This is an outline of how to delve into the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR). It is an evolving and incomplete document. See the glossary at the end for definitions of capitalized Words. Pat Hall -- pathall[at]astro.princeton.edu
If you're serious about using the EDR, sign up for the SDSS User's Group at least, and perhaps the User's Forum as well.
The EDR can be accessed online through the Multi-mission Archive at Space Telescope (MAST). The EDR consists of 460 square degrees of five-color (u'g'r'i'z') imaging data, a catalog of 10 million objects from that data, and spectroscopy for 55,000 of those objects. A quick introduction to the dataset and access methods can be found at the MAST Getting Started page. The EDR User's Guide is a more detailed introduction. The rest of this page summarizes how to access specific data types. If a query or connection fails, check the status of the archive servers as well as the syntax of your query.
SPECTRA (This is what I am most familiar with.) Spectra are available in both FITS and GIF format. (1) Individual: You can request individual 1-D spectra by Plate/MJD/Fiber or RA/DEC. Here you can also access the raw 2-D spectra by Plate/MJD if need be. (Both these interfaces may be phased out soon.) (2) Batch: You can batch-request 1-D spectra (in a single tar, gzipped tar, or pkzipped file) if you know their FieldID, MJD, and Fiber numbers. (3) You can also batch-request 1-D spectra of objects within a certain radius of some position AND which meet certain criteria in the photometric catalog by doing a request here, browsing the results as HTML, marking the desired records, adding the marked records to your shopping cart, and finally retrieving the desired data products for everything in your shopping cart (in a single tar, gzipped tar, or pkzipped file).
CATALOG DATA (1) Simple search: Use the SDSS Catalog Search form to search the SDSS Catalog by object name or position, possibly modified by simple selections on object type, magnitude, and/or color. You can browse the results as HTML or download them as a FITS table or as ASCII files in CSV (Comma Separated Values) format. (2) Advanced search: you will need to install the SDSS science archive Query Tool (sdssQT or sxQT), a GUI running under Tcl/Tk (so, yes, if you don't have Tcl/Tk running you'll need that too). You will want to read the Online Manual and the Class Overview. You use sdssQT to query the EDR database using SQL (Standard Query Language). Each object has various parameters which are stored in different classes. For example, photometric information such as magnitudes and positions are stored in the PhotoObj class, and spectroscopic information such as redshifts and spectral classifications are stored in the SpecObj class. Learning what is stored where will ease the task of searching through the EDR database. If you are at Catolica, sdssQT and Tcl/Tk are installed on chavez (PU/PUC postdocs only) and piscis. On piscis, to get going type 'setenv SXQT_DIR /usr/local/sdssQT/' and then '/usr/local/sdssQT/bin/sdssQT &'.
IMAGES (This is what I am least familiar with.) The imaging data are available as photometrically and astrometrically calibrated images in five wavebands in FITS format: the CORRECTED FRAMES have 0.4 arcsecond pixels; the BINNED IMAGES are sky images with 1.6 arcsecond pixels and detected objects subtracted. Cut-out pixel maps, called ATLAS IMAGES, are also available for each detected object in the catalog. MASK FILES showing the areas excluded from the catalogs for whatever reason are available, but software to decode them is not (yet). FIELD SUMMARIES detailing the number of objects in each field and other parameters are available as FITS tables. Also available (though not yet in batch mode) are three-color composite images known as RECONSTRUCTED FRAMES. (1) Individual Objects: You can request Atlas Images or corrected or reconstructed frames by entering RA/DEC pairs or SDSS Run/Rerun/camcol/FieldId/Object ID numbers for a list of objects (This interface may be phased out soon.) (2) Specific Objects: you can request image products for a list of objects (in a single tar, gzipped tar, or pkzipped file) via their RA/DEC, their NED or SIMBAD names, or their SDSS Run/Rerun/camcol/FieldId/Object ID numbers. (3) Categories of Objects: You can also batch-request images of objects within a certain radius of some position AND which meet certain criteria in the photometric catalog by doing a request here, browsing the results as HTML, marking the desired records, adding the marked records to your shopping cart, and finally retrieving the desired data products for everything in your shopping cart (in a single tar, gzipped tar, or pkzipped file).
GLOSSARY Field Each camera column (camcol or scanline) in a Strip is broken down into a number of slightly overlapping Fields on which Photo is then run. Photo The atlas image creation, object detection, and photometry pipeline. Plate A plug-plate of 640 fibers. Each spectrum is uniquely identified by its Plate number, the MJD (Modified Julian Date) of the observation, and the Fiber number. (The same Plate can have different pluggings on different MJDs.) Run Each time the imaging camera is powered up is a different Run. Rerun Each reduction using a new version of the pipeline is a different Rerun. Strip 6 scanlines of imaging data separated by about one scanline width each (a scanline is the track of one camera column across the sky). Stripe Two Strips are merged into a filled Stripe about 2.5 degrees wide.