- 2789 - TELESCOPES - to do a 3D map of the Universe. Since 2005, scientists have been scanning the night sky to create a three-dimensional map of our universe with the purpose of shedding light on one of the biggest mysteries in physics. The quest is to learn the true nature and identity of dark energy and dark matter.
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-------------------------- 2789 - TELESCOPES - to do a 3D map of the Universe.
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- This quest is about to get a massive upgrade with the successful installation and testing of the Dark Energy Spectroscopic Instrument, or DESI.
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- DESI features 5,000 optical fibers, each one designed to collect light from a single galaxy. DESI is to gather 20 times more data than previous surveys. This telescope looks at infrared light. This is light that has stretched out wavelengths because it has been traveling through an expanding Universe.
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- A previous instrument on a different telescope, the Baryon Oscillation Spectroscopic Survey instrument, required collaborators to drill 1,000 holes into large metal plates that held fibers in a configuration that exactly matched the position of known galaxies in a small portion of the night sky. Each time scientists wanted to image new galaxies, a new plate had to be drilled and the fibers inserted by hand.
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- With DESI, researchers have relegated the work of pinpointing galaxy locations to a hive of 5,000 robotic pencil-shaped tubes. These positioners have a precision of several micrometers, about one-10th the width of a human hair, and are capable of moving on their own to focus on distant galaxies.
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- The images they take aren't ordinary photographs. Scientists are instead interested in the type of light the galaxies emit. All galaxies are in motion, mostly moving away from each other due to the expansion of the universe. And the light from those that move away from us is stretched into the low-frequency, red part of the spectrum, much the same way that sound waves from a siren are stretched when an ambulance moves past you.
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- Scientists can use these redshifted signals to create a three-dimensional map of our universe stretching back 11 billion years into its past. By analyzing the distribution of galaxies through space and time, scientists can then make inferences about the nature of the unknown dark matter that pulls galaxies together and that of dark energy, which pushes them apart.
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- Researchers completed the first round of testing on the robotic positioners last November. A second milestone was achieved in January when the positioners were accurately pointed at over 2,000 stars simultaneously.
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- The software is a key player in choreographing the movement of all 5,000 robotic positioners simultaneously. The software guides the robotic positioners on a multistep process to locate galaxies.
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- First, the focal plane, a large metallic structure that holds the positioners in place, must be pointed at just the right portion of sky. Just as old maritime navigators would use the position of the stars to guide their way, 10 high-resolution cameras embedded in the focal plane capture and analyze light from stars, which allows researchers to orient the telescope.
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- These movements to position the focal plane have to be incredibly precise for each fiber to receive the most light that it can from its assigned galaxy. Nudged even a little off target, and the fiber will be only partially filled with its galaxy's light. But when positioned as designed, each fiber will be filled completely with the light of its galaxy, with minimal background.
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- Once the telescope is pointed in the right direction, the robotic positioners begin an intricate mechanical waltz, peering deep into the sky to detect sources of light far too faint for human eyes to see.
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- Their high degree of precision gets them most of the way to the desired galaxy, but the angle might still be slightly off for some. To get them the rest of the way, DESI has a CCD camera installed at the primary mirror of the telescope, which looks up at the focal plane.
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- Researchers use a built-in light source to illuminate the fibers embedded in the robotic positioners. The fibers project the resulting small dots of light to the CCD camera, which then images them. The software compares the positions of the fibers in the images to where they should actually be pointed based on detailed star charts from previous surveys.
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The software then computes how far off each positioner is from the desired target, after which another system can move it the rest of the way toward its designated galaxy.
- DESI is scheduled to operate for a total of five years, during which time it will measure the redshifts of over 30 million galaxies and quasars, i.e.: massive black holes. Scientists can then use this information to determine if and how the concentration of dark energy has changed throughout the history of our universe.
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- We will have a 3D map of the Universe stretched out since the beginning. This will be new eyes on the Universe. What will we see with new eyes?
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- August 12, 2020 2789
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--------------------- Thursday, August 13, 2020 -------------------------
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