Sunday, January 2, 2011

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.[5]
Large Synoptic Survey Telescope
Telescope Render 4 Aug no back copy.jpg
Organization LSST Corporation
Location El Peñón, Chile
Coordinates 30°14′39.6″S 70°44′57.8″W / 30.244333°S 70.749389°W / -30.244333; -70.749389Coordinates: 30°14′39.6″S 70°44′57.8″W / 30.244333°S 70.749389°W / -30.244333; -70.749389[1]
Altitude 2,662.75 m (top of pier)[2]
Wavelength 320–1060 nm[3]
First light Fall 2015[3]
Telescope style Paul-Baker/ Mersenne-Schmidt wide-angle[4]
Diameter 8.4 m[3]
Secondary dia. 3.4 m
Tertiary dia. 5.0 m
Angular resolution 0.7″ median seeing limit
0.2″ pixel size[3]
Collecting area 35 m²[3]
Focal length 9.9 m
Mounting altitude/azimuth

The digital camera for the LSST.



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.[3]
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.[3] (Multiplying this by the field of view produces an etendue of 336 m²degree²; the actual figure is reduced by vignetting.)
The primary/tertiary mirror was built as a monolithic unit.[6] Construction of the mold began in November 2007 at the University of Arizona's Steward Observatory Mirror Lab,[7] mirror casting was begun in March 2008,[8] and the mirror blank was declared "perfect" at the beginning of September 2008.[9] A 3.2 gigapixel prime focus[10] digital camera will take a 15-second exposure every 20 seconds.[3]
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.[11]
In January, 2008 software billionaires Charles Simonyi and Bill Gates pledged $20 million and $10 million respectively to the project. The project continues to seek a National Science Foundation grant of nearly $400 million.[12]

Scientific goals

Particular scientific goals of the LSST include:
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[13]) will be made available by Google as an up-to-date interactive night-sky map.[14]

See also


  1. ^ Charles F. Claver; et al. (2007-03-19), LSST Reference Design, LSST Corporation, pp. 64–65,, retrieved 2008-12-10  The map on p. 64 shows the Universal Transverse Mercator location of the centre of the telescope pier at approximately 6653188.9 N, 331859.5 E, in zone 19J. However, those UTM coordinates appear to be using the PSAD56 (La Canoa) datum, as other assumptions do not lead to a peak. This is apparently widely used in South American UTM grids. The coordinates above have been translated to WGS84.
  2. ^ LSST Summit Facilities, 2009-08-14,, retrieved 2009-08-21 
  3. ^ a b c d e f g h LSST Basic Configuration, LSST Corporation,, retrieved 2008-01-28 [dead link]
  4. ^ Willstrop, R. V. (October 1, 1984), "The Mersenne-Schmidt: A three-mirror survey telescope", Monthly Notices of the Royal Astronomical Society 210 (3): 597–609, ISSN 0035-8711,, retrieved 2008-01-23 
  5. ^ LSST Observatory - News & Events
  6. ^ Steward Observatory Mirror Lab Awarded Contract for Large Synoptic Survey Telescope Mirror
  7. ^ LSST Observatory - Site Photos
  8. ^ LSST High Fire Event
  9. ^ Giant Furnace Opens to Reveal 'Perfect' LSST Mirror Blank, LSST Corporation, 2009-09-02,, retrieved 2008-09-03 [dead link]
  10. ^ The camera is actually at the tertiary focus, not the prime focus, but being located at a "trapped focus" in front of the primary mirror, the associated technical problems are similar to those of a conventional prime-focus survey camera.
  11. ^ Boon, Miriam (2010-10-18), "Astronomical Computing", Symmetry Breaking,, retrieved 2010-10-26 
  12. ^ Dennis Overbye (January 3, 2008). "Donors Bring Big Telescope a Step Closer". The New York Times. Retrieved 2008-01-03. 
  13. ^ Matt Stephens (2008-10-03), Mapping the universe at 30 Terabytes a night: Jeff Kantor, on building and managing a 150 Petabyte database, The Register,, retrieved 2008-10-03 
  14. ^ Google Joins Large Synoptic Survey Telescope (LSST) Project

External links


Neil B said...

Thanks, Steven. This is one of the best overviews of an instrument and mission within reasonable space that I've seen on blogs. It's a rather amazing instrument, a wide-field type of that huge primary diameter. I remember when some people thought we wouldn't go past 6m for a long time, after Palamar and the equivocal Russian experiment with the 6-meter Bol'shoi Teleskop Azimultal'nyi (BTA). But now such large scopes are all over.

Also, I learned a new word "etendue," surprising me that after all these years of interest in astro and optics I did not pick up yet.

BTW I surmise if an optical system could produce etendue greater than source, it could be used to violate 2nd Thermo, since it could focus IR rays more intensely than from the emitter - thus keeping it's target warmer than that emitter forever.

Steven Colyer said...

Hey man, you're welcome. I didn't even know this thing existed 3 days ago. Here's how I found out about it.

I was in Borders Books the other day, doing what I usually do, which is checking out the Science magazines, then moving over to the Physics and Maths section of books. (I could live there, honestly.)

Anyway, you know how I love those UK series of books that start off with "50 Things You Should Know...", right? Well, there's a new one, about the Universe. <== linked

So I skim-read it, and bought it of course because it's only $6.00, and the info density, even if it's only of an introductory nature, is tremendous.

Anyway, the kicker for me buying it was my obsession, hitherto unknownst but now revealed, with the whole crazy Filaments/Voids Large-Scale structure of our Universe. "Beautifully weird", I call it.

And in the timeline blurb at the bottom of the page, I read about this telescope. It lists it as going on-line in 2015. Well, that won't happen, I guess we'll just have to settle for New Horizons that year, right? Good enough for me.

But as the book stated, our current telescope in this regard exploring LSS is the Sloan telescope in the US Southwest. The LSST will massively increase the detail and thus our knowledge. Can't wait, but ... what choice do we have?

"In the future, we'll know more."
... Lee Smolin