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------------------------------------- - 1845 - Why is the sky blue?
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- The child may ask you, “ Why is the sky blue?” You may have the answer but it took 100 years of science for the answer the first time. This is a short cut to a century of learning and an introduction to the teachers who gave it to us.
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- Aristotle wrote a treatise on the answer: “ The air close at hand is clear and the deep air of the sky is blue in the same way that a thin layer of water is clear, but, a deep well of water looks black.”
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- Aristotle’s ( 384 - 322 B.C.) parents died when he was a young age and he was raised by a family friend.. At 17 he went to Athens to Plato’s academy. In 342 B.C. he became the tutor of Alexander the Great. His writings accumulated to 150 volumes. He became the founder of the systematic study of logic and the art of reasoning.
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- Later Johan Kepler said, “the air merely looks colorless because the tint of its color is so faint when it is in a thin layer. But, the idea of “ blueness” was not mentioned..
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- Kepler (1571 - 1630) a German astronomer at the age of 23 he was teaching science in a university in Austria. Kepler’s book published in 1619 includes his 3rd law that the square of the period of revolution of a planet is proportional to the cube of its distance from the Sun. He corresponded with Galileo. He had 13 children and was killed by a medical bleeding operation designed to reduce his high fever.
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- Leonardo da Vinci said, “ the blue which is seen in the atmosphere is not its own color, but, is caused by heated moisture having evaporated into the most minute imperceptible particles, which beams of the solar rays attract and cause to seem luminous against the deep, intense darkness of the region of fire that forms a covering above them.”
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- - Leonardo de Vinci ( 1452 - 1519) born of illegitimate birth near Florence, Italy. He became a military engineer and he drew pictures of tanks, airplanes, parachutes and submarines. He was a vegetarian due to an aversion to killing animals. Yet, he studied muscles and bones in order to enhance his drawings including the “ Mona Lisa” and “Last Supper”.
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-Isaac Newton tried to demonstrate the phenomena through painstaking experiments with refraction that white light could be decomposed into its constituent colors of the rainbow.
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- Isaac Newton (1642 - 1727) graduated from Cambridge 1665. He worked out the binomial theorem while on his Mother’s farm where he stayed to avoid the Plague that was in London. It was on the farm that he saw the apple fall to the ground and wondered why the Moon did not fall as well.
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- He concluded that the force of gravity fell off as the square of the distance from Earth’s center. Newton discovered the prism to show that white light was a rainbow of colors combined. At 27 he became a professor at Cambridge U. He developed Calculus. He theorized that light was a series of particles (photons). In 1668 he invented the reflecting telescope using a parabolic mirror. His book in 1687 codified Galileo’s 3 laws of motion, F=ma. Then, the force of gravity F= G*m*M / r^2. In 1727 he was buried in Westminster Abbey.
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- In 1760 Leonhard Euler speculated that the wave theory of light might help to explain why the sky is blue
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Lenard Euler (1707 -1783) was a professor of math in St. Petersburg, Russia. He lost the sight of his right eye observing the Sun. With one eye and later in 1766 loosing sight in that eye he published 800 papers on mathematics.
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- Scientists in 1789 were making countless observations from different locations, altitudes and times, using cyanometers. A cynanometer is a 53 section tool with varying shades of blue arranged in a circle. The thinking that something suspended in the air must be responsible for the blue color.
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- Eventually it was realized that gaseous molecules were that “something” that was making air appear blue.
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- The blueness of the sky helped science discover the physical reality of atoms. The color of the sky is deeply connected to atomic theory.
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- The sky is blue because the incident light interacts with gas molecules in the air. More of the light is in the blue part of the spectrum and is scattered because the wavelength is the size of the air molecules. What reaches our eyes is scattered blue light.
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- All the frequencies of the incident light can be scattered but the high frequency , short wavelength, blue is scattered more than the low-frequency, wide wavelength, red light. This explanation won a Noble price in 1870.
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- In 1904 Lord Rayleigh discovered the gas molecule argon when a wavelength of light is on the same order as the size of the molecule the intensity of the scattered light varies inversely with the 4th power of its wavelength. (That is: the shorter the wavelength the greater the intensity of scattering ).
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- Lord Rayleigh (1842 - 1919) was an English physicists credited with mathematically confirming that light scattering accounts for the blueness of the sky. He showed that all atomic weights are multiples of the hydrogen atom.
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- But, violet is shorter wavelength then blue. The sky should appear violet? Now, we enter biology. Our eyes are more sensitive to blue light than to violet light. The ultraviolet light that burns your skin is invisible to your eyes.
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- To explain “ Why is the sky blue” you need several sciences to understand the colors of the rainbow in the visual spectrum.
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--------------------------- The wave nature of light, being electromagnetic radiation.
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-------------------------- The geometry of which sunlight hit’s the atmosphere. At the lowest angles of sunset the sky turns orange and red. Because the blue light has been scattered out of the spectrum in the deeper atmosphere viewed at the lower angles.
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-------------------------- The size of nitrogen and oxygen molecules.
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------------------------- The way the human eyes perceive colors.
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-------------------------- How the curiosity of a child can lead to a century of science.
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- Keep your curiosity as long and as childish as you can as you grow older and wiser.
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- Request these Reviews to learn more:
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- #1795 - lists 12 reviews about light. Light travels 1 foot in a nanosecond. Time stops at the speed of light. A telescope shows you the oldest thing, a young star that is 12 billion years old today.
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- #1848 - That includes a biography of these great scientists listed in this review.
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----- 707-536-3272 ---------------- Thursday, September 26, 2019 -----
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