Astronomy: Recommended

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For each object, the following data are included when available:

basic data:
stars: object types, coordinates, proper motion, radial velocities, parallaxes, spectral type, magnitudes and fluxes for several wavelengths and notes;
Coordinates are stored in the ICRS system.
galaxies: object types, coordinates, redshifts, integrated magnitudes and fluxes for several wavelengths, morphological type, and dimension;
cross identifications of stars and galaxies from more than 7000 source catalogues and tables, either completely or partially included in the data base. A complete list of the nomenclature used is available as the Second Reference Dictionary of the Nomenclature of Celestial Objects outside the Solar System (Lortet et al., 1994).
observational data (also called measurements), for about thirty different data types.
general bibliography for the object, including references to all published papers from the journals regularly scanned (currently about 80 titles), and access to abstracts for a few recent periodicals (A&A, ApJ, AJ, PASP). Articles are scanned in their entirety, and references to all objects mentioned are included in the bibliography. A link is provided to the ADS services as well as the journal sites.

SIMBAD offers the following functionalities:

Query by identifiers and around identifiers
Query by coordinates, specifying the radius and the equinox
Query by bibcode and partial bibcode
Sampling with a set of physical criteria
Query by lists of objects, coordinates or bibcodes
Display charts for list of objects resulting from coordinates query

Moreover, the interface provides links with many other data services :

Links to the other CDS services: Tables in VizieR, giving access to the whole catalogued data, links to Aladin images, surveys and observatory logs.
Through the coordinates in basic data, you can query around an object, using a provided radius.
Identifiers are linked to the nomenclature dictionary, providing full description of original list, and, when available, offering direct access to the corresponding catalogue in the CDS catalogue service (VizieR and Bazaar)
Every bibcode is a link to the underlying bibliographic information, either at CDS, at ADS, or at the journal site when available. Links to the full text of paper are available in most cases.
For articles containing tables stored at CDS, the reference provides also a link to the table or catalogue.
A link to the Heasarc database (NASA/GSFC) is proposed when an object has identifiers in high energy catalogues.
IUE measurements contain an anchor which points to the spectra stored in the INES database.
The maps produced by coordinate queries are cliquable and return the object information from SIMBAD.