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--------------------------------- 2618 - SUN - learning closer than ever?
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- The “Parker Solar Probe“, which launched in August 2018, is flying closer to the visible surface of the sun than any spacecraft to date. That trajectory carries the spacecraft deep into the sun's atmosphere, called the corona, where the probe's instruments focus on the spacecraft's immediate surroundings, measuring magnetic fields and particles of plasma, the charged soupy state of matter that makes up the sun.
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- “Solar Orbiter” won't fly as close to the sun, but it brings unique skills. First, it carries two types of instruments. One set, like Parker's, will study the spacecraft's surroundings; the other, a set of telescopic instruments, will observe the visible surface of the sun itself at a distance.
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- Then partway through its mission, Solar Orbiter will leave the belt around the sun's middle, called the ecliptic, and begin circling the sun at a tilt, allowing the spacecraft to use those telescopic instruments to produce the first-ever images of the sun's poles.
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- The National Science Foundation's Inouye Solar Telescope is stuck here on Earth, and construction is still underway. But once all of its instruments are operational, there will be plenty more images like the "caramel corn" picture that scientists published this January, the highest-resolution solar image to date.
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- The “Inouye Solar Telescope” is a microscope on the sun. The observatory will measure the wavelengths of light emitted by the sun and decipher the magnetic signature of light that is under the influence of the sun's magnetic field.
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- We have so few close-up observations of the sun that being able to compare two separate locations is automatically valuable, no matter where each spacecraft is. Combining the data from all three observatories is vital for scientists to accomplish the goal that drives the missions: to understand the sun and its influence throughout the solar system. The impacts of the sun across the solar system as a set of phenomena called “space weather“.
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- In Earth's neighborhood, space weather can interfere with the technology modern society is ever more reliant upon, particularly navigation and communication satellites. Space weather is also a hazard for astronauts traveling farther from Earth, as it can harm both their technology and their bodies.
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- Solar scientists want to be able to predict space weather in much the same way meteorologists predict terrestrial weather. Scientists just don't know enough about how the sun works.
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- Understanding space weather could tell scientists where to look for signs of life elsewhere in the universe. After all, while we humans have a soft spot for the sun, it's just a star like any other. This means that scientists can apply what these three missions discover to all the stars we'll never be able to see as clearly. And while space weather is vexing to Earth, it could be deadly in solar systems that surround smaller, more active stars.
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- And there should be plenty for the trio of projects to study in the coming years. Right now, the sun is pretty quiet, but over the next five or six years, the sun's activity will increase and both the Parker Solar Probe and the Solar Orbiter will be on hand to see what happens during that period.
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- They are really, truly voyages of discovery, and we're doing fundamental physics and understanding how a star works.
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- Ancient astronomers had a really tough time predicting solar eclipses, sometimes with dire results. For a particularly gruesome example, we have a story passed down to us of Hi and Ho, the court astrologers of the emperor K'ang of ancient China. Apparently they were out drinking one night and somehow neglected to predict the eclipse of 2159 B.C. The emperor was not pleased. They were beheaded.
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- Hi and Ho were not exactly fully to blame. Solar eclipses were notoriously hard to predict. While they occur roughly every couple of years somewhere on the Earth, for any region the size of a country you had to rely on complex and intricate cycles within cycles within cycles to even come close to finding a rhythm. That is, until the ultimate Power Couple of gravity came onto the scene.
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- Isaac Newton figured out something absolutely remarkable about gravity that no one else had ever realized: that it's universal. According to Isaac himself, the thought struck him when he watched an apple fall from a tree as he was relaxing at his mom's house one lazy afternoon.
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- He saw the apple fall in a straight line toward the Earth. We have all seen this exact same thing, but in that moment Newton saw something stunning. He saw the apple accelerate from being still to moving. And all accelerations require a force. So, the Earth was applying a force to the apple even though it wasn't touching it. Amazing!
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- Isaac also knew that every action has an equal and opposite reaction. If the Earth is applying a force to accelerate the apple, then the apple must be applying a force to accelerate the Earth. Whatever this force of gravity is, it must be mutual and in both directions. The reason the apple moves more than the Earth is because the mass of the Earth is so much greater. It just appears like that apple is doing all the moving and the Earth is doing all the work, when in Newton's suddenly much clearer vision, all things were equal when it comes to forces.
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- If the Earth is applying gravity to the apple and the apple is applying gravity to the Earth, then this force of gravity must be operating with all pairs of objects simultaneously all across the universe. In other words, gravity must be universal.
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- Newton worked out the implications of this newfound universal force of gravity, and instantly many things clicked into place. He was even able to predict the speed of the moon in its orbit.
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- He was able to re’ derive Kepler's laws from much simpler principles. And he was able to explain the motions of all the planets and all the moons around those planets. And then he took all this fantastic work, wrote it in a book, and put the book on a shelf and forgot about it
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- It sat there for years until one of his friends, Edmond Halley, started agitating for him to publish it. Apparently, for Newton, unlocking the secrets of universal gravity was just an idle afternoon pastime and not something worthy of serious academic interest. But Halley knew better. He constantly pressed, and probably annoyed, Newton until he finally published his work.
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- Edmond Halley then took this newfangled theory of universal gravitation and went solving almost every single problem known to plague astronomers. Most notably, he figured out the regular pattern of a particular comet that now bears his name by digging into the historical records and using that data to feed into calculations of a prediction of its reappearance.
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- By digging into the ancient records, Halley was able to predict an upcoming total solar eclipse over his home city of London. Using Newton's theory of universal gravitation, Halley predicted the eclipse of May 3, 1715, to an accuracy of a four minutes.
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- That's right. Four minutes. Without any calculator or computer. Just using historical records and Newton's laws, Halley nailed the first-ever accurate prediction of a solar eclipse, something that had bedeviled astronomers ever since the unfortunate days of Hi and Ho thousands of years ago.
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- Now we want to learn enough about the sun to predict sunspots, sun flares, and other solar activity that will affect communications and electric power distribution here on Earth.
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- See Review 2613 “Sunspots follow 11-year cycle”
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- See Review 2599 “The end of humanity” that lists 19 more reviews about the sun. A big topic!
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- February 13, 2020 2618
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--------------------- Friday, February 14, 2020 --------------------
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