Welcome to astrophotography! This book is for people who want to take pictures of the stars and planets, and, perhaps more importantly, who want to understand how astrophotography works. The earlier chapters contain instructions for beginners, and the later chapters are more like a reference book.

My goal is to show you how to do astrophotography at modest cost, with the equipment and materials an amateur can easily obtain and use. I haven't covered everything. I've concentrated on 35-mm cameras and relatively inexpensive telescopes, 20-cm (8-inch) and smaller. Techniques that require unusual skill or expenditure are mentioned only briefly with references to other sources of information.

The challenge of astrophotography

Why photograph the sky? Because of the great natural beauty of celestial objects, because your pictures can have scientific value, and, perhaps most importantly, because you enjoy the technical challenge. Astrophotography will never be a matter of just taking snapshots, and Kodak's old slogan, “You press the button, we do the rest,” certainly doesn't apply. Astrophotographers push the limits of their equipment and materials, and a good astrophotographer has to know optics and film the way a race-car driver knows engines. There are three main technical challenges:

• Most celestial objects require magnification; that's one reason we use telescopes. (Not all objects require magnification; star fields, meteors, and bright comets can be photographed with your camera's normal lens.)

• Many celestial objects are faint, requiring long exposures to accumulate light on the film. In fact, astronomical discoveries have been made this way; the Horsehead Nebula and Barnard's Loop are too faint to see with any telescope, but are not too hard to photograph.

• […]

The following pages are excerpts from film data booklets, reproduced by permission of Eastman Kodak Company. The films covered are:

1. • Kodak Technical Pan Film (black-and-white)

2. • Kodak Professional Ektachrome Film E200 (color slides)

3. • Kodak Professional Ektapress Films (color negatives)

To save space, some information not relevant to astrophotography has been left out. Complete, up-to-date data booklets are available from Kodak and other film manufacturers.

Because products change frequently, you should always use the most current information. These data sheets will remain useful as a basis of comparison for evaluating newer products.

Kodak Technical Pan Film (TP)

From Kodak Publication P-255, June, 1996. Copyright © 1996 Eastman Kodak Company

DESCRIPTION

KODAK Technical Pan Film is Kodak's slowest and finest-grained black-and-white film for pictorial photography (when developed in KODAK TECHNIDOL Liquid Developer). It is a variable-contrast panchromatic film with extended red sensitivity; because of its extended red sensitivity, it yields prints with a gray-tone rendering slightly different from that produced by other panchromatic films. (This is most noticeable in portraits, in which it suppresses blemishes.)

Use this film for pictorial, scientific, technical, and reversal-processing applications. It is an excellent choice for making big enlargements or murals.

APPLICATIONS

You can vary the contrast of KODAK Technical Pan Film by modifying development. The wide range of contrast levels, along with the spectral sensitization and combination of speed and image-structure properties, makes this film unusually versatile and suitable for many applications:

1. • Pictorial photography

2. • Photomicrography

3. • Microphotography (Microfilming)

4. […]

Amateur high-resolution photography of the sun, moon, and planets is a neglected field. I must confess to having neglected it myself, favoring wide-field deep-sky work like so many other amateurs. But high-resolution solar-system photography has several attractions. You can do it in town or even in a large city; you don't have to go elsewhere in search of dark skies. You don't have to wait for the moon to get out of the way; in fact, the moon is one of the targets. Perhaps more importantly, the appearance of the sun and many of the planets is constantly changing, so it's worthwhile to keep photographing the same object; the pictures stand a good chance of having scientific value.

With the advent of digital image enhancement – which often improves planetary pictures dramatically – and the publication of excellent handbooks by Dobbins, Parker, and Capen (1988) and Dragesco (1995), interest in the solar system may be reviving. This chapter will tell you how to get started with this rewarding kind of work.

Film or CCD?

The advent of CCD imaging has made it easier than ever for amateurs to obtain excellent images of the sun, moon, and planets. My first CCD image of Jupiter, taken with an 8-inch telescope, surpassed all my earlier photographs. There are several reasons for this. Unlike a conventional camera, a CCD does not produce any shutter vibration.

Introduction: the energy problem

The discovery of quasi-stellar objects (QSOs or quasars) in 1963 represents a landmark in observational astronomy. Thanks to a coordination between optical and radio astronomers, it was possible to discover a new and important class of astronomical objects. Because this text book is all about quasars and related phenomena, it will not be out of place to begin at the beginning of the subject and to review briefly how these remarkable objects were first discovered.

The science of radio astronomy really began after the end of World War II, when some of the scientists and engineers engaged in wartime radar projects used their know-how to follow up the pioneering works of Karl Jansky in the 1930s and Grote Reber in the early 1940s. Thus radio dishes and interferometers appeared in England and Australia, at Jodrell Bank, Cambridge, Sydney and Parkes.

The early observations revealed the existence of cosmic radio sources and by the mid- 1950s it became an accepted fact that radio galaxies exist. The nature of their radiation was non-thermal, and its polarization properties indicated that its origin lay in the synchrotron process. As we will discuss in Chapter 3, in this process radiation comes from electrons accelerated by a magnetic field. Thus a typical radio source has as its energy reservoir the dynamical energy of relativistic particles and magnetic field energy.

In 1958 Geoffrey Burbidge drew attention to the enormous size of this energy reservoir.

The year 1963 marks a watershed in extragalactic astronomy. The optical identification of radio sources 3C 273 and 3C 48 and the measurement of their redshifts demonstrated to astronomers the existence of a new class of energy sources that have a star-like appearance, yet produce luminous energy at a rate comparable to a galaxy of a hundred billion (1011) stars.

The quasi-stellar objects (QSOs) or ‘quasars’ as these sources came to be called, arrived on astrophysicists' plates just about when they had digested the long-standing mystery of stellar energy. By the 1960s, the problems of stellar structure and evolution built on the pillars erected by Eddington, Milne, Chandrasekhar, Bethe, Lyttleton, Schwarzschild and Hoyle had been tackled successfully, thanks to the advent of fast electronic computers. The quasars, however, presented challenges of an altogether different nature. How could so much energy come with such rapid variability out of such a compact region and be distributed over such a wide range of wavelengths?

The classic book Quasi-Stellar Objects by Geoffrey and Margaret Burbidge, published in 1967, captured this early excitement and posed the numerous challenges of quasar astronomy very succinctly. Now, three decades later, we have the benefits of vast progress in the techniques of observational extragalactic astronomy and the intricate sophistication of ideas in high energy astrophysics. Yet it is fair to say that the understanding of quasars and the related field of active galactic nuclei (AGN) has not reached the same level of success that stellar studies had attained thirty years ago.

Introduction

The early ideas of Hoyle and Fowler (1963) concerning gravitational collapse to a compact object that would serve as an energy reservoir for a quasar found a modified expression in the black hole accretion disk paradigm, a few years later. This paradigm had been invoked and worked well in the understanding of binary X-ray sources in the Galaxy. In the binary star context the compact member is taken to be either a neutron star or a black hole with mass of stellar order. For quasars and AGN, the compact masses would have to be several orders of magnitude higher, as already pointed out by Hoyle and Fowler (1963). The scenario here had therefore to explain how such objects form in the first place, how they generate an accretion disk and jets, and how and with what efficiency is the gravitational energy converted to the observed radiant energy.

In this brief review of the current thinking on the subject we shall follow the excellent account given by Rees (1984) whose basic tenets have remained more or less the same since then.

The formation of a massive black hole

As first pointed out by Hoyle and Fowler (1963), the energy source of a quasar or AGN is gravitational and could arise from a highly collapsed object or a massive black hole. This much is broadly agreed by most workers in the field. The question is, in the first place how does a collapsed massive object come about?

Introduction

The continuum radiation from AGN stretches over the entire range of the electromagnetic spectrum, from the radio to the high energy γ-ray region, where pair production by photons becomes important. The continuum spectrum has an overall complex shape, but it can often be approximated by a simple power law form over fairly wide wavelength intervals. The radiation is produced in elementary processes like synchrotron emission and bremsstrahlung, and is modified by scattering, absorption and reemission. In this chapter and the next we shall consider some aspects of radiation processes which are important to the basic understanding of the continuum spectrum. The discussion will be brief, and the emphasis will be on developing concepts, summarizing important results and providing them in such a form that they can be directly applied to situations pertinent to quasars and AGN. The subject has been treated in detail in a pedagogic manner by Jackson [J75] and Rybicki and Lightman [RL79]. The more advanced and formal aspects have been covered by Blumenthal and Gould (1970) and an excellent summary, especially of the synchrotron process, with application to AGN, may be found in Moffett (1968). Our treatment and notation owe much to these sources.

In the present chapter we will consider mainly synchrotron radiation and some consequences of relativistic radiation. The other processes important to AGN and quasars will be discussed in Chapter 4.