The Antigonids took longer to secure their position than their rivals the Ptolemies and Seleucids. For the Successors possession of the Macedonian kingdom was an irresistible temptation, and competition was intense, especially after the death of Cassander. Further instability in Macedon was caused by the Celtic invasion, but it also gave Antigonus Gonatas the opportunity to establish himself and his dynasty in the country. But Macedonian power remained contested and was never again as dominant as under Philip II and Alexander. Besides constant pressure from the northern hinterland, and the hostility of the Ptolemies who sought to counteract any resurgence of Antigonid power in the Aegean, the Greek world to the south presented problems of a kind that the monarchies in Asia, ruling over predominantly non-Greek populations, did not face. Though unable to challenge successfully Macedonian overlordship Athens could not be reconciled to it. Sparta under the leadership of ambitious kings obstinately tried to restore her power in the Peloponnese. though with disastrous results in the end. In regions of the Greek world that had not hitherto played a major role new political organisations emerged: the Aetolian League in north-west Greece and the Achaean League in the northern Peloponnese, which for a while successfully challenged Macedonian power, before being curtailed by Antigonus Doson. On the eve of Roman intervention the Greek mainland remained as disunited as before.

While sharing features common to all the monarchies of the age, the Ptolemaic dynasty was peculiar in several respects because of its location in Egypt and its position in the world of the time. The monarchy was doublefaced and thus ambiguous in character; the rulers were successors to the Pharaohs in Egypt, but at the same time Greek-style kings in a wider international context. The availability of a wealth of evidence from Egypt, especially papyri, which supplements Greek literary and epigraphic sources, means also that Ptolemaic history is more fully documented than that of its rivals.

Based in an ancient land with a strong identity, the Ptolemies could not avoid adapting to Egyptian traditions of monarchy and conciliating the powerful native priesthood. The occasional incidence of brother– sister marriage in the dynasty may have reflected Egyptian influence. The foundation of Ptolemaic prosperity was the agricultural wealth of the sheltered Nile valley and the labour of the large Egyptian population.

Yet in parallel with this the Ptolemies were seen as members of the international ‘royal club’, active in the wider Greek world, anxious to patronise Greek culture and promote themselves to Greek audiences, and involved in a protracted rivalry with the Antigonids in Macedon and the Seleucids in Asia (for the so-called ‘Syrian Wars’ cf. successively 163, 183, 266, 275, 193, 211). ‘The kings of Egypt liked to be called Macedonians, as in fact they were,’ notes Pausanias (X.7.8, cf. VI.3.1). The dynasty closely identified with Alexander, and intermarried not with Egyptians but with dynasties outside Egypt.

The Attalids differed in several ways from the Antigonids, Seleucids and Ptolemies. Like the rulers of Bithynia, Pontus and other monarchies (chapter 3, Introduction), they were not part of the Macedonian ‘royal club’ of the first generation after Alexander (chapter 2), but started under Philetaerus as local rulers in Pergamum with initially limited territory, and only achieved their royal status under Attalus I, the third ruler in the dynasty. The dynasty prided itself on its cohesiveness and freedom from internal challenges, in contrast to the Seleucids and Ptolemies. Unlike the Seleucids and Ptolemies, the Attalid rulers avoided deification of themselves in their lifetime. They sided with Rome in her intervention against Philip V then Antiochus III and as a result achieved their greatest power and prosperity when those monarchies had been curtailed by defeat at Roman hands. It was therefore appropriate that Rome should eventually inherit the kingdom she had helped to build up. Pergamum, the Attalids' capital city, maintained civic forms but was closely controlled by the rulers and lavishly beautified by them. From the beginning the Attalids cultivated their reputation in the Greek world, locally in Asia Minor, and further afield in the Aegean and on the mainland. Adapting the pose of classical Athens against the ‘barbarians of Asia’, they presented themselves as champions of the Greek world against the Celtic invaders in Anatolia. The reputation they enjoy in Greek sources is, not surprisingly, predominantly favourable.

Histories and surveys of the Hellenistic world commonly begin with the death of Alexander in 323. This may be justified if the subject is to be kept within manageable limits, yet the invasion of the Persian empire is arguably the natural starting point.

Alexander is by himself a large subject, and this chapter can only highlight major episodes and themes in his career, with emphasis on those of particular relevance for Alexander's ‘Successors’ and the world after him. The conquest of the Persian empire, the most profitable war of its kind in antiquity, was the precondition for the expansion of the Greek world and the influx of Greek settlers into western Asia. The result was not the literal ‘hellenisation’ of Asia, despite some optimistic generalisations, but it changed the face of the east, though Greeks remained numerically a minority amidst the indigenous populations. The movement of colonists during Alexander's time was apparently on a modest scale, and there is evidence of reluctance on their part to settle far away from the Aegean world. But the process gathered momentum after Alexander's death, as the consequences of the disappearance of the Persian empire became clear and the new rulers were anxious to attract Greek settlers to their emerging kingdoms. Alexander's own city foundations were seemingly few in number and not initially very successful, but they were important in starting a movement which his Successors pursued on a larger scale after his death.

This is the second and enlarged edition of a book first published in 1981 under the title The Hellenistic world from Alexander to the Roman conquest. A selection of ancient sources in translation. Since its original publication there has been a veritable explosion of scholarly work on this period, and the Hellenistic age has moved from a relatively marginal position in academic curricula to one where it is entitled to receive the same kind of attention as any other period in antiquity. I am very grateful to Cambridge University Press for giving me the opportunity to revisit the work after more than twenty years and take into account the development of scholarship that has taken place in the intervening period.

The new edition is similar in scope, purpose and design to the first one, and all the texts previously included have been retained. Nearly 50 texts have been added, some newly discovered or recently published, others already known but not included in the first edition. The book has been completely revised and updated. The structure and presentation of the original has been preserved, though for the sake of clarity chapter 5 (The Seleucids and Asia) is now organised in a single chronological section and chapter 7 (The Ptolemies and Egypt) has been divided into two not three sections, both organised chronologically. Each chapter has been provided with a short introduction to give a conspectus of the texts included.

The importance of the Sun as the most observable of all stars cannot be overstated. As shown in Figure 15.1, no other star can be studied with the degree of detail that we achieve in even the simplest observations of this source of all of our light and energy. As a result, what we have learned from the Sun we have applied in our study and analysis of the stars. Our knowledge of the sizes and distances of the stars is based upon our knowledge of the Sun. Also, we calibrate the luminosities of the stars in terms of our measurements of the output of energy from the Sun. In this chapter we shall first describe methods of observing the Sun in simple ways that can be used by anyone with a telescope. Then, we shall move on to more specialized methods and instruments that are used at observatories dedicated mainly to solar research.

Observing the Sun with a small telescope

The Sun is so bright that one should never try to make direct, naked-eye or telescopic observations of it. This is an absolute rule, for the observer can be blinded by even a brief attempt. There are, however, safe ways to view the Sun, and some of these require no complex equipment.

The most readily available method of seeing the Sun's apparent surface or photosphere is by means of eyepiece projection.

The general term “astrometry” is used to describe methods by which the positions of stars may be determined. We noted briefly in Chapter 1 that meridian telescopes were used to determine the right ascensions and declinations of stars, and we wish to repeat here that this work has been of fundamental importance to all astronomers. However, meridian telescopes have now been made obsolete by space-based observations and ground-based telescopes equipped with CCDs. Meridian telescopes were never an effective way to determine the coordinates of faint stars, galaxies, comets, and asteroids.

Today, most astrometric measurements are made with area detectors. The positions of stars on an image formed by a telescope are directly related to their actual positions in the sky, so it might seem that the analysis should be simple and straightforward. This is not really the case. The geometry in Figure 11.1 shows the basic relationships. The center of the lens of a telescope is at C and the focal plane is at FF′. A well-made lens should produce an image of plane GG′ in the plane FF′. The plane GG′ may be thought of as being tangent to the celestial sphere at point A. The sky appears as a spherical dome on which the stars appear as points. Thus, in a photograph a star at S is projected to T on the tangent plane, and an image of T is formed at T′.

Observational astronomers have taken advantage of each new development in detector technology. We compared visual observations, photographic plates, photoelectric photometers, and CCD cameras in Chapter 8. Our purpose in this chapter is to discuss how astronomers employ modern optical light detectors to measure astronomical sources in a scientifically useful way. We will focus our discussions on photoelectric and especially CCD photometry.

Fundamentally, there are two approaches to astronomical photometry. The simplest, differential photometry, compares sources sufficiently close together on the sky so that differential first-order extinction can be neglected. More complex is all-sky photometry, which takes full account of the extinction terms for stars observed far apart on the sky over the course of a night. In addition, photometry is done differently with photoelectric photometers compared to CCD cameras. We will begin with a short overview of photoelectric photometry and spend most of the chapter on CCD photometry.

Photoeletric photometry

As we noted in Chapter 8, a photoelectric photometer is of a fundamentally different design than a CCD camera. A single-channel photometer can be trained on only one star at a time. It is important that the star be carefully centered in its aperture. Often a range of aperture sizes is available; the smaller apertures are used in crowded fields and also when the seeing is very good. In between measurements of a star it is necessary to take measurements of the sky.

Many astronomy instructors adopted the first edition of Observational Astronomy as their primary text in advanced undergraduate courses. One of us (GG) used it as the primary text for an advanced undergraduate course in astronomy beginning in 1997. Unfortunately, the first edition went out of print in the late 1990s. By that time it had also become apparent that it was in need of revision. In particular, the charge coupled device (CCD) had already displaced nearly all other detectors in astronomy, but the first edition included only a short appendix on CCDs. Several chapters, instead, focused on photographic techniques. These included photometry, astrometry and spectroscopy. We have replaced all discussions of photographic techniques with CCD techniques in the present edition. We eliminated the chapters on classification of stellar spectra and radio astronomy and added chapters on light and detectors. In addition, we have reordered the material in several chapters in a way we hope is more pedagogically useful.

Most of the discussions about classical astronomical instruments, such as plate measuring engines and filar micrometers, have also been reduced or eliminated. The first edition remains a useful resource on these topics, and we encourage the interested reader to check with their local university library for copies.

The present edition of Observational Astronomy was the Master's thesis project of David Oesper at Iowa State University.

The intersection of three great circles on the surface of a sphere forms a three-sided figure. Such a figure is referred to as a spherical triangle, and it has some interesting properties. For example, the sum of the angles in a spherical triangle will usually be greater than 180°, whereas in a plane triangle this sum is exactly 180°. Consider the spherical triangle formed by the celestial equator and the hour circles of the vernal equinox and a star as in Figure 4.1. (An hour circle is a great circle that passes through a specified point on the celestial sphere as well as the north and south celestial poles.) The intersections of the three great circles have been labeled A, B, and C. Circles through the poles cross the equator at angles of 90°, so ∠B and ∠C are each equal to 90°, and the sum of the three angles will necessarily be greater than 180°.

The intersection of two planes cutting through a sphere forms an angle in a spherical triangle on the surface of the sphere. Each plane must pass through the center of the sphere. Thus, ∠A in Figure 4.1 is the angle between the hour circle planes through the vernal equinox and through the star. Note that ∠A is also equal to ∠BOC.

It is customary, just as in plane trigonometry, to label the sides of a triangle with lower case letters a, b, and c indicating the sides opposite the angles A, B, and C. Note that the length of a side is expressed in terms of an angle measured from the center of the sphere, as shown in Figure 4.2.