Sloan Digital Sky Survey
From WikiSky
The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico begun in 2000.
Named after the Alfred P. Sloan Foundation, it aims to map 25% of the sky and obtain observations on around 100 million objects and spectra for 1 million objects. The main galaxy sample has a median redshift of 0.1; there are redshifts for luminous red galaxies as far z=0.4, for quasars as far as z=5; and the imaging survey has been involved in the detection of quasars beyond a redshift 6.
In the year 2006 the survey entered a new phase, the SDSS-II, by extending the obervations to explore the structure and stellar makeup of the milky way, the SEGUE and the Sloan Supernove Survey, which watches after supernovae Ia events to measure the distances to far objects.
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Observations
SDSS uses a dedicated 2.5-m wide-angle optical telescope, and takes images using photometric system of five filters (named u, g, r, i and z). These images are processed to produce lists of objects observed and various parameters, such as whether they seem pointlike or extended (as a galaxy might) and how the brightness on the CCDs relates to various kinds of astronomical magnitude.
Using this data targets are also selected for spectroscopy. The telescope is capable of recording 640 spectra at any one time by feeding an optical fibre for each through holes drilled in an aluminium plate. Each hole is individually positioned for the target in question.
Sloan Legacy Survey
The survey covers over 7.500 square degrees of the Southern Galactic Cap with data from nearly 2 million objects and spectra from over 800.000 glaxies and 100.000 quasar. This information of the position and distants of the objects allowed to investigate for the first time the large scale structure of the universe with its void and filaments.
SEGUE
The Sloan Extension for Galactic Understanding and Exploration searches for the spetra of 240.000 stars with typical radial velocity of 10 km/s for obtaining the structure of the Milky Way and investigating the formation of components.
Sloan Supernova Survey
Tries to find hundreds of Supernovae Ia until the year of 2007. The survey reapidly scans a 300 square degree area to detect variable objects and supernovae. For now it has detected 139 confimed Supernovae Ia events.
Data access
The survey makes the data releases available over the Internet. The SkyServer provides a range of interfaces to an underlying Microsoft SQL Server. Both spectra and images are available in this way, and interfaces are made very easy to use so that, for example, a full color image of any region of the sky covered by an SDSS data release can be obtained just by providing the coordinates. The SkyServer also provides a range of tutorials aimed at everyone from schoolchildren up to professional astronomers.
The raw data (from before it was processed into databases of objects) is also available through another Internet server, and through the NASA World Wind program.
Results
Along with publications describing the survey itself, SDSS data has been used in publications over a huge range of astronomical topics. The SDSS website has a full list of these publications covering distant quasars at the limits of the observable universe, the distribution of galaxies, the properties of stars in our own galaxy and also subjects such as dark matter and dark energy in the universe. See also Sloan Great Wall.
