The Large Synoptic Survey Telescope (LSST) would employ the most ambitious optical sky survey approach yet and would revolutionize investigations of transient phenomena. It would address the pressing and fundamental question of why the expansion rate of the universe is accelerating, and would tackle a broad range of priority science questions ranging from understanding the structure of our galaxy to elucidating the physics of stars. LSST (Figure 7.8) opens a new window on the time-variable universe and therefore promises discoveries yet to be imagined. LSST’s observations repeatedly cover large areas of sky following a preordained and optimized sequence to create a data set that addresses a majority of SFP-identified questions.
LSST’s dark energy program centers on using weak gravitational lensing to constrain the rate of growth of large-scale structure, as well as detecting supernova explosions. For these studies LSST’s data are an essential complement to the near-infrared measurements performed by WFIRST from space. LSST’s data set would permit both real-time investigations for studying variable objects and a vast archive that will be mined far into the future. In time-domain studies, LSST’s specific goals include mapping of near-Earth objects (as mandated by Congress), supernovae, gamma-ray bursts, variable stars, and high-energy transients. Its archival science will include mapping the Milky Way and the distant universe, creating an accurate photometric and astrometric data set, studying stellar kinematics, and performing a census of the solar neighborhood. It is also seen as a prime discovery engine.
LSST is proposed as an 8.4-meter telescope to be sited in Chile. It is specially designed to produce excellent images over a very wide 3.5-degree field of view. It will image the sky repeatedly in six colors in the visible band (0.3 to 1.0 micrometer). Over its lifetime of 10 years, it will observe each region of the sky 1,000 separate times. The 1,000 separate images will be used to make a “cosmic movie” to search for objects that move or whose brightness varies. By adding these images, it will also produce a very deep map of roughly half of the entire sky. LSST will produce a calibrated data set and analysis tools for the astronomy and astrophysics community. It will also facilitate the creation, by researchers outside the project, of additional science products that may be incorporated into the LSST data system. The data will be open access with no proprietary period for U.S. and Chilean astronomers; other non-U.S. partners that join will be expected to contribute to the cost of operations. LSST was conceived as a joint NSF-DOE project, with the latter taking responsibility for the camera. It has benefited from private donations and has acquired international partners. The combined primary-tertiary mirror has been cast and the grinding has begun.