and normal and not hazy like in the first picture.

Here they are..! But still not blue..
Well, the explanation is like this. The mountain has high density of eucalyptus tree (as seen in the picture above) which release gum in the form of tiny droplets of eucalyptus vapour. White light is made up of several colours; red, orange,blue etc...with red having the largest wavelength and blue having one of the shortest wavelengths. The atmosphere is filled with finely dispersed droplets of oil, dust particles and water vapour will scatter short-wave length rays of light which are predominantly blue.


This type of scattering is called the Rayleigh scattering. Water and dust particles are often quite large for Rayleigh scattering to occur. However, the abundance eucalyptus vapour in the atmosphere allows Rayleigh's scattering as their sizes are smaller than the wavelength of the colour scattered. So when white light enters the particle, mostly blue colour will be scattered as blue has a very small wavelength (about 400 nm compared to 700 nm in red light). However, a different type scattering (Mie scattering) occurs for red light  that results in red sky during sunset. 


http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
So what we actually saw was the end product of the scattering, which is like a blue haze. Having figured out the reason for the blue colour gave me the satisfaction of enjoying the scenic view of the Blue Mountain. I'm glad that the authorities have taken measures to preserve the trees. The Blue Mountain is now in the World Heritage list. The view is breathtaking, and I hope that it will remain so..