WHY IS SKY BLUE ?(CLASS 10)

IT'S A MYTH THAT THE SKY IS BLUE BECAUSE IT REFLECTS THE BLUE OF THE SEAS AND OCEANS WHICH COVER ALMOST 71% OF THE EARTH'S SURFACE. MOST PEOPLE ALSO THINK AND SAY THAT EARTH'S ATMOSPHERE AND A PROCESS KNOWN AS SCATTERING THAT CAUSES OUR SKIES TO LOOK BLUE TOO

SO, HERE COMES THE QUESTION IN EVERY HUMAN MIND THAT WHAT IS THE TRUTH BEHIND THE MOST COMMON QUESTION "WHY IS SKY BLUE?" SO, LET'S FIND OUT THAT "WHY IS SKY BLUE?"

WHY IS THE SKY BLUE? (IN SHORT):

1. AS WHITE LIGHT PASSES THROUGH OUR ATMOSPHERE, TINY AIR MOLECULES CAUSE IT TO 'SCATTER'.

2. THE SCATTERING OF LIGHT CAUSED BY THESE TINY AIR MOLECULES (KNOWN AS RAYLEIGH SCATTERING) INCREASES AS THE WAVELENGTH 

3. DO YOU KNOW WHICH COLOR HAS THE SHORTEST WAVELENGTH? OK, LET ME TELL YOU. ITS VIOLET AND BLUE HAVE THE SHORTEST WAVELENGTH AND RED COLOR HAS THE LONGEST.

4. SO, THEREFORE BLUE LIGHT IS SCATTERED MORE THAN RED LIGHT  AND THE SKY APPEARS BLUE DURING THE DAY.

5. DURING THE SUNRISE AND SUNSET THE LIGHT HAS TO TRAVEL FURTHER  THROUGH THE EARTH'S ATMOSPHERE.

6. WE DON'T SEE THE BLUE LIGHT AT THAT TIME BECAUSE IT GETS SCATTERED VERY MUCH SO THE SKY APPEARS RED.

SCATTERING OF LIGHT:

AS WE KNOW WE ARE SURROUNDED BY THE EARTH'S ATMOSPHERE AND IS COMPOSED OF LOTS OF DIFFERENT  AIR MOLECULES. SUNLIGHT CAN BE REDIRECTED BY  THE AIR MOLECULES AND THIS IS KNOWN AS  SCATTERING. THE SIZE OF THE MOLECULES IS MUCH SMALLER THAN THE WAVELENGTHS OF LIGHT WHICH IS VISIBLE TO US AND SO THE TYPE OF SCATTERING THAT OCCURS IS KNOWN AS RAYLEIGH SCATTERING. THIS TYPE OF SCATTERING INCREASES AS THE WAVELENGTH OF LIGHT DECREASES SO BLUE LIGHT IS SCATTERED MORE THAN RED LIGHT BY THE TINY AIR MOLECULES PRESENT IN EARTH'S ATMOSPHERE.

WHY IS SKY BLUE IN DAY TIME:

IN THE MORNING TIME, WHEN THE SUN IS OVERHEAD IT APPEARS WHITE. THIS IS BECAUSE THE LIGHT TRAVELS A SHORTER DISTANCE THROUGH THE ATMOSPHERE TO US; IT SCATTERED A VERY LITTLE, EVEN THE BLUE LIGHT. DURING THE DAY SKY LOOKS BLUE BECAUSE ITS THE BLUE LIGHT THAT GETS'S SCATTERED THE MOST. IT'S REDIRECTED INTO MANY DIFFERENT DIRECTIONS ALL OVER THE SKY, WHEREAS THE OTHER WAVELENGTHS AREN'T SCATTERED AS MUCH.

WHY IS THE SKY RED DURING SUNRISE AND SUNSET?

DURING THE TIME OF SUNRISE AND SUNSET, THE SKY APPEARS TO CHANGE COLOUR. WHEN THE SUN IS LOW IN THE SKY, THE LIGHT HAS TO TRAVEL. A LONGER DISTANCE THROUGH THE ATMOSPHERE BY WHICH THE EARTH IS SURROUNDED SO WE DON'T SEE THE BLUE LIGHT BECAUSE IT GET'S SCATTERED AWAY. INSTEAD OF ALL THE OTHER COLORS, WE SEE THE RED AND ORANGE LIGHT THAT TRAVELS TOWARDS US SINCE THE LIGHT HASN'T BEEN SCATTERED VERY MUCH. HENCE THE SUN AND SKIES LOOK REDDER AT THE TIME OF SUNRISE AND SUNSET.

IS SKY BLUE ON OTHER PLANETS TOO?

NOW WE WILL TALK ABOUT THE APPEARANCE OF THE SKY ON OTHER PLANETS, SO LET'S CONTINUE. OTHER PLANET'S DON'T HAVE AN ATMOSPHERE EXACTLY LIKE EARTH AND SO SO THEIR SKIES WOULD LOOK DIFFERENT.

FIRST LET'S TALK ABOUT MARS. MAR'S ATMOSPHERE IS MUCH THINNER THAN THE EARTH'S - LESS THAN 1%. THE LOW DENSITY OF AIR MOLECULES MEANS THAT THE RAYLEIGH SCATTERING, WHICH CAUSES OUR SKIES TO BE BLUE ON EARTH, HAS A VERY SMALL EFFECT ON MARS.

HOWEVER, DURING A SUNRISE AND SUNSET ON MARS, THE SUNLIGHT TRAVELS A LONGER DISTANCE THROUGH ITS ATMOSPHERE AND IT'S ALIKE TO THE THICKNESS OF THE ATMOSPHERE ON EARTH. AS SUCH, THE BLUE LIGHT GETS SCATTERED IN ALL DIRECTIONS AND THE LONGER WAVELENGTHS OF LIGHT DON'T GET SCATTERED MUCH AT ALL PROVIDING A BLUE GLOW TO THE SKY AROUND THE SUN IN THE HOURS AROUND DAWN AND DUSK.

SKY COLOR ON MOON:

THE SKY FROM THE MOON WOULDN'T EVEN APPEAR TO HAVE ANY PARTICULAR COLOUR. THE MOON'S ATMOSPHERE IS SO THIN THAT IT VIRTUALLY DOESN'T HAVE ONE. WHEN THE AIR IS TOO THIN FOR GAS MOLECULES DON'T COLLIDE WITH EACH OTHER WE CALL IT AN EXOSPHERE INSTEAD. BECAUSE OF THE LACK OF AN ATMOSPHERE, SUNLIGHT ISN'T SCATTERED AND SO WHETHER IT'S DAYTIME OR NIGHTTIME ON THE MOON, THE SKY APPEARS BLACK.