Transcript
WHY IS THE OCEAN BLUE?
Nothing is as mesmerising as the ocean’s
blue colour - but what makes it blue?
SEEN FROM SPACE, LIGHT FROM
THE SUN IS WHITE
BUT WHEN IT HITS OUR
ATMOSPHERE AND THE OCEANS
BENEATH IT, DIFFERENT
COLOURS BEGIN TO BEHAVE
DIFFERENTLY
IN THE ATMOSPHERE, BLUE LIGHT
IS SCATTERED AND RED LIGHT
ABSORBED,
TO A SMALL DEGREE
A PROCESS CALLED
RAYLEIGH
SCATTERINGLORD RAYLEIGH
THE WAVELENGTH WITH THE
HIGHEST SCATTERING RATE IS
AROUND THE VISIBLE SPECTRUM,
MORE PRECISELY AT 418NM
THIS SPECIFIC WAVELENGTH IS
SEEN BY HUMANS AS THE
COLOUR BLUE
OTHER COLOURS, SUCH AS
GREEN, YELLOW AND
RED, HAVE PROGRESSIVELY
LOWER SCATTERING AND HIGHER
ABSORPTION RATES.
GOING BEYOND THE VISIBLE
SPECTRUM, INTO SHORTWAVE
ULTRAVIOLET OR LONGWAVE INFRARED,
ABSORPTION RATES ARE 10,000,000 TIMES
HIGHER.
THE OCEAN’S SURFACE LAYER IS PRACTICALLY
BLOCKING THOSE WAVELENGTHS.
YOU MAY WONDER WHY WATER
IS TINT-FREE IN OUR
EVERYDAY LIVES?
THE REASON IS THAT RAYLEIGH
SCATTERING NEEDS LARGER
QUANTITIES TO BECOME EVIDENT.
THE MORE WATER IS ADDED, THE
BLUER IT WILL LOOK.
CURIOUSLY, AN OCEAN OF THE
SAME CHEMICAL COMPOSITION
AS ON EARTH, BUT LOCATED ON
SOME FAR-AWAY PLANET
CAN BE A COMPLETELY DIFFERENT
COLOUR, SUCH AS VIOLET.
WE (SADLY!) DO NOT HAVE
VIOLET OCEANS BECAUSE:
1. HUMAN EYES AREN’T GREAT
AT DETECTING VIOLET
2. IT FORMS ONLY A MINOR PART
OF OUR SUN’S SPECTRUM
3. IT CAN BE ABSORBED BY THE
OZONE LAYER
WHY IS THE OCEAN BLUE?
WELL, SOMETIMES
IT ISN’T!
BONDI BEACH AUSTRALIA
QINGDAO CHINA
LAKE RETBA
WATER ON EARTH OFTEN DEFIES
CONVENTION, TURNING
DIFFERENT COLOURS – AND IT’S
USUALLY ALGAE TO BLAME.
IMAGE CREDITShttps://www.flickr.com/photos/tiarescott/
https://www.flickr.com/photos/provoost/
http://en.wikipedia.org/wiki/John_William_Strutt,_3rd_Baron_Rayleigh#mediaviewer/File:John_William_Strutt.jpg
https://www.flickr.com/photos/acbo/
https://www.flickr.com/photos/giantginkgo/
https://www.flickr.com/photos/oneras/
https://www.flickr.com/photos/polandeze/
https://www.flickr.com/photos/zoomion/
https://www.flickr.com/photos/alpoma/
http://galleryhip.com/lake-retba-salt.html
http://www.dailymail.co.uk/news/article-2239040/Crimson-tides-Tourists-flee-Bondi-Beach-Red-Sea-rare-algae-bloom-turns-water-colour-blood.html
http://www.mirror.co.uk/news/uk-news/sea-of-green-as-algae-invasion-hits-142431
top related