The Large Synoptic Survey Telescope
Harold II had recently crowned himself king despite his father's promise to cede England to William, Duke of Normandy. Now King Harold awaited the powerful Duke's response. His astronomers scanned the heavens for some portent of their sovereign's success or a harbinger of his doom. On the 24th of April 1066, they noticed a bright new star --in fact an apparition of Halley's Comet in its 76-year orbit about the sun. Cognizant of massing Norman forces across the channel, the astronomers foretold Harold's defeat. In a depiction from the Bayeaux Tapestry, he is shown receiving this news amid visions of William's invading fleet arriving on his shores.
In modern times, though astronomers have traded augury for insight, scanning the heavens for change is increasingly proving key to understanding a dynamic universe. Daily brightness fluctuations first revealed the existence of supermassive black holes in the cores of quasars. Stellar explosions, lasting only a few weeks yet visible across much of the universe, have recently provided evidence for a previously unknown force of nature. Though searching the heavens for signs of doom had fallen into disrepute since the Enlightenment, even this practice has been given new urgency with the realization that Earth's collisions with other solar system bodies continues to play a major role in its evolution, even posing a threat on human time scales to civilization itself.
Observations of change in the universe are often difficult to obtain. The most fundamental obstacle is that much of this change is so slow it could never be observed directly. Much as geological change is inferred on Earth, long-term change is perceived in the heavens by recognizing a temporal progression among seemingly disparate objects. Astronomers have become adept at this process and have built up a remarkably detailed picture of the evolution of stars, galaxies, and even the universe as a whole.
Despite the slow progress of cosmic evolution, many of the most remarkable astronomical events occur on human, and even daily, time scales, yet these changes have proven the most difficult to observe. The impediment to observing rapid change and to the more detailed insight it engenders lies in the nature of the tools currently available to astronomers. Modern large telescopes are truly marvels of design, with light-gathering power improving on the naked eye more than a million-fold.
Yet remarkable as they are, they have all been designed to look very deeply at very small parts of the sky. Their small field of view means that any one observation is not likely to catch a transient event in the act — we are always looking somewhere else. A small field also means that an impractically large number of separate observations is required to map the entire sky to the depth these telescopes permit and reveal the rare missing links among more common objects. These facilities are few in number and viewing time on them is in great demand worldwide. With the assignment of only a few nights per year to each astronomer, it is difficult to make progress on a wide variety of fronts.
This lack of continuous access and a global view means we are almost certainly missing most of what's going on in the universe. Our all-sky maps are made with small telescopes, inexpensive enough to be dedicated to a single purpose, but limited in the depth and detail they can achieve. Their limited light-gathering capability also means that such maps take years to complete, making it nearly impossible to detect change. Such slow progress across the sky gives serendipity little chance most of what we know about transient events is discovered accidentally. Since cosmic cartography is limited not by distance but by the amount of light which can be collected on Earth, we are as ignorant of faint nearby objects as we are of bright objects at the edge of the observable universe.
Current large telescopes are the high temples of astronomy, the inner sancta to which only the Initiated have access. Most observatories practice some sort of outreach, and remarkable images are widely available, but there is no way schools and the general public can look deeply and at will into the heavens.