UV astronomy throughout the ages: a historical perspective

Astronomers have long recognized the critical need for ultraviolet imaging, photometry and spectroscopy of stars, planets, and galaxies, but this need could not be satisfied without access to space and the development of efficient instrumentation. When UV measurements became feasible, first with rockets and then with satellites, major discoveries came rapidly. It is true in the UV spectral region as in all others, that significant increases in sensitivity, spectral resolution, and time domain coverage have led to significant new understanding of astrophysical phenomena. I will describe a selection of these discoveries made in each of three eras: (1) the early history of rocket instrumentation and Copernicus, the first UV satellite, (2) the discovery phase pioneered by the IUE, FUSE and EUVE satellites, and (3) the full flowering of UV astronomy with the successful operation of HST and its many instruments. I will also mention a few areas where future UV instrumentation could lead to new discoveries. This review concentrates on developments in stellar and interstellar UV spectroscopy; the major discoveries in galactic, extragalactic, and solar system research are beyond the scope of this review. The important topic of UV technologies and detectors, which enable the remarkable advances in UV astronomy are also not included in this review.     

An imaging optical/UV monitor for X-ray astronomy observatories

The understanding of high-energy astrophysical sources often depends on observations over the entire electromagnetic spectrum. Yet, extensive multifrequency observing campaigns can consume the resources of a large number of telescopes, including ground-based and satellite facilities, and usually involve large, unwieldy consortia of observers. Because most X-ray sources are variable on a short time-scale, there is an additional need to make the multifrequency observations simultaneous. The logistical difficulties involved in coordinating these observations, coupled with the vagaries of the weather at ground-based observing sites, mean that comparatively few such coordinated campaigns are attempted; of those that have been tried the success rate for achieving simultaneity is low.In the present paper we argue that simultaneous X-ray, optical and ultraviolet observations could be achieved more logically, cheaply, and effectively by mounting a small boresighted optical/UV-telescope alongside future X-ray telescopes. A 12 optical/UV monitor could, for instance, be incorporated into X-ray facilities such as the American AXAF or the European XMM missions with minimal impact on the total cost, weight, size, and telemetry requirements. Such a telescope, equipped with a position sensitive photoncounting detector, could provide two-dimensional photometric imaging of stars as faint asB=23.5 in a 1000 s exposure with a resolution that could easily be matched to that of the X-ray telescope. A series of wide- and narrow-band filters could be used to define spectral bands, while wide-field, low-resolution spectroscopy could be provided by a prism. Such an instrument could monitor not only the multifrequency variability of such active sources as quasars, Seyfert galaxies, BL Lac objects, X-ray binaries, cataclysmic variables, RS CVn stars, and flare stars, but also could provide astrometry, broadband colours, low-resolution spectroscopy, and imaging of constant sources and fortuitously observed field objects. Moreover, the concept of providing multifrequency simultaneous coverage of astrophysical objects in an unbiased way allows new phenomena to be discovered. A review is given of the scientific problems that require such a monitor, and some of the design and performance characteristics of a suitable monitor are discussed.     

New progress on the Fresnel imager for UV space astronomy

We propose a next generation space instrument: the Fresnel imager, a large aperture and lightweight focusing device for UV astrophysics. This paper presents the laboratory setup used to validate the Fresnel imager at UV at wavelengths around 260 nm, and the results obtained. The validation of this optical concept in the visible domain has been previously published, with the first results on sky objects. In this paper we present new optical tests in the UV, of diffractive focusing and chromatic correction at wavelengths around 260 nm. The results show images free from chromatic aberration, thanks to a chromatic corrector scheme similar to the one used in the visible. To complete these tests and reach real astrophysical UV sources, we propose a short space mission featuring a Fresnel imager prototype placed on the international space station: during the mission this small aperture instrument would be aimed at UV sources such as bright stars and solar system objects, to assess at relatively low cost the limits in contrast and resolution of diffractive focusing in space conditions, on real UV astrophysical objects. At wavelengths from 100 to 300 nm, covering Lyman-α, we expect some scientific return from this mission, but the main goal is to increase the TRL, improving the chances of success for a later proposal featuring a full fledged Fresnel imager 10 meters in aperture or more, that would explore new domains of UV astrophysics at very high angular resolution and very high contrast.     

How the space astronomy has extended the horizon of astronomy

On the basis of my experience in the X-ray astronomy, and on some typical highlights of multi-wavelength observations, I emphasize the importance of collaboration between space astronomy and ground-based astronomy.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

Thread safe astronomy

Observational astronomy is the beneficiary of an ancient chain of apprenticeship. Kepler's laws required Tycho's data. As the pace of discoveries has increased over the centuries, so has the cadence of tutelage (literally, “watching over”). Naked eye astronomy is thousands of years old, the telescope hundreds, digital imaging a few decades, but today's undergraduates will use instrumentation yet unbuilt – and thus, unfamiliar to their professors – to complete their doctoral dissertations. Not only has the quickening cadence of astronomical data‐taking overrun the apprehension of the science within, but the contingent pace of experimental design threatens our capacity to learn new techniques and apply them productively. Virtual technologies are necessary to accelerate our human processes of perception and comprehension to keep up with astronomical instrumentation and pipelined dataflows. Necessary, but not sufficient. Computers can confuse us as efficiently as they illuminate. Rather, as with neural pathways evolved to meet competitive ecological challenges, astronomical software and data must become organized into ever more coherent ‘threads’ of execution. These are the same threaded constructs as understood by computer science. No datum is an island. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TeV gamma-ray astronomy

The field of ground-based gamma-ray astronomy has enjoyed rapid growth in recent years. As an increasing number of sources are detected at TeV energies, the field has matured and become a viable branch of modern astronomy. Lying at the uppermost end of the electromagnetic rainbow, TeV photons are always preciously few in number but carry essential information about the particle acceleration and radiative processes involved in extreme astronomical settings. Together with observations at longer wavelengths, TeV gamma-ray observations have drastically improved our view of the universe. In this re- view, we briefly describe recent progress in the field. We will conclude by providing a personal perspective on the future of the field, in particular, on the significant roles that China could play in advancing this young but exciting field.     

On post-SKA radio astronomy

It is suggested that the development of the SKA will drastically change the face of radio astronomy in the 21st Century. A FAST-style SKA would admit observations of low contrast features, and would be the best design for studying the `dark ages' of the Universe (x≫ 1) where sub-arcmin total power instruments can usefully be employed. To date there have been no proposals for post-SKA, billion square-metra instruments; we speculate that mobile communication systems can be used. In the very distant future, SKA multi-beam systems could be used to collect signals reflected by Solar system bodies such as the asteroid belt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Space astronomy in Japan

Japan's two X-ray astronomy satellites, HAKUCHO and TENMA, have been actively in operation leading to deeper understandings of the neutron star physics. Other satellite and balloon projects have been performed under international collaborators.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Early Cambridge radio astronomy

Radio astronomy started in Cambridge immediately after the hostilities of the World War II have ceased. Martin Ryle was the inspiring leader of a small group that started to develop interferometry techniques at the Cavendish Laboratory. From this development came the numerous Cambridge radio source surveys culminating in the Nobel prize awarded to Martin Ryle for invention of aperture synthesis. The history of this early development is the subject of the present paper. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Metallic particles in astronomy

We discuss some implications of iron whiskers condensing in supernova ejecta and being expelled into interstellar and intergalactic space. The supposition that the universal microwave background is a relic from an early hot state of the Universe is shown to be not as secure as is commonly supposed.     

Early history space astronomy

The history of space astronomy is usually written from the perspective of the remarkable scientific findings garnered by space astronomers and the ways these findings have enriched and guided new views of the universe. This paper examines some aspects of the history of space astronomy in the early years of NASA, but takes patronage, management and control as its key issues.     

Multiple-mirror telescope systems in astronomy

The function of a telescope is to optimize the transfer of the information of interest from a source of finite angular size to the analytical device which is going to extract it. It is far from obvious that the conventional large telescope is the optimum fore-optical system for looking through a turbulent atmosphere. There are considerable scientific and financial advantages in going to multiple-imaging-elements and several groups in different parts of the world are working in this direction.Presented at Primars-1 Conference, held at University of Manchester, June 26–30, 1979.     

Amateur astronomy in South Africa

A review is given of the achievements of amateur astronomers in South Africa.     

The development of radio astronomy

Following the detection of extraterrestrial radio waves in 1932 by Karl Jansky, radio astronomy developed quickly after World War II. It established itself soon as a new branch of astronomy with today's outstanding record in the detection of new phenomena in space. These have been honoured by a number of Nobel prizes. Radio astronomy largely depends on technical developments in receiver technology, antenna systems, electronics and computing power. Ever shorter wavelengths down to the submm‐wavelength range became accessible, resulting in new exciting discoveries. However, now and in future care must be taken, in particular for the lower frequency range, of harmful man‐made interferences, which might mask the weak signals from space. New international facilities with orders‐of‐magnitude higher sensitivity like ALMA and SKA are planned or under construction. Space‐borne observatories like PLANCK will detect weak fluctuations of the cosmic microwave background, which will constrain cosmological models with an unprecedented accuracy.