The Centre de Données astronomiques de Strasbourg (CDS), known in English as the Strasbourg astronomical Data Centre, operates three services that much of the world’s professional astronomy relies on for locating, cross-referencing, and reusing published astronomical data: SIMBAD, VizieR, and Aladin. For research administrators and data stewards outside astronomy, these three names are worth knowing because together they form one of the oldest, most mature examples of what FAIR-compliant domain repository infrastructure looks like in practice, built decades before “FAIR” was a named principle. This guide explains what each service does, how the three interoperate, and why they matter when documenting astronomical data management or repository choice in a data management plan.
A note on spelling: VizieR’s internal capital “R” is a deliberate stylization used by CDS, not a typo, and the service has no relation to “vizier,” the historical court-official title. This page covers only the astronomical catalogue service operated by CDS Strasbourg.
What Is CDS Strasbourg?
CDS was founded in 1972 as the Stellar Data Centre and took its current name, the Strasbourg astronomical Data Centre, in 1983. It operates as a service of the Observatoire astronomique de Strasbourg, part of the University of Strasbourg, in partnership with France’s Centre National de la Recherche Scientifique (CNRS). CDS describes its mission as to “collect useful information concerning astronomical objects; upgrade these data by critical evaluations and comparisons; distribute the results to the astronomical community; conduct research using these data.” That collect-curate-distribute-reuse mission maps closely onto what research-data-management practitioners now call the data lifecycle: CDS has been performing lifecycle stewardship for an entire scientific discipline’s published data since well before that vocabulary existed.
Access to all three services is free and does not require registration, whether through their web interfaces or through the standardized machine-readable interfaces described below.
SIMBAD: Identifying and Cross-Referencing Astronomical Objects
SIMBAD (Set of Identifications, Measurements, and Bibliography for Astronomical Data) is CDS’s reference database for the identification, nomenclature, and bibliography of astronomical objects outside the solar system, such as stars, galaxies, and nebulae, rather than planets, asteroids, or comets within our own solar system. Its central function is disambiguation: the same star or galaxy is frequently catalogued under many different designations across different surveys and papers (for example, a single star might appear under an HD number, a Gaia source identifier, a Tycho designation, and a traditional Bayer or Flamsteed name, all referring to the same physical object). SIMBAD maintains the cross-identification between these designations, assigns each object a stable main identifier, and links every entry to the published literature that discusses it.
For a researcher, SIMBAD functions much like a combination of an authority file and a citation index: checking SIMBAD before publishing new observations of a star or galaxy is the standard way to confirm an object is being identified consistently with prior literature, rather than inadvertently creating what looks like a new discovery out of an object already well studied under a different name.
VizieR: The Catalogue Service for Published Astronomical Data
VizieR is CDS’s service for hosting and serving the data tables and catalogues published alongside astronomy journal articles, ranging from a small table of measurements in a single paper to survey catalogues covering very large numbers of sources. Where SIMBAD answers “what is this object and what has been published about it,” VizieR answers “what does the underlying tabular data actually contain.” Major astronomy journals, including Astronomy & Astrophysics, the Astrophysical Journal, and Monthly Notices of the Royal Astronomical Society, routinely require or strongly encourage authors to deposit large data tables with CDS at the time of publication rather than leaving them only as supplementary material on the journal’s own site. CDS then standardizes and hosts that data through VizieR, giving it a stable home, independently citable and discoverable apart from the publisher.
This is a genuinely useful model for research administrators outside astronomy to be aware of: it is a discipline-wide norm, enforced through journal policy rather than funder mandate, that requires a specific class of research output (large data tables) to go to a designated domain repository as a condition of publication, a practice that predates most funder-driven data-sharing mandates by decades.
Aladin: The Interactive Sky Atlas
Aladin is CDS’s interactive software for visualizing, analyzing, and cross-matching astronomical images, survey data, and catalogues, available both as a desktop application and as a browser-based “Aladin Lite” viewer embedded in many other astronomy websites and tools. Rather than working with tables of numbers directly, Aladin lets a researcher overlay SIMBAD object positions, VizieR catalogue entries, and full-resolution sky imagery from multiple surveys on the same interactive map of the sky, and interrogate them together. Aladin also serves as CDS’s primary access point into the broader Virtual Observatory (VO): the federated network of astronomical archives and services designed to be queried through shared standards rather than one at a time.
How the Three Services Work Together
SIMBAD, VizieR, and Aladin are designed to be used together rather than as three independent products. A typical workflow moves between them: a researcher might identify an object of interest in SIMBAD, pull the catalogue measurements associated with it from VizieR, and then visualize its position against sky imagery and neighbouring sources in Aladin, with each service linking directly to the relevant records in the other two. This tight integration is a deliberate design choice by CDS, and it is a large part of why the three are usually discussed together as a single “CDS services” ecosystem rather than as three unrelated tools that happen to share an operator.
Standards That Make CDS Data Interoperable
All three services are built on, and have substantially helped shape, the interoperability standards maintained by the International Virtual Observatory Alliance (IVOA). VizieR and SIMBAD expose data through IVOA’s Table Access Protocol (TAP) and Simple Cone Search interfaces, returning results in the VOTable XML format, so that Virtual Observatory tools beyond CDS’s own interfaces can query them programmatically. Aladin implements the Simple Application Messaging Protocol (SAMP), which lets it exchange data live with other VO-compliant desktop tools such as TOPCAT, and it was the original platform for HiPS (Hierarchical Progressive Survey), a format CDS developed for serving multi-resolution sky imagery efficiently over the web that has since become an IVOA standard. For a data steward evaluating whether a domain repository meets interoperability expectations, this combination of standardized query protocols, a standardized exchange format, and a shared object-identification layer via SIMBAD is close to a model case.
Why This Matters for FAIR and Open-Science Compliance
CDS’s three services predate the FAIR Guiding Principles (Findable, Accessible, Interoperable, Reusable) by decades, but they satisfy each one in a way that makes them a useful reference point for explaining what FAIR compliance looks like in a mature domain repository, including when writing a data management plan or evaluating repository options:
- Findable — SIMBAD’s stable main identifiers and VizieR’s persistent catalogue identifiers mean a specific object or dataset can be located consistently across years of subsequent literature, without depending on a journal’s own, frequently unstable, supplementary-material links.
- Accessible — all three services are free, require no registration, and are reachable through both interactive web interfaces and machine-readable APIs.
- Interoperable — data is served through the shared IVOA protocols and VOTable format described above, rather than a format proprietary to CDS.
- Reusable — VizieR catalogues carry documented provenance back to the originating publication, units and column descriptions are standardized, and cross-identification through SIMBAD lets reused data be checked against everything else known about the same object.
For research administrators supporting astronomy or astrophysics groups, this means CDS’s services are usually the appropriate answer to “where should this dataset be deposited” for object catalogues, tabular survey data, or cross-identification needs, playing a role for astronomy comparable to what the re3data registry and CoreTrustSeal certification do in identifying trustworthy domain repositories more generally, though CDS predates both by decades.
Getting Data Into VizieR: The Journal Submission Pathway
Because much of VizieR’s content arrives through journal-mandated data deposit rather than direct self-service upload, researchers publishing large tables or catalogues in astronomy journals should expect the CDS submission step to be part of the standard publication workflow, coordinated between author, journal, and CDS at the proofing stage, rather than a separate deposit decision made after publication. CDS publishes its own guidance for authors on preparing tables for submission, covering column formatting, units, and machine-readable structure, directly on the VizieR site; researchers preparing a data management plan that names VizieR as a repository should reference that guidance rather than assume generic table formatting will be accepted as-is.
CDS Strasbourg Compared to Other Domain Repositories
CDS’s services are a domain repository in the same sense as other discipline-specific infrastructure CASRAI covers elsewhere: built and governed by subject-matter specialists for one field’s specific data types, rather than serving as a general-purpose institutional or generalist repository. Within astronomy and astrophysics specifically, CDS sits alongside NASA’s NASA Exoplanet Archive (confirmed and candidate exoplanet data) and GWOSC (public gravitational-wave data from LIGO, Virgo, and KAGRA) as one of the field’s principal community repositories, each covering a different slice of the discipline’s data rather than competing for the same data. Compared with domain repositories in other fields, such as NEON in ecology or NOAA NCEI in climate and ocean science, CDS is unusual both in how long it has operated (over five decades) and in how tightly its services are integrated into journal publication workflows rather than sitting downstream of them.
Frequently Asked Questions
Is VizieR the same thing as SIMBAD?
No. SIMBAD identifies astronomical objects and tracks the literature about them; VizieR hosts the actual data tables and catalogues published in that literature. The two are cross-linked but serve different purposes, and a given research task often needs both.
Do CDS services charge for access or require a login?
No. SIMBAD, VizieR, and Aladin are all free to use and do not require account registration for standard access, whether through the web interface or the programmatic, IVOA-standard APIs.
Is CDS Strasbourg the same as “the Virtual Observatory”?
No, though the two are closely related. The Virtual Observatory (VO) is the broader, federated network of astronomical archives and services worldwide, coordinated through IVOA standards. CDS is one, particularly central, participant in that network, and Aladin in particular functions as an access point into VO resources beyond CDS’s own holdings.
How should I cite data pulled from VizieR or SIMBAD in a publication?
CDS provides citation guidance directly on each service’s own site, generally pointing to the original publication associated with a VizieR catalogue plus an acknowledgment of CDS as the service provider. SIMBAD and VizieR are also registered in re3data, a useful reference point when a data management plan needs a formal repository citation. Because citation conventions can change, check the current citation guidance published on the relevant service before finalizing a manuscript or data availability statement.
Related CASRAI resources: FAIR Data Principles, persistent identifiers, CoreTrustSeal certification, and repository.
