Time is an emerging property of matter
What is the Digital Sky Survey?
Simply put, the Sloan Digital Sky Survey is the most ambitious astronomical survey ever undertaken. The survey will map a quarter of the entire sky in detail, determining the positions and absolute magnitudes of hundreds of millions of celestial objects. It will also measure distances to more than a million galaxies and quasars.
The SDSS addresses fascinating, fundamental questions about the universe. With the help of the survey, astronomers will be able to see the large-scale patterns of the galaxies: sides and spaces across the universe. Scientists have many ideas about how the universe might have evolved and different patterns of large-scale structures from different theories. The Sloan Digital Sky Survey will tell us which theories are correct - or whether we need to come up with entirely new ideas.
Making cards is a central activity of human knowledge. The last decade has seen an explosion in the scale and density of mapmaking endeavors, with areas as disparate as heredity, marine science, neuroscience, and surface physics, which used the power of computers to map and understand vast and complex new territories. The possibility of absorbing and unlocking huge amounts of data in a short period of time is changing the image of science. The Sloan Digital Sky Survey will bring this modern application of comprehensive mapping to cosmography, the science of mapping and understanding the universe.
The SDSS will make the largest map in human history. It will give us a three-dimensional picture of the universe, on a scale a hundred times larger than what has been explored so far. The SDSS will also record the distances to 100,000 quasars, the most distant objects known, giving us an unprecedented indication of the distribution of matter at the edge of the visible universe. The SDSS is the first large-scale survey to use electronic light detectors, so the resulting images are significantly more sensitive and precise than previous surveys that were based on photographic plates. The results of the SDSS are electronically available to the scientific community and the general public, both as images and in the form of accurate catalogs of all objects discovered. At the end of the survey, the total amount of data produced will be approximately 15 terabytes (trillion bytes), which will rival the information contained in all of the Library of Congress books.
By observing a large part of the sky systematically and sensitively, the SDSS will have a decisive influence on various astronomical investigations, such as the large-scale structure of the universe, the formation and development of galaxies, the relationship between dark and luminous matter, the structure of our own Milky Way, as well as the properties and distribution of the dust from which stars, like our own sun, were formed. The SDSS will become a new point of reference, an expert guide to the universe that will be used by scientists for the next several decades.
Today's universe is filled with leaves of galaxies bending through mostly empty space. Like soap bubbles in a sink, they form dense fibers with empty spaces in between. The Big Bang, our best model of how the universe began, gives us a picture of a universe filled with a hot, uniform soup of fundamental particles. Between the beginning of the universe and today, the force of gravity somehow pulled matter together into areas of high density, leaving empty spaces. What triggered this shift from monotony to structure? Understanding the origin of the structure we see in the universe today is an important part of understanding our cosmic history.
Understanding the order of matter in the universe is made difficult by the fact that the glowing stars and galaxies we see are only a small part of the whole. More than 90% of the matter in the universe gives off no light. The nature, amount and distribution of this "dark matter" are among the most important questions in astrophysics. How did the gravitation of dark matter affect the visible structures? In other words, we can use careful maps of the positions and movements of the galaxies to reconstruct the mass distribution and use it to gain clues about the dark matter.
One of the difficulties in examining the entire universe is getting enough information to be able to take a picture. Astronomers created the Sloan Digital Sky Survey to address this problem in a direct and emerging way: the SDSS collects a mass of data large and accurate enough to cover the range of astronomical questions.
The SDSS will acquire high-resolution images of a quarter of the entire sky in five different colors. From these images, advanced imaging software will measure the shape, brightness, and color of hundreds of millions of astronomical objects, including stars, galaxies, quasars (massive but very bright objects thought to be through matter falling into huge black holes, be driven), and a number of other heavenly exotics. Selected galaxies, quasars and stars will be observed using an instrument called a spectrogram, to determine the exact distances to one million galaxies and 100,000 quasars, and to provide a wealth of information about individual objects. These data will give astronomical society one of the things it needs most: a comprehensive catalog of the constituent parts of a characteristic area of the universe. The SDSS map will reveal how big the largest structures in our universe are and what they look like. It will help us understand the mechanism that turned a uniform "primeval soup" into a frothy network of galaxies.
The U.S. The Census Bureau gathers statistical information about how many people live in the United States, where they live, where they come from, their family income, and other specifics. This census becomes a primary source of information for people trying to understand the nation. The Sloan Digital Sky Survey will do a kind of celestial count that will collect information about how many galaxies and quasars the universe contains, how they are distributed, their individual characteristics, and how bright they are. Astronomers will use this information to investigate questions such as why flat spiral galaxies are found in less dense areas of the universe than football-shaped elliptical galaxies, or how quasars have changed in the history of the universe.
The SDSS will also get information about the Milky Way and even our own solar system. The vast web ejected from the SDSS telescope will capture as many stars as there are galaxies, and as many asteroids in our solar system as there are quasars in the entire universe. Knowing about these objects will help us learn how stars are distributed in our galaxy and where asteroids belong in the history of our solar system.
Rare objects are scientifically interesting by definition. By sifting through the hundreds of millions of objects captured by the SDSS, scientists will be able to compile a complete inventory of the most distant quasars, the rarest stars, and the most unusual galaxies. The most unusual objects in this directory will be about a hundred times rarer than the rarest objects currently known.
For example, stars with a chemical compound very poor in metals such as iron are the oldest in the Milky Way. You can therefore give us information about the formation of our galaxy. However, such stars are extremely rare, and only a wide, deep survey of the sky can find enough of them to form a conclusive picture.
Because they are so far away, quasars can serve as testers for intergalactic matter throughout the visible universe. In particular, astronomers can identify and study galaxies to the extent that they block certain wavelengths of light emitted by quasars behind them. Using the light from quasars, the SDSS will discover tens of thousands of galaxies in the early stages of evolution. These galaxies are too faint and indistinct for their own light to be detected by even the largest telescopes. Quasar studies will also allow scientists to study the evolution of the chemistry of the universe through its history.
Observing the universe through a telescope makes it possible not only to look into space, but also back in time. Imagine intelligent beings in a planetary system around a star 20 light years away. Suppose these beings catch a stray television broadcast from Earth. You would see events that happened on Earth 20 years earlier: for example, a newscast about Ronald Reagan's re-election (1984) would be seen 20 years later (2004). While we've seen three new presidents these days, beings would still see Reagan.
Light moves extremely fast, but the universe is a very large place. In fact, astronomers routinely look at quasars so far away that it takes billions of years for their light to reach us. When we look at galaxies or quasars that are billions of light years away, we see them as they looked billions of years ago.
By observing galaxies and quasars at different distances, astronomers can see how their properties change over time. The SDSS will measure the distribution of nearby galaxies, allowing astronomers to compare them to more distant galaxies that can now be seen with new instruments such as the Hubble Space Telescope and the Keck Telescope. Because quasars are very bright, the SDSS will allow them to study their evolution through more than 90% of the history of the universe.
The universe expands like a loaf of raisin bread in the oven. Pick a raisin and imagine it would be our Milky Way. If you think of yourself instead of the raisin, then no matter how you look at the loaf as the bread rises, all of the other raisins move away from you. The further away another raisin is from you, the faster it will move away. In the same way, the other galaxies move away from ours as the universe expands. And since the universe expands evenly, the further a galaxy is from Earth, the faster it recedes from us.
The light that comes to us from these distant objects is shifted towards the red end of the electromagnetic spectrum, in the same way that the sound of a train whistle changes as the train departs or approaches a station. The faster a distant object moves, the more it is redshifted. Astronomers measure the amount of redshift in a galaxy's spectrum to find out how far it is from us.
By measuring the redshifts of a million galaxies, the Sloan Digital Sky Survey will create a three-dimensional image of our local neighborhood in the universe.
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