This page provides a high-level introduction and summary of the SDSS project.

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Overview

The Sloan Digital Sky Survey (SDSS) is a wide field optical and infrared sky survey operating since 1998, producing both imaging and spectroscopic observations.  SDSS operates in distinct independent periods called "phases", with distinct survey programs operating within each phase.  Each phase is organized and orchestrated by the SDSS Collaboration, an international group of universities and facilities providing technical and scientific expertise.  Phases help delineate SDSS surveys, data releases, and timeframes.  SDSS has primarily been a northern hemisphere sky survey, operating out of Apache Point Observatory, a 2.5m telescope in New Mexico.  Starting in SDSS-IV, they expanded into the southern hemisphere with APOGEE-2, observing on the DuPont Telescope, a 2.5m telescope in Chile.  See the SDSS Instruments page for more information.   "Legacy SDSS" refers to SDSS phases 1 and 2, which ran from 2000-2008, which includes the original optical imaging survey, as well as several spectroscopic surveys.  From SDSS-III onwards, SDSS has been observing in spectroscopic mode only.   SDSS-III ran from 2008-2014, and consisted of four main survey programs: BOSS, APOGEE, MARVELS, and SEGUE-2.  SDSS-IV ran from 2014-2020, and consisted of three main survey programs: eBOSS, a continuation of BOSS, APOGEE-2, a continuation of APOGEE that also expanded into the southern hemisphere, and MaNGA, a wide-field optical extragalactic IFU spectroscopic survey.  eBOSS had two sub-programs: Spiders and TDSS, while MaNGA had one sub-program: MaStar.  SDSS I-IV used a fiber plug-plate system for spectroscopic observations.  This system consisted of aluminum plates with pre-drilled holes at specific on-sky positions for a pre-selected hour angle.  Each hole was manually plugged with a fiber optic cable which fed into the relevant instrument spectrographs. See Completed Surveys for more information on past SDSS.  Legacy SDSS spans a wide range of scientific sub-fields, from BAO signal measured from high-redshift quasars and LRGs, to a complete chemical composition of MW stars in the infrared, to a wide-field IFU survey of ~10k low-redshift galaxies.  

SDSS-V is the current operating phase of SDSS, with 3 full-sky survey programs: Black Hole Mapper (BHM), Milky Way Mapper (MWM), and Local Volume Mapper (LVM).  The fiber plug-plate system has been replaced with a new Robotic Focal Plane System, in both the North and South hemispheres (one BOSS spectrograph was moved to the south).  See SDSS-V Instruments for more information.  The FPS system now consists of ~500 robotic fiber positioners that can reconfigure themselves for new observations every 15 minutes.  The new FPS system allows for rapid full-sky observations of many targets.  The FPS system is used for BHM and MWM, often collectively referred to as MOS (Multi-Object Survey).  LVM consists of 4 0.16 m telescopes (1 science, 2 sky + 1 standards), armed with a ~1800 fiber IFU bundle, and operating in the South at Las Campanas.  

Phases 

A table of all SDSS operating periods over the years. 

Surveys

A table of all surveys operated by SDSS over the years. For more information, the SDSS Surveys page provides a summary and links for which surveys are currently available at MAST.

Other SDSS Resources

The following websites are useful resources for more information about SDSS:

• The current SDSS homepage, for SDSS-V
• The SDSS-IV homepage
• The legacy SDSS homepage
• The SDSS-V datamodels
• The SDSS-IV datamodels 
• The SDSS Science Archive Server (SAS) 
• The SDSS Catalog Archive Server (CAS)