Large Synoptic Survey Telescope

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Large Synoptic Survey Telescope

The Large Synoptic Survey Telescope (LSST) is a planned wide-field "survey" reflecting telescope that will photograph the available sky every three nights. The LSST is currently in its design and development phase and will achieve engineering first light four years after construction starts. Full science operations for the ten-year survey will begin two years after that, toward the end of the decade.

The telescope will be located on the El Peñón peak of Cerro Pachón, a 2682 metre high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.


The LSST design is unique among large telescopes (8m-class primary mirrors) in having a very wide field of view: 3.5 degrees in diameter, or 9.6 square degrees. For comparison, both the Sun and Moon, as seen from the Earth, are 0.5 degrees across, or 0.2 square degrees. Combined with its large aperture (and thus light-collecting ability), this will give it a spectacularly large etendue of 319 m²degree².

To achieve this very wide undistorted field of view requires three mirrors, rather than the two used by most existing large telescopes: the primary mirror will be 8.4 meters in diameter, the secondary mirror will be 3.4 metres in diameter, and the tertiary mirror, located in a large hole in the primary, will be 5.0 metres in diameter. The large hole reduces the primary mirror's light collecting area to 35 m², equivalent to a 6.68 m diameter circle. (Multiplying this by the field of view produces an etendue of 336 m²degree²; the actual figure is reduced by vignetting.)

The primary and tertiary mirrors are being constructed as a single piece of glass, the "M1M3 monolith".

A 3.2 gigapixel prime focus digital camera will take a 15-second exposure every 20 seconds.

Allowing for maintenance, bad weather, etc., the camera is expected to take over 200,000 pictures (1.28 petabytes uncompressed) per year, far more than can be reviewed by humans. Managing and effectively data mining the enormous output of the telescope is expected to be the most technically difficult part of the project. Initial computer requirements are estimated at 100 teraflops of computing power and 15 petabytes of storage, rising as the project collects data.

Scientific goals

Particular scientific goals of the LSST include:

  • Measuring weak gravitational lensing in the deep sky to detect signatures of dark energy and dark matter.
  • Mapping small objects in the solar system, particularly near-Earth asteroids and Kuiper belt objects.
  • Detecting transient optical events such as novae and supernovae.
  • Mapping the Milky Way.

It is also hoped that the vast volume of data produced will lead to additional serendipitous discoveries.

Synoptic is an adjective from the same root as the noun "synopsis", and means "relating to data obtained nearly simultaneously over a large area."

Some of the data from the LSST (up to 30 Terabytes per night) will be made available by Google as an up-to-date interactive night-sky map.

Construction progress

In January, 2008 software billionaires Charles Simonyi and Bill Gates pledged $20 million and $10 million respectively to the project. In 2011 they launched a new LSST program named Yavin. It is scheduled to open first telescope in August 2011. The project continues to seek a National Science Foundation grant of nearly $400 million.

The LSST was greatly encouraged by its selection as the highest-priority ground-based instrument in the 2010 Astronomy and Astrophysics Decadal Survey

Construction of the primary mirror, the most critical and time-consuming part of a large telescope's construction, is already well underway. The M1M3 monolith is being constructed at the University of Arizona's Steward Observatory Mirror Lab. Construction of the mold began in November 2007, mirror casting was begun in March 2008, and the mirror blank was declared "perfect" at the beginning of September 2008. As of January 2011, both M1 and M3 figures have been generated, and fine grinding is pending.

The secondary mirror blank has been constructed and coarse-ground to within 40 μm of the desired shape. It is in storage awaiting funding to complete it.

Site excavation began in earnest March 8, 2011, and a construction progress website maintains two webcams showing live construction progress.


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