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Efrem Savin
Efrem Savin

Behind The Mirrors


With mirrors around us every day, we tend to take them for granted, but what exactly is happening on a scientific level when we peer into one? And on that note, do you know the physics involved in why we see a mountain range reflected in the clear, calm lake below?




Behind the Mirrors



The metals inside mirrors perform the same trick, reflecting all the colours of the visible spectrum, but the difference is they're ultra-smooth on a microscopic level. A piece of paper might seem smooth to you, but it's not even in the same smoothness league as a mirror, and that's how a mirror image is formed: all of the light is bouncing straight back in the direction it's just come from.


The same effect is happening when ripples hit a pond - the surface is no longer flat, the light is no longer bouncing straight back, and you can no longer see your face when you peer into it. Ever since we've been able to perfect the manufacture of mirrors, they've become useful in science, transportation and many other fields.


Kant has maintained that our consciousness[3] or our description and judgments about the world could never mirror the world as it really is so we can not simply take in the raw data that the world provides nor impose our forms on the world.[4] Lorenz disputed this, saying it is inconceivable that - through chance mutations and selective retention - the world fashioned an instrument of cognition that grossly misleads man about such world. He said that we can determine the reliability of the mirror by looking behind it.[2]


In March, New York City renter Samantha Hartsoe shared that she felt a cool draft from behind her bathroom mirror. Intrigued, she decided to take down the mirror to investigate the breeze, and found a gaping hole leading into a mysteriously empty room.


James Webb Space Telescope's primary mirror at NASA Goddard. The secondary mirror is the round mirror located at the end of the long booms, which are folded into their launch configuration. Webb's mirrors are covered in a microscopically thin layer of gold, which optimizes them for reflecting infrared light, which is the primary wavelength of light this telescope observes. Photo: NASA/Chris Gunn


Once in space, getting these mirrors to focus correctly on faraway galaxies is another challenge. Actuators, or tiny mechanical motors, provide the answer to achieving a single perfect focus. The primary mirror segments and secondary mirror are moved by six actuators that are attached to the back of each mirror piece. The primary mirror segments also have an additional actuator at its center that adjusts its curvature. The telescope's tertiary mirror remains stationary.


One further challenge is to keep Webb's mirror cold. To see the first stars and galaxies in the early Universe, astronomers have to observe the infrared light given off by them, and use a telescope and instruments optimized for this light. Because warm objects give off infrared light, or heat, if Webb's mirror was the same temperature as the Hubble Space Telescope's, the faint infrared light from distant galaxies would be lost in the infrared glow of the mirror. Thus, Webb needs to be very cold ("cryogenic"), with its mirrors at around -220 degrees C (-364 degree F). The mirror as a whole must be able to withstand very cold temperatures as well as hold its shape.


NASA set out to research new ways to build mirrors for telescopes. The Advanced Mirror System Demonstrator (AMSD) program was a four-year partnership between NASA, the National Reconnaissance Office and the US Air Force to study ways to build lightweight mirrors. Based on the ASMD studies, two test mirrors were built and fully tested. One was made from beryllium by Ball Aerospace; the other was built by Kodak (formerly ITT, now the Harris Corporation) and was made from a special type of glass.


A team of experts was chosen to test both of these mirrors, to determine how well they worked, how much they cost, and how easy (or difficult) it would be to build a full-size, 6.5-meter mirror. The experts recommended that the beryllium mirror be selected for the James Webb Space Telescope, for several reasons, one being that beryllium holds its shape at cryogenic temperatures. Based on the expert team's recommendation, Northrop Grumman (the company that led the effort to build Webb) selected a beryllium mirror, and the project management at NASA Goddard approved this decision.


The James Webb Space Telescope's 18 special lightweight beryllium mirrors made 14 stops to 11 different places around the U.S. to complete their manufacturing. They came to life at beryllium mines in Utah, and then moved across the country for processing and polishing. In fact, the mirrors made stops in eight states along the way, visiting some states more than once, before they journeyed to South America for lift-off and the beginning of their final journey to space. Explore an interactive map showing the journey of the mirrors.


The beryllium to make Webb's mirror was mined in Utah and purified at Brush Wellman in Ohio. The particular type of beryllium used in the Webb mirrors is called O-30 and is a fine powder. The powder was placed into a stainless steel canister and pressed into a flat shape. Once the steel canister was removed, the resulting chunk of beryllium was cut in half to make two mirror blanks about 1.3 meters (4 feet) across. Each mirror blank was used to make one mirror segment; the full mirror is made from 18 hexagonal segments.


SSG/Tinsley started by grinding down the surface of each mirror close to its final shape. After this was done, the mirrors were carefully smoothed out and polished. The process of smoothing and polishing was repeated until each mirror segment was nearly perfect. At that point, the segments traveled to NASA's Marshall Space Flight Center in Huntsville (MSFC), Alabama for cryogenic testing.


The change in mirror segment shape due to the exposure to these cryogenic temperatures was recorded by Ball Aerospace Engineers using a laser interferometer. This information, together with the mirrors, traveled back to California for final surface polishing at Tinsley. The mirrors' final polish was completed in June of 2011.


Some Technical Details: How is the gold applied to the mirrors? The answer is vacuum vapor deposition. Quantum Coating Incorporated didthe coatings on our telescope mirrors. Essentially, the mirrors are put inside a vacuum chamber and a small quantity of gold is vaporized and it deposits on the mirror. Areas that we don't want coated (like the backside and all the mechanisms and such) are masked-off. Typical thickness of the gold is 1000 Angstroms (100 nanometers). A thin layer of amorphous SiO2 (glass) is deposited on top of the gold to protect it from scratches in case of handling or if particles get on the surface and move around (the gold is pure and very soft).


After the gold coating was applied, the mirrors once again traveled back to Marshall Space Flight Center for a final verification of mirror surface shape at cryogenic temperatures. The mirror segments were now complete. Next, they traveled to NASA's Goddard Space Flight Center in Greenbelt, Maryland.


The first two flight mirrors arrived at NASA Goddard in September of 2012. By the end of 2013, all the flight primary mirror segments, as well as the secondary and tertiary mirrors would be at Goddard. The mirrors were stored in special protective canisters in the cleanroom, awaiting the arrival of the flight telescope structure. Engineers inspect one of the first two flight mirrors to arrive at NASA Goddard.


The flight telescope structure (essentially the bones of the telescope, which the mirrors would be mounted on) was shipped from Northrop Grumman, and arrived at NASA Goddard in August of 2015. It was moved to the assembly stand in November of 2015. On November 22, 2015, the first mirror was installed.


Once the mirrors were completed, the science instruments were integrated into the telescope. While at Goddard, the telescope also underwent environmental testing - both acoustic and vibration - to ensure it would be able to withstand the rigors of launch. That successfully completed, the telescope was sent off to NASA Johnson in Houston, Texas, for tests of the optics and instruments at cryogenic temperatures. NASA Johnson's Chamber A is the only thermal vacuum chamber NASA has that is large enough for Webb!


These corrections were made through a process called wavefront sensing and control, which aligns the mirrors to within tens of nanometers. During this process, a wavefront sensor (NIRCam in this case) measured any imperfections in the alignment of the mirror segments that prevented them from acting like a single, 6.5-meter (21.3-foot) mirror. Engineers used NIRCam to take 18 out-of-focus images of a star - one from each mirror segment. The engineers then used computer algorithms to determine the overall shape of the primary mirror from those individual images, and determined how they must move the mirrors to align them.


The World Behind the Mirror is a realm that is accessible behind all mirrors. Once a person is in this world, he or she can't use magic, but they can touch various mirrors to see what is happening in the world that the mirrors on the other side exist in. There exists a way out of this world, a shattered mirror. Next to it is a pillar with a pile of broken pieces of it. If someone were to complete the mirror, it would activate a portal inside it.


At an unknown point in time, the Genie of Agrabah ends up here after being framed for killing King Leopold, and this is how he communicates through the Evil Queen's mirrors. He begins working on a portal to escape his prison but he doesn't finish building it. ("Fruit of the Poisonous Tree", "I'll Be Your Mirror")


The Dragon is banished to the World Behind the Mirror when the Evil Queen traps him here. He remains alone until Emma and Regina arrive after the Queen imprisons them within the mirror as well. The Dragon reveals there is one possible way to escape the realm through a portal that Regina's Magic Mirror, Sidney, was working on when he was trapped here. Despite his best efforts, the Dragon cannot not finish it, though he suggests that if the three of them work together, they may have better luck. Before they can accomplish much, the Queen speaks through the Dragon with his heart, taunting Emma and Regina, before revealing herself in one of the mirrors with Henry. She then orders the Dragon to kill Emma and Regina, and he, unable to disobey her command, transforms into a gigantic dragon. As he rampages, Emma and Regina duck behind a pillar and determine that if they can get the Dragon to blast the mirror with his fire breath, it could break and release them from this world. Henry helps them by using Hephaestus's Hammer on the mirror's other side, breaking Emma and Regina free. As the Dragon's fire breath bursts through the mirror, Henry grabs the Dragon's heart to preserve it. Regina later frees the Dragon. ("An Untold Story, "I'll Be Your Mirror", "Mother's Little Helper") 041b061a72


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