The availability and advances in two-dimensional electronic detectors, in particular the charge-coupled-devices (CCDs), are a great asset to astronomical imaging and spectroscopy because of their sensitivity, dynamic range, and linearity. In some cases photographic plates still offer an advantage to imaging of large size, but the advent of large format CCDs may make a figure of merit, the area per exposure time, much more favorable for CCDs.

On the experience acquired since 1983 when creating the Lyon-Meudon Extragalactic Database, we discuss the problems of identifying and designating extragalactic objects. We suggest some ways of improvement. The main conclusion is that it is urgent to use images in a standardised format. The IAU could help to organise such a standardisation.

The “Planetary Data System” (PDS) was developed and supported by the Solar System Exploration Division of the National Aeronautics and Space Administration (NASA) and has now successfully operated for a few years. Its primary objectives are to preserve data obtained from previous, current and future space missions; to help individual scientists in the analysis of planetary data by preparing them in a usable form and making them easily accessible to the community; and to assist the National Space Science Data Center (NSSDC) managing, archiving and distributing data obtained by NASA missions. The principal goals and general structure of the PDS have been summarized in several brochures issued by the PDS and articles such as e.g., “The Planetary Data System” by S.W. Lee, published in the IUGG U.S. National Report on Planetology 1987-1990 or by the Jet Propulsion Laboratory. Additional information can be obtained e.g., by the current author; the PDS Project Manager, S. McMahon at JPL; the PDS Project Scientist, S. Lee at the Laboratory for Atmospheric and Space Physics, University of Colorado or from any of the seven Discipline Nodes listed below.

Current programs which produce asteroid photometric data range from astrometry through visual and near-infrared photometry and spectrophotometry to thermal infrared (8 to 30 micrometers) photometry. These data are published in a variety of places including observatory publications, IAU Circulars, the Minor Planet Circulars, and various journals.

Astronomers have been consciously making positional observations of comets since the sixteenth century, and rough information on bright comets is available from social records collected in the Far East, the Middle East and Europe over the previous two millennia. Attempts at representing the observations with orbits also date back to the sixteenth century, well before the earliest computations were made on the basis of gravitational theory. Improvement in the accuracy of cometary astrometric data was slow to develop following the invention of the telescope and, a few decades later, the micrometer, for this had to await the availability of Flamsteed’s star catalogue and the understanding brought about by Bradley’s discovery of aberration and nutation. In spite of important contributions by some of the most celebrated scientists of the eighteenth century, orbit computation remained largely a process of trial and error until the discovery of the first asteroids and the rise of Gauss and his followers. By the 1880s the availability of a dense star catalogue like the AGK1 was allowing micrometric observations of comets and asteroids often to achieve an accuracy of 2 to 3 arcsec, and the subsequent introduction of photographic astrometry brought convenience but relatively little additional improvement in accuracy. The use nowadays of charge-coupled devices clearly has the potential for a further increase in accuracy, even for diffuse objects like comets, but for the moment the accuracy tends generally to be limited by the inadequacy of the available star catalogues. Modern orbit determination routinely includes the use of sophisticated techniques to identify isolated observations of the same asteroid at different oppositions and in the case of a comet the examination of the nongravitational effects that can strongly influence the object’s motion.

The process of archiving photometric data and compiling catalogues is in principle easy to solve, but, in practice, does not appear so simple. Data retrieval may become difficult and inefficient if sufficient care is not taken to solve the general problems which are encoutered: (i) the lack of definition of fundamental identificators; (ii) the lack of coordinates for thousands of faint stars; (iii) the innacuracy of the identification and description of the components observed in double stars or multiple systems: A, B, C, AB, or BC; (iv) the fact that the number of observations is often not published.

Spectroscopy is a fundamental tool for the investigation of physical conditions in astronomical objects. Up to the present a considerable amount of information has been collected, which could be of great help in research in all fields of Astrophysics. There is however the problem of safeguarding such material, to create ad hoc archives of raw and/or reduced spectral data, and to have homogenised means of documentation and of distribution of the material to the Astronomical Community. These problems were discussed by members of the IAU Commission 29, Stellar Spectra, during the 21st IAU General Assembly, and the results are herewith summarized.

The first question is : which types of data should we archive for variable stars?

Let us consider the three following types of data : (i) raw data (output of the telescope, time…); (ii) reduced data (flux, magnitude…); (iii) processed data (light curve…).

We generally need the third one and use the reduced data only when we have trouble with the processed data or when we could obtain better processed data. We never quite go back to the raw data. The situation could evolve with raw data obtained with the CCD frame where the reduction procedure is more complex than with electronic counts. Then, at first sight, we have first to archive the processed data, then make an effort on reduced data and raw data.

Recent proliferation of large radioastronomical source surveys and resulting data products are reviewed, and attention is drawn to their poor archival status. First practical steps are proposed to establish a radio source data base from published source catalogues, proceeding with time from the bigger and recent ones to the smaller and older ones. At later stages the data base could assimilate unpublished data, spectral-line data and also images.

1. 1. All data generated by HST are preserved in a specially-designed interim archive system, the “Data Management Facility” at ST ScI.

2. 2. Data is currently being written to 2 Gb – 12” optical disks at the rate of about 0.5 Gb/day = 35 exposures/day.

3. 3. A catalog is produced as the data is archived. This catalog is publically accessible and currently contains information on over 19,000 exposures (images, spectra, flat fields, calibration data, etc.)

4. 4. About 14,000 exposures are now non-proprietary; more than a third of these are observations of sky targets obtained during OV/SV.

When considering the archiving of space astronomy data, one has only to look at the current and projected astrophysics missions to be aware of the enormity of the archival requirements and the urgent need for careful planning in order to properly manage all the data which is and will be acquired. The current list of astrophysics missions for which NASA supports observing/archival phases during the next ten years numbers 23! Even when a mission’s observing period was less than a year, as for the Infrared Astronomy Satellite (IRAS), or only a week, as for Astro-1, the archival phases last for many years, especially if the archives are user-friendly and easily accessible.

Astronomy is a natural science based upon observations. Observations are made by somebody at a given time and place, obtained with certain instruments using certain techniques and are interpreted with the help of certain models or theories. The latter may change with time, but observations can be used with any new theory, provided the observational data and the reduction techniques are known.

The problem of optical distortion produced by the earth’s atmosphere has been known in astronomy since Isaac Newton. In 1953 H. W. Babcock (1953) proposed in his paper “The Possibility of Compensating Astronomical Seeing” to use a deformable optical element driven by a wavefront sensor to correct the distortions induced by the atmosphere that affect astronomical imaging. It took another 20 years for this principle to be demonstrated successfully for defence related laser applications. And only in the early eighties the first astronomical adaptive optics projects had been triggered.

There are several ways to use a computer with students for teaching Astronomy. Among many others we can list the following : to emulate and to explain the phenomena as with a planetarium, to visualise some astronomical properties such as the motions in a binary-stars system, or to simulate some observations with a telescope. We shall present here a different approach : the use of a computer to compute and to analyse the content of an astronomical data bank.

The projects developed with the students, in this context, allow them to have access to real astronomical data obtained by professional astronomers and then to make an analysis of the data based on their own knowledge.