Astronomy Online

Astronomical Data Archives


Many astronomical observatories and institutes have important data archives which contain large amounts of information.

Some archives date back to earlier centuries and consist for example of notebooks kept by astronomers during their observations. Others take the form of collections of photographic plates, many from the first half of the 20th century and carefully stored in special rooms where they may be consulted by today's astronomers.

Nowadays, most archives are kept in electronic form and information may therefore be retrieved via a computer. Several observatories have made their archives public, that is, they can be accessed from the outside, via the World-Wide-Web.

This page contains information about some of these archives and the corresponding links. From here you will therefore be able to enter some of the world's foremost astronomical databanks and retrieve information which you can use for your own purpose.

However, before you start, you must be aware that sometimes these data are protected by copyright. That means that you may not use them for any commercial purpose and you may not publish them, before you have received permission from the institute that is responsible for the data bank. In most cases, there will be an indication about how this is administered.

Nevertheless, data which is retrieved from these sites by Astronomy On-Line participants may be freely used within this Programme. In particular, you are welcome to include them in your report which will be submitted at the end of this Programme and published in the Newspaper, provided you are careful to indicate form where you have obtained the data on which your work is based.

We wish you an enjoyable tour through the labyrints!

How to find the archives

In order to improve research facilities and their efficiency astronomical data, e.g. images, spectra, catalogues, are offered to the community by several, mostly larger, institutions. At ESO, an overview of these data archives can be found at URL: As you quickly see the amount of archives and catalogues that is available on-line is huge, and still growing daily by several gigabytes. More archives are listed in

For most databases, scientists and educators may freely use these data for research, teaching purposes and other non-profit activities, and the only request is that you acknowledge the source in any publication. Commercial use of these data is prohibited without permission. In order not to get drowned by the overwhelming quantity we only present two useful catalogue that may be of use for the participants of the Astronomy On-Line Program. Note, be aware that retrieval of data using one of the available databases may take a moment if the networks are busy, so please be patient.

At ESO, most of the archives and databases are accessed by the special interface, WDB, that provides simple ways for requesting the information. If you intend to use on of the data bases provided, the following URL may be of interest for using the graphics user interface for that particular database:


ESO NTT Archive Query Form

The ESO Archive Database contains all observations performed with the ESO NTT telescope and EMMI/SUSI since April 1, 1991. The observations themselves are kept in an off-line archive and have, each, a proprietary period to the original observer of one year. Data sets can be requested after this period by the general astronomical community. Images and spectra are stored in the archive in unreduced (raw) form in adition to Calibration and auxiliary data.

The search in the database can be useful to see of one or more of the object you are interested in have been observed already, and its data could be requested. The selection can to be done using the areas "Target Information", "Proposal Information", or "Observation Parameters". Simple dis/enable the buttons in front of the various fields and click on thr search button for executing the query.

To request off-line datasets please mark the datasets in the results table by checking the box at the left-most column, then press the button labeled Request Marked Datasets (to do this you will need to provide an archive username and password. If you are not yet registered as an archive user you can fill out the registration form).


In the area "Proposal Information" set the Observer button on and type "West". In the "Target Information area" switch on the Ra field and fill it with "19 39 04.8". Similarly, switch the Dec field and fill it with "-20 26 44.2". Finally, in the area "Observation Parameters" switch on the "Exp. Type....." and fill it with "SCI". Then click on "Search". The resuls is a nice list observations (12) of the comet Hale-Bopp.

ESO Online STScI Digitized Sky Survey

The Digitized Sky Surveys (DSS) is produced by the Space Telescope Science Institute of the Hubble Space Telescope through its Guide Star Survey (see below) group. The on-line Digitized Sky Surveys (DSS1 & 2) server at the ESO/ST-ECF Archive provides access to data stored on CD-ROM set. DSS1 data with declination lower than + 24 degrees is stored onmagnetic disks. DSS1 data with declination higher than 24 degrees and DSS2 is stored on CD-ROM in a Juke Box. To retrieve data from this server you can use URL:,

that gives you simple form to fill out.

To get an image from the Digitized Sky Survey, you will need the right ascension and declination of the area you're interested in (fields Coordinates). However, if all you know is the name of an object (field Object Name) you still will be able to retrieve your image. In that case, the coordinates will be resolved by the SIMBAD database in Strasbourg that contains comprehensive lists of all kinds of objects from all the major astronomical catalogs. The image size (field Image Size) may be useful to specify in order to reduce transfer time. The field survey can be specify for indicating from which one of the surveys the data should be retrieved from.

The output images can be delivered in several formats (field Output Format). The most common ones are: FITS, the standard Astronomical format for data exchange, and GIF. Further more in the field you can choose to display the images directly instead of first saving them to disk. This second option is of use to inspect the image first, prior to downloading, which in the case of large images can be time consuming.


   Coordinates:     blank (R.A.)  blank (Dec.)
   Object Name:     NGC 4321
   Image Size:      5  X (arcminutes)    5  Y (arcminutes) 
   Survey:          DSS-1 (entirely available)
   Output format:   Download as FITS file

and thereafter I have clicked the Retrieve image button. First I got a panel with default name and directory for the output image (which I didn't change). After a click in this panel is got what I wanted: the file dss.

Other useful information that can be obtained:

   FAQ (Frequently asked Questions):
   The STScI User's Guide:
   Other versions of DSS:  

ESO HST Guide Star Catalogue

The Guide Star Catalog (GSC), which has been constructed to support the operational need of the Hubble Space Telescope (HST) for off-axis guide stars, contains nearly 19 million objects brighter than sixteenth magnitude, of which more than 15 million are classified as stars. The Online HST Guide Star Catalogue (GSC) Server at the ESO/ST-ECF Archive provides access to the all-sky astrometric and photometric catalogue from the set of two CD-ROMs produced by the Space Telescope Science Institute.

To retrieve data from this server you can use URL:,

that gives you a simple form to fill out. The input is very similar to that for the DSS form. Additional fields are for define the search area (Search Radius), the magnitude range (Magnitude Limit), and for sorting (Sort Output). Other fields can be used to reduce the output.

Other useful information that can be obtained:

   The Guide Star Catalog v1.1:
   Guide Star Catalogue Information:
   FAQ (Frequently asked Questions):

Author: Rein Warmels (ESO).

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