The Sloan Digital Sky Survey began in 1988. As already indicated, it was a direct consequence of our building a 3.5-meter optical telescope at Apache Point Observatory. Scientifically, the project was conceived by Jim Gunn, Rich Kron, and myself. When we started discussions, we had no money and we had no idea where the project would go. We did not understand that if we could accomplish our goal, it would have an enormous impact on astronomy.
In brief, we designed and built a 2.5-meter telescope with (at that time) the world's largest CCD camera and two spectrographs, each capable of observing 320 objects at one time, in total more than ten times the number of any other telescopic system. The camera consisted of 30 large CCDs, six for each of 5 color filters. The telescope drifted across the sky with the net result of producing 5-color images of every object in the sky. From this massive amount of data, objects were selected for spectroscopic follow-up. The images were obtained on the very best nights of the year; when the weather was not so good, we would put on the spectrographs and proceeed with the recording of spectra.
The project was designed with one goal in mind: to build a digital, searchable archive of 200 million galaxies and 1 million quasars. We produced over 30 times the amount of information per night than any other telescope of any size and we reached our goal in eight years, over 100 times faster than could have been done with any other telescope of the same size. The net outcome, as of 2008, was a contiguous map of 10,000 square degrees on the sky in five color filters; millions of spectra of galaxies, quasars, and stars; a legacy of over 3000 research papers; and a public archive. Perhaps most importantly, the public archive has set the standard for what is now called "big data": enormous public archives of some aspect of the physical world which are readily available to the public and are searchable.
Jim, Rich, and I each had our own reasons for becoming involved in the inception of the SDSS. Rich has spent his whole career discovering quasars: massive black holes at the centers of galaxies which glow by accreting atoms. He thought at the time (1988) that doing this job right required a project of the scope of the SDSS. We don’t really know about quasars; we have a model, a picture of what they are, but you are never sure about the real thing. How does material flow into the central black hole engine for instance, and where does it come from? Or, how are black holes created? Quasars may look different at different times of their life cycle over millions and millions of years. At times, there may be no light, at times there may be lots of light, and there may be many types of quasars that are just inherently different. Classifying and understanding quasars can therefore be expected to require the acquision of a very, very large sample of objects. SDSS, we knew, would find hundreds of thousands of quasars, thus taking our understanding of quasars to a new level.
Apache Point Observatory: Apache Point Observatory in the Sacramento Mountains of New Mexico. The Sloan Digital Sky Survey's 2.5-meter telescope is on the left. White Sands National Monument is visible in the distance, above the telescope. The monitor telescope, used for calibrations, is inside the small dome to the right of center. Optical fibers for spectroscopy are pre-positioned each day in the building on the right (behind the trees). The building in the center rolls on rails to cover the 2.5-meter telescope when it is not in use.
Credit: Sloan Digital Sky Survey