Star Patterns Asterisms and Constellations

2.1.1. Stellar Pattern Recognition

About 15,000 stars are detectable by the human eye, most of them near the limit of visibility. At any one time, we may be able to see a few thousand stars in a dark sky, but we tend to remember only striking patterns of them—asterisms such as the Big Dipper or whole constellations such as Ursa Major (the Big Bear) or Orion (the name of a mythological hunter)—and so it has been for millennia. Today, the entire sky has been divided into constellations; they are not defined according to appearance alone but according to location, and there are no boundary disputes. The modern names and locations are more or less those of Argelander (1799-1875) for the Northern Hemisphere and John Herschel (1824-1896) for the Southern, but the present divisions of the constellations1 were adopted by the International Astronomical Union (IAU), the chief authority on such matters as astronomical nomenclature, in 1930. The IAU has established 88 constellations in the sky; many reflecting an ancient heritage.

The names of the constellations recognized in antiquity were based on

• Mythological figures

• Animals or inanimate objects as perceived in the sky

• Geographical or political analogues

• Associations with seasonal phenomena, or some other basis

As we will show in later chapters, non-Western traditions have perceived a rich variety of star patterns; some include the absence of stars, the "dark constellations."2 Chinese constellations were different from and far more numerous than were those of the Mediterranean area. As far as we are aware, the oldest extant Chinese star chart on paper is contained in a 10th-century manuscript from Dunhuang, but there is far older evidence for sky charting from this area of the world (see §10 and §2.2.3); a compilation by Chhien Lu-Chih listed 284 constellations containing a total of 1464 stars and is said to be based on a Han catalogue (see §10.1.2.3; and Yi, Kistemaker, and Yang (1986) for new maps and a review of historical Chinese star catalogues).

Western constellations in current use largely derive from ancient Mediterranean sources, mainly the Near East and Greece, as we show in §7. The earliest surviving detailed description of the Greek constellations is in the poem Phaenomena by the Greek poet Aratos (Aratus in the Roman sources), ~250 b.c. (Whitfield 1995, p. 23). The constellations portrayed in the poem derive from a work also called Phaenomena, which has not survived, by the Greek astronomer Eudoxos (or Eudoxus) (4th century b.c.). One of the later sources that discusses this work is that of the sole remaining manuscript of Hipparchos (~150 b.c.), one of the greatest astronomers of antiquity. Many of the constellations can be seen as raised images on the Farnese Globe, the oldest extant celestial globe, dated to the 2nd century b.c., but representing a copy of an older work. Aratos mentioned 47 constellations, whereas Claudius Ptolemy (~150 a.d.), the source of much of our knowledge about Hipparchos, referred to 48 in the major astronomical work that we know today as the Almagest.

In ancient Greek usage, the constellations were the figures. For example, in the constellation of Cassiopeia, the star Z Cassiopeiae (abbreviated Z Cas) is described as "the star on the head"; a Cas, as "the star in the breast"; and

1 Boundaries are along coordinates of right ascension and declination referred to the equinox of 1875.0. See sections below for explanations -

of these terms. 2 See §14.2.5, for a Peruvian example.

h Cas as "the star over the throne, just over the thighs." In Perseus, the variable star Algol (ß Per) is described as the "bright one" in the "Gorgon's head." Not all naked eye stars fitted neatly into these groupings, so many stars were omitted from the constellations. Those outside the accepted figures were referred to as "unformed" (a|iöpfwTOt; our word "amorphous" derives from a related word), or "scattered" (orcopàSeç, related to the Greek word for seed, orcopd, broadcast during sowing, and our cognate word, "sporadic"). The IAU reorganization created constellation "homes" for these "unformed" stars.

2.1.2. Star Charts

The depictions of the Greco-Roman constellations as they were known in Ptolemy's time (~150 a.d.) were preserved in Arabic sources, one of the best known being that of the astronomer al-Sufl (10th century). R.H. Allen (1963) states that the sky representations of post-Renaissance Europe derive from those of Albrecht Dürer (1471-1528) of 1515 (Figure 1.1), in which the star positions from Ptolemy's catalogue were set down by another resident of Nürnberg (Nuremberg), a mathematician named Heinvogel. The positions were subsequently improved and more stars added, but the figures of Dürer essentially remained the same through the charts of Bayer (1603), Flamsteed (1729), and Argelander (1843). More details about star charts from 1500 to 1800 can be found in Warner (1979), and an even wider range of charts is found in Stott (1991/1995) and Whitfield (1995).

The representations of the more obvious asterisms differed widely from culture to culture. A familiar example is the Big Dipper, still known in England as the plough, and in Germany and Scandinavia as the Wagen (wagon). In the Roman republic, it was the plow oxen. On many pre-19th-century maps and star charts, the term Septentrion or some variety of this term appears. The expression became synonymous with the North, or northern regions, but originally meant the seven plow oxen. R.H. Allen (1963) says that the Big Dipper was known as a coffin in parts of the Mideast, a wagon or bear in Greece, and a bull's thigh in pre-Hellenistic Egypt. Systematic attempts were made to rename the constellations at various times. Giordano Bruno (1548-1600) sought to invest the sky with figures representing Moral Virtues. Julius Schiller of Augsburg produced the most widely known type of Bible-inspired charts in 1627. R.H. Allen's (1963) encyclopedic search into the origins of star names and constellations reveals several other European attempts to recast the constellations, although the various sources used by him are not always treated critically.

2.1.3. Modern Nomenclature

Today, constellations refer to specified areas on the celestial sphere, whereas an asterism is any apparent grouping of stars. Indeed, one could be forgiven for describing the ancient "constellations" as asterisms. With some exceptions, in modern usage, an asterism is usually smaller than a constellation; for example, the Little Dipper asterism is in the constellation of Ursa Minor, the Little Bear, and the Pleiades is a well-known asterism in the constellation Taurus, the Bull. An exception is the Summer Triangle, composed of the bright stars Vega, Deneb, and Altair in the constellations Lyra, Cygnus, and Aquila, respectively. Even a single star may constitute an asterism. The star Spica, for example, the brightest star in the constellation of Virgo, has been envisaged as a spike of wheat.

Modern common names of naked eye stars, derive from European and Arabic usage, as well as proper names devised by Johann Bayer in 1603. The Bayer designations use lower-case Greek letters and, after these are exhausted, small Roman letters, to identify stars in a given constellation, for example, u Herculis or i Bootis. When these were exhausted, capital Roman letters were used. The lettered type of designation was later extended to the Southern Hemisphere by Nicolas Louis de Lacaille (1763) and John Herschel (1847). The Greek letters are universally accepted, but an alternative designation to the Bayer letters for the fainter stars is that of the Flamsteed numbers (Flamsteed 1725, Vol. 3), as, for example, 44 Bootis = i Bootis. Giuseppe Piazzi (1803) also published star catalogues in 1803 and 1814 (see Piazzi/Foderà Serio 1990). The Flamsteed numbers increase with right ascension, a coordinate that increases from west to east (see §2.2.3). Many catalogues of stars and other objects use positional or sequence numbers, usually increasing with right ascension. The best known star catalog of this kind is the Bright Star Catalog (Hoffleit 1982), which uses the positional sequence numbers of the Harvard Revised Photometry Catalog (Pickering 1908); thus, BS 7001 = HR 7001 = a Lyrae.

Usually, the Greek letter designates the relative brightness of the star within the constellation, but occasionally they were assigned to a positional sequence, as in Ursa Major. In the list of modern constellations, Table 2.1, the star names are in Latin, with the historically earliest names referring to Latin forms of Greek originals. The columns contain both nominative and possessive3 cases of the names, English equivalents, notable stars and other objects, and both modern and ancient asterisms that are within the modern boundaries. Only objects that can be seen unaided under clear and dark sky circumstances are included.

"Double stars" are stars that appear close to each other in the sky; sometimes they are indeed physically close to each other and interact gravitationally, but not always. The pair of stars Mizar and Alcor (Z Ursae Majoris and 80 Ursae Majoris, respectively), in the handle of the Big Dipper, is an example of a naked-eye double.

Types of "variable stars" are named after their prototypes, such as delta Cephei or RR Lyrae. In the Bayer designations, no visible star had been assigned a letter later in the alphabet than Q; consequently, Argelander suggested that designations of R and later would be used solely for variable stars. This scheme has been followed dogmatically to a logical conclusion ever since. When designations to Z became

3 The possessive or genitive case is used in formal star names, e.g., a Canis Majoris, ß Scorpii, ß Lyrae, or S Doradus, literally, the stars labeled a of the constellation Canis Major, ß of Scorpius, and so on.

2.1. Star Patterns: Asterisms and Constellations Table 2.1. Modern constellations.

Name

Meaning

Possessive8

Asterisms/features

Andromeda

Mythological figure (chained lady)

Andromedae

Spiral galaxy M31.

Antlia

Air pump

Antliae

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