SDSS Spectra
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About the Data
The observations come from the SDSS’s component extended Baryon Oscillation Spectroscopic Survey (eBOSS), which has measured optical spectra (3600-10400 Ångstroms) for millions of galaxies and quasars.
Individual spectra are available as FITS files. Each file follows the structure of the SDSS spec-lite file format, containing the coadded spectrum (HDU 1 COADD), spAll row (HDU 2 SPALL), and spZline row (HDU 3 SPZLINE) – but not the individual exposures (HDUs 4+), which are available only through the equivalent full spec files on the Science Archive Server.
For a full description of the file format, see the documentation of SDSS spec files from the SDSS data model.
The same FITS files can also be accessed through the SDSS Science Archive Server website, along with many related files describing various aspects of the SDSS spectroscopic data model.
Data Volume Structure
The root level of the Data Volume contains the single directory spec-lite, indicating that the contents are SDSS spec-lite files. The next level down organizes the data by run2d, which indicates which version of the SDSS spectroscopic pipeline had been run to process the spectra in that subfolder. Because different pipeline versions were used by different surveys and programs, the run number indicates when and why the spectra were collected.
The most recent spectra come from SDSS Data Release 16 and have run2d value v5_13_0; most users will want this version. The list below shows which run2d values correspond to which datasets. Within each run2d directory, spectra are organized by the SDSS plate used for the measurement; each plate-based directory contains either 640 or 1,000 FITS files, one for each spectrum collected by the plate.
Guide to run2d numbers
v5_13_0contains all optical spectra released as part of Data Release 16v5_10_0contains all optical spectra released as part of Data Release 14104contains all optical spectra collected by the SDSS SEGUE-2 survey in 2008-2009, and some other preliminary spectroscopic data collected in the same period, first released in DR7103contains all optical spectra collected by the SDSS SEGUE-1 survey’s cluster studies in 2004-2008 (part of DR7)26contains all other optical spectra from SEGUE-1 and the original SDSS Legacy Survey, observed 2000-2008 and released in DR7
The following query gives summary data about each of these runs, including the SDSS survey and program responsible for the data:select cast(run2d as int) as run, survey, programname, count(*) as nPlates, min(dateObs) as startDate, max(dateObs) as endDate from platex where run2d in ('26','103','104') group by cast(run2d as int), survey, programname order by cast(run2d as int), survey, programname