Based on the lecture notes of a school titled 'Tides in Astronomy and Astrophysics' that brought together students and researchers, this book focuses on the fundamental theories of tides at different scales of the universe-from tiny satellites to whole galaxies-and on the most recent developments. It also attempts to place the study of tides in a historical perspective. Starting with a general tutorial on tides, the theme of tides is approached in 9 chapters from many directions. They allow non-experts to pick up a physical intuition and a sense of orders of magnitude in the theory of tides. These carefully prepared lecture notes by leaders in the field include many illustrative figures and drawings. Some even offer a variety of simple back-of the-envelope problems.

The ability of storing, managing, and giving access to the huge quantity of data collected by astronomical observatories is one of the major challenges of modern astronomy. At the same time, the growing complexity of data systems implies a change of concepts: the scientist has to manipulate data as well as information. Recent developments of the WorldWideWeb' bring interesting answers to these problems. The book presents a wide selection of databases, archives, data centers, and information systems. Clear and up-to-date descriptions are included, together with their scientific context and motivations. Audience: This volume provides an essential tool for astronomers, librarians, data specialists and computer engineers.

This textbook provides an introduction to the fundamentals of space physics and astrophysics and covers the recent progress in various aspects of these fields. In the introductory Chapter 1, a brief historical account of space research is given, followed by short reviews of the space vehicles used and some aspects of the early years of space research. In Chapter 2, the reader is introduced to the discoveries of the radiation belts and the magnetosphere of the Earth. Chapter 3 begins with the phenomena of the quiet Sun, followed by processes in the active Sun (solar flares, radio bursts and X-ray, gamma-ray and neutron emissions). In Chapters 4 and 5, attention is paid to the physical features and properties of large bodies and aggregates in the matter of the solar system, emphasising discoveries obtained from spacecraft. In Chapter 6 solar energetic particles are presented, bringing out their dual role - as a sample of accelerated matter from the Sun and as a sensitive probe of the interplanetary fields in the heliosphere. Chapter 7 presents a discussion on galactic cosmic rays, explaining the basic features and main findings. Highlights of ultra-high-energy cosmic rays and possible origins are included. Chapter 8 presents exciting results of extreme UV, infra-red, X-rays and gamma-rays from space. These are followed by outlines of the new vistas of cosmological problems as revealed by the cosmic background measurements of X-rays, gamma-rays and microwaves. In Chapter 9, the reader is introduced to the physical and dynamical properties of the interstellar medium. This chapter concludes with the astrophysical aspects of the search for the origin of life. In the concluding Chapter 10 some general trends and future directions are briefly presented. The level of presentation is aimed at senior undergraduate students who are familiar with introductory physics. Graduate students will find more advanced topics discussed through their underlying features. Each chapter is followed by a number of problems; solving these will enable students to obtain a good grasp of the topics.

This volume consists of invited lectures and seminars presented at the NATO Advanced Study Institute "The Infrared and Submillimetre Sky after COBE", which was held at the Centre de Physique Theorique of Les Houches (France) in March 1991. The school has been planned by a Scientific Organizing Committee. It was organized with the aim of providing students and young researchers with an up-to-date account of the Cosmic Microwave Background, the Cosmic Infrared Background (if any), and the infrared emission of the Galaxy, after the early results from COBE (Cosmic Background Explo- rer). It was attended by about sixty researchers from many countries. The lectures and seminars represent a complete coverage of our present knowledge and understanding of: the Early Universe, Large-Scale Structure, Dust in Galaxies, Infrared to Submillimetre Backgrounds, CMB Anisotropies, complementary observations and instrumentation problems, etc. Most of these lectures are reproduced in this volume. Unfortunately, a few lecturers have chosen not to submit their manuscript. I would like to express my gratitude to the Scientific Affairs Division of NATO (North Atlantic Treaty Organization) and to the Theoretical Physics and Astrophysics Sections of the CNRS (Centre National de la Re- cherche Scientifique) for their generous support. Further help was obtain- ed from the DRET (Direction des Recherches, Etudes et Techniques), the CNES (Centre National d'Etudes Spatiales) and the IN2P3 (Institut Natio- nal de Physique Nuc1eaire et de Physique des Particules), which I hereby gratefully acknowledge.

Clusters and superclusters of galaxies are the largest objects in the Universe. They have been the subject of intense observational studies at a variety of wavelengths, from radio to X-ray which has provoked much theoretical debate and advanced our understanding of the recent evolution of the large-scale structure of the Universe. The current status of the subject is reviewed in this volume by active researchers who lectured at a NATO Advanced Study Institute held in Cambridge, England in July 1991. Much of the material is presented in a pedagogical manner and will appeal to scientists, astronomers and graduate students interested in extragalactic astronomy.

ROSAT Observations G. HASINGER Max-Planck-Institut flir extraterrestrische Physik, D-85740 Garching, Germany Abstract. This review describes the most recent advances in the study of the extragalactic soft X-ray background and what we can learn about its constituents. The deepest pointed observations with the ROSAT PSPC are discussed. The logN-logS relation is presented, which reaches to the faintest X-ray fluxes and to the highest AGN surface densities ever achieved. The N(>S) relation shows a 2 density in excess of 400 deg- at the faintest fluxes and a flattening below the Einstein Deep Survey limit. About 60% of the extragalactic background has been resolved in the deepest field. Detailed source spectra and first optical and radio identifications will be discussed. The results are put into perspective of the higher energy X -ray background. Key words: X-rays, background radiations, active galactic nuclei. 1. Introduction The extragalactic X-ray background (XRB), discovered about 30 years ago, has been studied extensively with many X-ray experiments, in particular with the satel lites HEAO I and II (see ego Boldt 1987) and with ROSAT (e. g. Hasinger et aI. , 1993). Figure 1 shows a compilation of some of the most recent spectral measure ments for the X-ray background. Over the energy range from 3 to about 100 keY its spectrum can be well approximated by an optically thin thermal bremsstrahlung model with kT ~ 40 keY, while at lower X-ray energies a steepening into a new component has been observed observed (e. g.

This volume comprises selected lectures presented in the Ninth Course of the International School ofCosmic-Ray Astrophysics held at the Ettore Majorana Centre in Erice, Sicily, May 7-18,1994. Director ofthe Centre is A. Zichichi, assisted by M. Zaini. Director ofthe School is M. M. Shapiro. 1. P. Wefel was co-director of the Ninth Course, which was also a NATO Advanced Study Institute (ASI), and NATO support is gratefully acknowledged. Devoted to problems and prospects in high-energy astrophysics and cosmology, the major areas explored in this course were: gamma-ray, X-ray, and neutrino astronomies; cosmic rays; pulsars and supernova remnants; and cosmology, as well as cosmogony. Among the principal developments in gamma-ray astrophysics were those generated by the Compton Gamma Ray Observatory. Cosmic neutrinos at MeV energies, i.e., those from the sun and from Supernova 1987a, were discussed, as well as neutrino masses in astrophysics. The source composition ofcosmic rays, and extensive air shower experiments, received special attention. The early universe according to COBE data, and as viewed by theorists ofcosmology, was reviewed. Finally, the connections with particle physics occasioned a timely description ofthe Standard Model ofelementary particles.

After a year's successful operation, the European DENIS project is now a scientific reality and its close cousin 2MASS (USA) is about to come into operation. The observational and data reduction processes of both DENIS and 2MASS are fully described in this volume. Already the impact of DENIS is making itself felt in the astronomical community in areas of research as diverse as cosmology, the evolution of galaxies, the interstellar medium, the search for brown dwarfs, and stellar structure and evolution. The first routine results from DENIS and the preliminary results from the 2MASS prototype camera are discussed and compared with other surveys across the wavelength spectrum, both space- and ground-based, including the Digitized Sky Survey, ISO and ROSAT.

An invaluable reference for any student, scientist or administrator, using small telescopes for research. An essential collection of data and opinions for those charged with setting scientific and funding priorities.

This three-volume set, The Future of Small Telescopes in the New Millennium details the essential roles that small telescopes should play in 21st century science and how their future productivity can be maximized. Over 70 experts from all corners of the international astronomical community have created a definitive reference on the present and future of "big science with small telescopes."

Despite highly publicized closures of telescopes smaller than 4-m in aperture at national facilities and their omission from national science priority studies, the oft-lamented demise of the small telescope has been greatly exaggerated. In fact, the future of these workhorses of astronomy will be brighter than ever if creative steps are taken now. This three-volume set defines essential roles that small telescopes should play in 21st century science and the ways in which a productive future for them can be realized. A wide cross-section of the astronomical community has contributed to a definitive assessment of the present and a vision for the future.

Volume 1: Perceptions, Productivities and Policies: - Beginning with a summary of recent national scientific priority-setting efforts, Volume 1 examines the public's and the astronomical communities' own perceptions and misconceptions of small telescope productivity. These shape the future scientific research that will be done with telescopes smaller than 4-m in aperture and the number of astronomers that will have access to them.

Volume 2: The Telescopes We Use: - Small cost-effective optical-, radio- and space-based facilities face similar problems in scientific prioritization and funding. Volume 2 highlights how current small facilities are evolving to meet the scientific priorities and economical realities of the 21st century through standardization of instrumentation, use of off-the-shelf technology, specialization, optical improvements, new modes of scheduling, automation, and internet access.

Volume 3: Science in the Shadow of Giants: - What first-rank science can small telescopes contribute in the coming era of 30-m class giant telescopes? Volume 3 explores a broad selection of scientific initiatives, from planetary astronomy to cosmology, that are ideally suited for small telescopes.

The Future of Small Telescopes in the New Millennium is a fundamental resource for those looking to undertake new projects with small telescopes, for those that are responsible for their operation, and for those called upon to help set scientific priorities for the coming decade. It will be useful for the practicing researcher, mountain facility manager, science policy maker, and beginning graduate student.

Telescopes and Techniques has proved itself in its first edition, having become probably one of the most widely used astronomy texts, both for numerate amateur astronomers and for astronomy and astrophysics undergraduates. The first and second editions of the book were widely used as set texts for introductory practical astronomy courses in many universities.
This book guides the reader through the mathematics, physics and practical techniques needed to use telescopes (from small amateur models to the larger instruments installed in many colleges) and to observe objects in the sky. Mathematics to around Advanced Placement standard (US) or A level (UK) is assumed, although High School Diploma (US) or GCSE-level (UK) mathematics plus some basic trigonometry will suffice most of the time. Most of the physics and engineering involved is described fully and requires no prior knowledge or experience.
This is a how to book that provides the knowledge and background required to understand how and why telescopes work. Equipped with the techniques discussed in this book, the observer will be able to operate with confidence his or her telescope and to optimize its performance for a particular purpose. In principle the observer could calculate his or her own predictions of planetary positions (ephemerides), but more realistically the observer will be able to understand the published data lists properly instead of just treating them as recipes. When the observer has obtained measurements, he/she will be able to analyze them in a scientific manner and to understand the significance and meaning of the results.
Telescopes and Techniques, 3rd Edition fills a niche at the start of an undergraduate astronomer s university studies, as shown by it having been widely adopted as a set textbook. This third edition is now needed to update its material with the many new observing developments and study areas that have come into prominence since it was published. The book concentrates on the knowledge needed to understand how small(ish) optical telescopes function, their main designs and how to set them up, plus introducing the reader to the many ways in which objects in the sky change their positions and how they may be observed. Both visual and electronic imaging techniques are covered, together with an introduction to how data (measurements) should be processed and analyzed. A simple introduction to radio telescopes is also included. Brief coverage of the most advanced topics of photometry and spectroscopy are included, but mainly to enable the reader to see some of the developments possible from the basic observing techniques covered in the main parts of the book."

We are well aware of how dust influences our observations of distant stars and how easily dust may mislead us with regard to the way in which stars are distributed within the Galaxy, but how does dust affect our view of other galaxies? This is the question that was posed to those who attended this meeting. By its very nature dust is illusive: as dust obscures by both scattering and absorption, it can effectively disguise its very own existence. It was not until the mid-1930's that astronomers generally agreed that dust did redden and dim stars in our own Galaxy, and it was not until the late 1950's that astronomers began to seriously inquire of its effects in other galaxies To the best of our knowledge, this is the first international meeting to have been held devoted solely towards understanding the observational effects of dust in other galaxies. Because of this we have been fortunate in attracting many of the major workers in this field, both observers and theorists. Among these pages the reader will find a wide range of opinion about how much dust there is in the disks of galaxies, where that dust is, and how to model the effects of dust. We tried to structure this meeting so that there was a ready and easy exchange between the speaker and the audience, and so that there was a large amount of time for discussion.

The Olympia conference Frontiers of Fundamental Physics was a gathering of about hundred scientists who carryon their research in conceptually important areas of physical science (they do "fundamental physics"). Most of them were physicists, but also historians and philosophers of science were well represented. An important fraction of the participants could be considered "heretical" because they disagreed with the validity of one or several fundamental assumptions of modern physics. Common to all participants was an excellent scientific level coupled with a remarkable intellectual honesty: we are proud to present to the readers this certainly unique book. Alternative ways of considering fundamental matters should of course be vitally important for the progress of science, unless one wanted to admit that physics at the end of the XXth century has already obtained the final truth, a very unlikely possibility even if one accepted the doubtful idea of the existence of a "final" truth. The merits of the Olympia conference should therefore not be judged a priori in a positive or in a negative way depending on one's refusal or acceptance, respectively, but considered after reading the actual of basic principles of contemporary science, new proposals and evidences there presented. They seem very important to us.

One service mathematics has rmdcred the 'Et moi, .*.* si j'avait su comment en rcvenir. human race. It has put common sense back je n'y semis point aile.' whc:rc it belongs, on the topmost shcIl next Jules Verne to the dusty callister labc:1lcd 'discarded non- sense'. The series is divergent; thererore we may be Eric T. Bell able to do something with iL O. Hcavisidc Mathematics is a tool for thought. A highly necessary tool in a world where both feedback and non- linearities abound. Similarly, all kinds of parts of mathematics serve as tools for other parts and for other sciences. Applying a simple rewriting rule to the quote on the right above one finds such statements as: 'One service topology has rendered mathematical physics ...'; 'One service logic has rendered com- puter science ...'; 'One service category theory has rendered mathematics ...'. All arguably true. And alI statements obtainable this way form part of the raison d'etre of this series.

In this book are reported the main results presented at the "Fourth International Workshop on Data Analysis in Astronomy," held at the Ettore Majorana Center for Scientific Culture, Erice, Sicily, Italy, on April 12-19, 1991. The Workshop was preceded by three workshops on the same subject held in Erice in 1984, 1986 and 1988. The frrst workshop (Erice 1984) was dominated by presentations of "Systems for Data Analysis"; the main systems proposed were MIDAS, AlPS, RIAIP, and SAIA. Methodologies and image analysis topics were also presented with the emphasis on cluster analysis, multivariate analysis, bootstrap methods, time analysis, periodicity, 2D photometry, spectrometry, and data compression. A general presentation on "Parallel Processing" was made which encompassed new architectures, data structures and languages. The second workshop (Erice 1986) reviewed the "Data Handling Systems" planned for large major satellites and ground experiments (VLA, HST, ROSAT, COMPASS-COMPTEL). Data analysis methods applied to physical interpretation were mainly considered (cluster photometry, astronomical optical data compression, cluster analysis for pulsar light curves, coded aperture imaging). New parallel and vectorial machines were presented (cellular machines, PAPIA-machine, MPP-machine, vector computers in astronomy). Contributions in the field of artificial intelligence and planned applications to astronomy were also considered (expert systems, artificial intelligence in computer vision).

The NATO Advanced Study Institute "Cosmological Aspects of X-Ray Clus ters of Galaxies" took place in Vel en, Westphalia, Germany, from June 6 to June 18, 1993. It addressed the fruitful union of two topics, cosmology and X-ray clus ters, both of which carry substantial scientific weight at the beginning of the last decenium of the last century in the second millenium of our era. The so far largest X-ray "All-Sky Survey," observed by the ROSAT X-ray satel lite, and ROSAT's deep pointed observations, have considerably enlarged the base of X-ray astronomy, particularly concerning extragalactic sources. Cosmology has gained significant impetus from the large optical direct and spectroscopic surveys, based on high quality 2-dimensional receivers at large telescopes and powerful scan ning devices, harvesting the full information 1 content from the older technique of employing photographic plates. Radioastronomy and IR-astronomy with IRAS, as well as r-astronomy with GRO, continue and strengthen the role of extragalactic research. The rapidly growing computer power in data reduction and data storage facilities support the evolution towards large-number statistics. A most significant push was given to early cosmology by the needs of physics in trying to unravel the nature of forces which govern our material world. The topic of the ASI was chosen because it opens new vistas on this for ever new problem: the universe. Clusters of galaxies probe large-scale matter distributions and the structure of space-time."

Accretion disks in astrophysics represent the characteristic flow by which compact bodies accrete mass from their environment. Their intrinsically high luminosity, and recent progress in observational accessibility at all wavelength bands, have led to rapidly growing awareness of their importance and made them the object of intense research on widely different scales, ranging from binary stars to young stellar objects and active galactic nuclei. This book contains the proceedings of the NATO Advanced Workshop on `Theory of Accretion Disks 2' for which some of the most active researchers in the different fields came together at the Max-Planck-Institut for Astrophysics in Garching in March, 1993. Its reviews and contributions give an up-to-date account of the present status of our understanding and provide a stimulating challenge in discussions of open questions in a rapidly developing field.

Otto von Guericke has been called a neglected genius, overlooked by most modern scholars, scientists, and laymen. He wrote his Experimenta Nova in the seventeenth century in Latin, a dead language for the most part inaccessible to contemporary scientists. Thus isolated by the remoteness of his time and his means of communication, von Guericke has for many years been denied the recognition he deserves in the English speaking world. Indeed, the century in which he lived witnessed the invention of six important and valuable scientific instruments -- the microscope, the telescope, the pendulum clock, the barometer, the thermometer, and the air pump. Von Guericke was associated with the development of the last three of these; he also experimented with a rudimentary electric machine. Thus his Experimenta Nova was an important work, heralding the emerging empiricism of seventeenth century science, and merits this first English translation of von Guericke's magnus opus.

The study of white dwarfs has been steadily growing during the last years and now is a mature field extending its influence over many others. Since white dwarfs are long lived objects, they can be used to obtain information about the history of the Galaxy. The simplicity of their structures enables them to act as precise particle physics laboratories and the extreme con ditions reached at their surfaces allow us to test the equation of state and to study the behavior of matter under conditions impossible to be reached in terrestrial laboratories. Nevertheless, white dwarfs are still challenging astrophysicists. Many questions, ranging from the determination of funda mental parameters to the evolution of their outer layers, are still waiting for a satisfactory answer. The European Workshop series on White Dwarfs started in 1974 as a con sequence of the effort and enthusiasm of Professor Volker Weidemann. The existing proceedings of these meetings, together with those corresponding to the lAU Colloquia held in Rochester (1979) and in Hanover (1988), provide a unique opportunity to follow the development of this field. We hope that the present volume will provide a representative snapshot of the state of the art in 1996. In this sense we are very indebted to all the participants that have sent their contributions according to the instructions (this clearly excludes everybody beyond three sigmas from the standards).

I have been asked by Professor Kikuchi to write a foreword for this interesting book on Dusty Plasmas and other electrical phenomena. This was a somewhat daunting task due to the wide range of topics covered. In what follows I have attempted to summarize most of these topics; for this purpose I have divided them into four groups, namely (a) Dusty Plasmas, (b) The Electrical Environment, (c) Lightning and (d) The Noise Environment. I hope that I have succeeded. in indicating that each section contains much that is of great interest. It is perhaps unnecessary for me to point out that the book contains subjects which are at an exciting and important stage in their development. (a) Dusty Plasmas The subject of dusty plasmas is one of great interest. Dust particles in interplanetary space, within comets, in inter-stellar space and at ever greater distances will in general be charged. The plasma environment will ensure this, bombarding electrons will charge up the particle until it assumes a "floating potential," although time variation can occur. Ultra violet radiation can cause photoemission and in certain cases field emission is a possibility. The motion of the particles will be determined by electric and magnetic fields together with gravity. If the density of charged grains becomes sufficiently high the grains will interact with each other and collective behaviour will ensue. This newly evolving subject entails the study of all kinds of plasma waves.

This book reports the Proceedings of the NATO Advanced Research Workshop on "An gular Momentum Evolution of Young Stars" held from 17 to 21 September 1990 at Noto, Italy. The workshop had its immediate origin in a discussion about the availability of stel lar rotation data, that took place in 1987 at Viana do Castelo Portugal during the NATO meeting, Formation and Evolution of Low Mass Stars. We recognized that nearly 20 years had passed since the last meeting on stellar rotation and that significant progress in the observation of rotation rates in low mass stars had been made. During the last 20 years, new efficient instrumentation (CCD and photon counting de tectors and echelle spectrographs) and new analysis techniques (profile Fourier analysis) have allowed us to measure rotational velocities as low as 1-2 km/s and to reach low mass stars in young clusters. Even with these advances, rotational velocities of low mass stars would have remained challenging to determine if all single, low mass stars later than GO had rotational velocities of order or less than 10 km/sec. Evidence that this is not always the case was first provided by the photometric variability data obtained by van Leeuwen and Alphenaar for K dwarfs in the Pleiades and more recently by the vsini measurements of low mass stars in several young clusters."

The past year has produced some of the most exciting results in the history of astronomy, particularly in the area of planets outside our solar system. Only a half-year before our meeting in Toledo, Spain, the first unambiguous detection of planet-sized masses orbiting main sequence stars were reported. Since that time, evidence for a new exo planet has been reported almost at the rate of about once per month. Some of these objects are likely to turn out to be very low-mass stars, but something like half show characteristics - Jupiter-like mass and near-zero orbital eccentricity - which appear to be unique to planets. Almost at the same time that giant planets were being discovered regularly, the two major space agencies, ESA and NASA, have iden tified searches for and detailed study of Earth-like planets as a major priority for the future. In ESA's "Horizon 2000 Plus" programme, an infrared interferometer has been proposed as a possible future Cor nerstone mission. Similarly, scientists in the US produced the "Road Map for the Exploration of Neighboring Planetary Systems (ExNPS)", which provided NASA with a long-term plan which leads also to an infrared interferometer in space to study hypothetical Earth-like worlds beyond our Solar System. Such an observatory is designed to search for the thermal emission from a family of planets, using interferometric nulling to remove the contaminating light from the central star.

Editing the proceedings of a scientific meeting is not an easy task. Sometimes people who give an excellent talk do not send the manuscript by the deadline. However, this time, thanks to the punctuality of all the participants, we have this excellent volume for the workshop on mass losing pulsating stars and their circumstellar matter prepared in time. Almost all of the oral presentations including the summary are collected in this volume. We regret that we cannot put in this volume a few posters that we failed to receive before the editorial work. The workshop was planned as a small meeting with less than fifty attendants because the city of Sendai was far from the most of the active institutions. However, the number of submitted papers exceeded the SOC's expectation; many interesting contributions had to be scheduled in the poster session. Still, the oral sessions were so tight that many participants might have felt frustrated for the shortage of discussions. The organizers of the workshop have to apologize to the attendants for the inconvenience caused from such a happy underestimate about the size of the workshop.

Freja is a joint Swedish and German satellite, launched on October 6, 1992 and orbiting at 600--1750 km, covering the lower part of the auroral acceleration region. It has been designed to provide high-resolution measurements (both temporal and spatial) of auroral plasma characteristics. The high telemetry rate, together with the 15 Mbyte distributed on-board memories allow Freja to resolve meso and micro-scale phenomena in the 100 m range for particles and 1--10 m range for electric and magnetic fields. The UV imager resolves auroral structures of 1 km size at a time resolution of one image every 6 s. The novel plasma instruments are orders of magnitude better than any that have gone before. The Freja Mission is about the scientific objectives, instruments and platform itself. Detailed descriptions are given of the instrumentation and the first data acquired. It is one of the very few books to contain such material in a single volume, relating the instruments' design with their in-flight characteristics. For space engineers and other researchers interested in space science.

E. KONTIZAS Astronomical Institute National Observatory of Athens P. O. Box 20048 Athens GR-1181O GREECE The international conference on "Wide-Field Spectroscopy" and its sub ject matter were agreed during the general assembly of the International Astronomical Union (IAU) in August 1994 by the Working Group of Com mision 9 "Wi de-Field Imaging". This meeting gave an opportunity to world experts on this subject to gather in Athens, in order to discuss the cur rent exploitation and the impending opportunities that exist in the area of multi-object spectroscopy, with particular emphasis on: 1. Astronomical instruments, data acquisition, processing and analysis techniques. 2. Astrophysical problems best tackled through wide-field, multi-object spectroscopy. The new fibre optic technology offers an important tool for the advancement of basic research and the development of industrial applications. Astronom ical spectroscopy is a field of astronomy which has contributed much to the advancement of fundamental physics. The spectra of hot stars have been used to determine the well-known Balmer formula for the wavelength of hydrogen lines, in the late 19th century. Since then, spectroscopy has made enormous progress in stellar atmosphere studies, in kinematics, and in the detection of high redshifts in the Universe. The traditional techniques of obtaining wide-field spectroscopic data are based on slitless spectroscopy (objective prism). Several observations, world wide, make use ofthese tech niques in order to obtain information on the spectral properties of objects in large areas of the sky.