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Why Is the Sky Blue?

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The Short Answer:

Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered more than the other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

It's easy to see that the sky is blue.

Have you ever wondered why?

A lot of other smart people have, too. And it took a long time to figure it out!

The light from the sun looks white. But it is really made up of all the colors of the rainbow.

When white light shines through a prism, the light is separated into all its colors. A prism is a specially shaped crystal.

If you visited The Land of the Magic Windows, you learned that the light you see is just one tiny bit of all the kinds of light energy beaming around the universe--and around you!

Like energy passing through the ocean, light energy travels in waves, too. Some light travels in short, "choppy" waves. Other light travels in long, lazy waves. Blue light waves are shorter than red light waves.

All light travels in a straight line unless something gets in the way and does one of these things:—

• reflect it (like a mirror)

• bend it (like a prism)

• or scatter it (like molecules of the gases in the atmosphere)

Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from low in the sky has passed through even more air than the sunlight reaching us from overhead. As the sunlight has passed through all this air, the air molecules have scattered and rescattered the blue light many times in many directions.

Also, the surface of Earth has reflected and scattered the light. All this scattering mixes the colors together again so we see more white and less blue.

What makes a red sunset?

As the sun gets lower in the sky, its light is passing through more of the atmosphere to reach you. Even more of the blue light is scattered, allowing the reds and yellows to pass straight through to your eyes.

Sometimes the whole western sky seems to glow. The sky appears red because small particles of dust, pollution, or other aerosols also scatter blue light, leaving more purely red and yellow light to go through the atmosphere.

Article Original Source : https://spaceplace.nasa.gov/blue-sky/en/

Why 1918 matters in India’s corona war

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• Over a century ago, Spanish flu all but destroyed the Indian economy. What can we learn from those experiences?

• 1918 experience matters because it was the last major pandemic that spread rapidly within India, showing what happens when an unprepared country comes in the way of a virulent pandemic

NEW DELHI : Towards the fag end of June, 1918, The Times of India Bombay carried a brief story about a “fever epidemic" that was sweeping through the city. Workshops got shut; most offices discovered that their clerical staff had suddenly taken leave en masse. But nobody realized the magnitude of what was about to unfold. The main remedy prescribed in the news article: Not to worry and go to bed.

Meanwhile, a novel flu virus had sneaked into Bombay, most likely through the city’s docks. In a span of just three weeks, by mid-July 1918, news began filtering in about the spread of this mystery illness—to Madras and Allahabad.

By October, just three months after the first cases began showing up in Bombay, the healthcare system had broken down completely. Newspapers were calling for the public to “organize self-help".

There are many differences between 1918 and 2020: India is not ruled by a colonial government; the coronavirus is technically different from an influenza virus although they cause similar symptoms; also, much of what we have come to understand as modern medicine did not exist a century ago.

India worst hit

But despite these caveats, the 1918 experience matters for one simple reason: it was the last major global pandemic that spread rapidly within India—a historical reservoir of experience that shows, in painful detail, what happens when an unprepared country comes in the way of a virulent pandemic.

That is precisely why Chinmay Tumbe, an economic historian at Indian Institute of Management Ahmedabad (IIM-A), began rifling through old archival records. “It is useful to see how bad things can be. The thing with a pandemic is that it can so easily spiral out of control," he said.

And, in 1918, all it took was a few months. An estimated 10-20 million Indians died (a fifth of the global death toll, making India the worst-hit country). The Ghats along the River Ganga ran out of wood as the bodies piled up, according to a letter written by renowned Hindi poet Nirala, which is available in his collected works. Prominent citizens from Mahatma Gandhi to writer Munshi Premchand are suspected to have fallen sick before recovering.

And, the disease left a devastating impact on the economy.

In the last 120 years of recorded economic history in India, 1918 was the worst (see Chart 1). Recorded growth in real gross domestic product (GDP) was the lowest (-10.5%) while inflation was near all-time highs, a cocktail much worse than any other tragedy that has hit India—including the world wars or the Bengal famine.

“Typically, when GDP slumps, prices also fall. But nobody was going to work in 1918 (because of the virus) and there was a supply-side shock. It was a truly unique year in India’s macroeconomic history," said Tumbe.

“We should be gearing up for something similar," he warned. While the rate of spread of the disease will depend heavily on the effectiveness of India’s containment measures (travel bans from an expanded set of countries was announced on Wednesday), the infection will spread and economic growth will fall, he added.

If 1918 is the worst-case scenario, how should India prepare for a pandemic at its doorstep? For that we have to first understand the severity of what happened more than a hundred years ago.

The 1918 H1N1 virus

In 1951, Johan Hultin, a 25-year-old microbiologist and PhD student from the University of Iowa, US, set out on an unusual mission. His destination was a graveyard frozen in permafrost nestled inside an ocean-side village in Alaska. Hultin was looking for traces of a virus, frozen in time, within the tissues of those buried during the deadliest pandemics of the 20th century.

A full reconstruction of the virus in 2005 showed that no other influenza virus was as dangerous and virulent as the one that surfaced in 1918.

Globally, the influenza pandemic of 1918 killed more people in a year than what the Black Death of the Middle Ages (bubonic plague) killed in a century; it killed more people in 24 weeks than AIDS killed in 24 years, wrote John M. Barry, historian and author, in his book The Great Influenza: the Story of the Deadliest Pandemic in History. The disease initially spread by exploiting the crowded conditions of an era in which trench warfare was the norm. The infections were noticed across military camps but countries in the midst of World War I—Britain, Germany, France and the US—kept it a secret in the begCaused by an H1N1 virus of avian origin, the disease is estimated to have infected about a third of the global population and caused at least 50 million deaths worldwide, with nearly half of the victims being men and women in their 20s and 30s.

The deaths were often violent: the infected coughed up blood; they bled from their ears and noses, and had extremely painful body aches. The pandemic took shape in two phases—a milder form in early 1918 when the virus affected the sick and the elderly, while the healthier recovered swiftly. The second wave beginning August was deadly—ravaging the stronger immune system of younger adults.

According to the Centers for Disease Control and Prevention (CDC), health protection agency of the US, the properties that made the 1918 virus so devastating were not well understood when it struck.

inning, in a bid to keep the morale of the forces high. Spain, which was not a party in the war, reported the outbreak of the disease accurately. So when the disease became a pandemic it seemed to have emerged in Spain, and hence dubbed “Spanish Flu".

Caused by an H1N1 virus of avian origin, the disease is estimated to have infected about a third of the global population and caused at least 50 million deaths worldwide, with nearly half of the victims being men and women in their 20s and 30s.

According to the Centers for Disease Control and Prevention (CDC), health protection agency of the US, the properties that made the 1918 virus so devastating were not well understood when it struck.

“Things like the Indian Premier League must shut down. It is crazy if we continue with it," he said. “And the phone caller tune message is ridiculously insufficient. We should be spreading information in every possible language through a variety of mediums."

Khan added: “The coming impact is going to be huge. This is no longer a question of if, but when. Even if this (Covid-19) doesn’t turn out to be the deadliest flu, the economic impact is going to big. We may be fast moving towards a point where there are no flights operating anywhere in the world." Preliminary estimates put losses in the aviation sector at $113 billion.

Strangely, Covid-19 may thus end up pushing the world closer to how it looked in 1918 by shutting down air travel. And that is the key difference on the negative side between now and a century ago: connectivity and ease of travel. It was a key metric that went into the World Health Organization’s (WHO’s) decision to declare a pandemic.

The advice is clear: expand surveillance. “Countries need to prepare for more hospital admissions," Soumya Swaminathan, chief scientist at WHO told Mint. “The main lesson from China is that this virus can be contained and controlled, if effective public health action is taken speedily."

Instead, we (India) have been dragging our feet for two months, said Khan. “We can’t believe that things like the weather will take care of it. If that was the case, the virus wouldn’t have spread to tropical places like Singapore and Philippines," he added.

In the next few weeks, to avoid a repeat of 1918, the key parameter beyond containment would be extensive testing of all those who exhibit cold-like symptoms, especially as many suspected patients have already been able to travel, work and socialize undetected inside the country for significant periods of time.

“We should identify cases as quickly as possible," said Lalit Kant, a researcher at the Public Health Foundation of India. “In a pandemic, quietness is always worrying. If we go by what has happened in other countries, then we should be getting prepared." (South Korea, for example, set up an extensive protocol in just a few weeks and tested more than 200,000 people).

In conclusion

Ultimately, irrespective of how the next few weeks play out, Covid-19 may change the world in profound ways, much like the 1918 influenza pandemic.

A century ago, population profiles got profoundly altered (the decade between 1911 and 1921 was the only census period in which India’s population fell). The devastation of the pandemic also, in no small part, fuelled the Indian independence movement.

In 2020, the changes may be more economic and social, if not political. Our view on vaccines and the investments that go into it, for example, may change immediately, said K.S.James, a demographer at the International Institute of Population Studies.

“Only for the last 100-or-so years, population growth above 1% a year has been common. We are fortunately living at a unique moment in time. But now, communicable diseases are making a comeback. They are leaving impacts that serious wars used to earlier. New research on vaccines is inevitable," he said.

Article Original Source : https://www.livemint.com/news/world/why-1918-matters-in-india-s-corona-war-...