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.

THE END TEXT FROM TWINSTAR.ORG

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