Zeus

Zeus (IPA: /zjuːs/; in Greek: nominative: Ζεύς Zeús /zdeús/, genitive: Διός Diós; Modern Greek /'zefs/) in Greek mythology is the king of the gods, the ruler of Mount Olympus and the god of the sky and thunder. His symbols are the thunderbolt, eagle, bull, and oak. In addition to his Indo-European inheritance, the classical "cloud-gatherer" also derives certain iconographic traits from the cultures of the ancient Near East, such as the scepter. Zeus is frequently depicted by Greek artists in one of two poses: standing, striding forward, with a thunderbolt leveled in his raised right hand, or seated in majesty.

Zeus was the child of Cronus and Rhea, and the youngest of his siblings. In most traditions he was married to Hera, although, at the oracle of Dodona, his consort was Dione: according to the Iliad, he is the father of Aphrodite by Dione. He is known for his erotic escapades. These resulted in many godly and heroic offspring, including Athena, Apollo and Artemis, Hermes, Persephone (by Demeter), Dionysus, Perseus, Heracles, Helen, Minos, and the Muses (by Mnemosyne); by Hera, he is usually said to have fathered Ares, Hebe and Hephaestus.

His Roman counterpart was Jupiter and his Etruscan counterpart Tinia. In Hindu mythology his counterpart was Indra with ever common weapon as thunderbolt.

Panhellenic cults of Zeus

The major center where all Greeks converged to pay honor to their chief god was Olympia. Their quadrennial festival featured the famous Games. There was also an altar to Zeus made not of stone, but of ash, from the accumulated remains of many centuries' worth of animals sacrificed there.

Outside of the major inter-polis sanctuaries, there were no modes of worshipping Zeus precisely shared across the Greek world. Most of the titles listed below, for instance, could be found at any number of Greek temples from Asia Minor to Sicily. Certain modes of ritual were held in common as well: sacrificing a white animal over a raised altar, for instance.

Colossal seated Marnas from Gaza portrayed in the style of Zeus. Marnas^[1] was the chief divinity of Gaza. Roman period Istanbul Archaeology Museum)

Bust of Zeus in the British Museum

History

Zeus, poetically referred to by the vocative Zeu pater ("O, father Zeus"), is a continuation of *Di̯ēus, the Proto-Indo-European god of the daytime sky, also called *Dyeus ph₂tēr ("Sky Father").^[2] The god is known under this name in Sanskrit (cf. Dyaus/Dyaus Pita), Latin (cf. Jupiter, from Iuppiter, deriving from the PIE vocative *dyeu-ph₂tēr^[3]), deriving from the basic form *dyeu- ("to shine", and in its many derivatives, "sky, heaven, god").^[2] And in Germanic and Norse mythology (cf. *Tīwaz > OHG Ziu, ON Týr), together with Latin deus, dīvus and Dis(a variation of dīves^[4]), from the related noun *deiwos.^[4] To the Greeks and Romans, the god of the sky was also the supreme god, whereas this function was filled out by Odin among the Germanic tribes. Accordingly, they did not identify Zeus/Jupiter with either Tyr or Odin, but with Thor (Þórr). Zeus is the only deity in the Olympic pantheon whose name has such a transparent Indo-European etymology.^[5]

Role and epithets

Zeus played a dominant role, presiding over the Greek Olympian pantheon. He fathered many of the heroes and was featured in many of their local cults. Though the Homeric "cloud collector" was the god of the sky and thunder like his Near-Eastern counterparts, he was also the supreme cultural artifact; in some senses, he was the embodiment of Greek religious beliefs and the archetypal Greek deity.

Aside from local epithets that simply designated the deity to doing something random at some particular place, the epithets or titles applied to Zeus emphasized different aspects of his wide-ranging authority:

• Zeus Olympios emphasized Zeus's kingship over both the gods in addition to his specific presence at the Panhellenic festival at Olympia.
• A related title was Zeus Panhellenios ('Zeus of all the Hellenes'), to whom Aeacus' famous temple on Aegina was dedicated.
• As Zeus Xenios, Zeus was the patron of hospitality and guests, ready to avenge any wrong done to a stranger.
• As Zeus Horkios, he was the keeper of oaths. Exposed liars were made to dedicate a statue to Zeus, often at the sanctuary of Olympia.
• As Zeus Agoraeus, Zeus watched over business at the agora and punished dishonest traders.
• As Zeus Aegiduchos or Aegiochos he was the bearer of the Aegis with which he strikes terror into the impious and his enemies.^[6][7][8] Others derive this epithet from αίξ ("goat") and οχή and take it as an allusion to the legend of Zeus' suckling at the breast of Amalthea.^[9][10]
• As Zeus Meilichios, "Easy-to-be-entreated", he subsumed an archaic chthonic daimon propitiated in Athens, Meilichios.
• As Zeus Tallaios, or "Solar Zeus", he was worshiped in Crete.

Some local Zeus-cults

In addition to the Panhellenic titles and conceptions listed above, local cults maintained their own idiosyncratic ideas about the king of gods and men. With the epithet Zeus Aetnaeus he was worshiped on Mount Aetna, where there was a statue of him, and a local festival called the Aetnaea in his honor.^[11] Other examples are listed below.

• As Zeus Aeneius or Aenesius, he was worshiped in the island of Cephalenia, where he had a temple on Mount Aenos.^[12]
• As Zeus Agamemnon he was worshipped at Sparta.

Cretan Zeus

With one exception, Greeks were unanimous in recognizing the birthplace of Zeus as Crete. Minoan culture contributed many essentials of ancient Greek religion: "by a hundred channels the old civilization emptied itself into the new", Will Durant observed,^[13] and Cretan Zeus retained his youthful Minoan features. The local child of the Great Mother, "a small and inferior deity who took the roles of son and consort",^[14] whose Minoan name the Greeks Hellenized as Velchanos, was in time asssumed as an epithet by Zeus, as transpired at many other sites, and he came to be venerated in Crete as Zeus Velchanos, the "boy-Zeus", often simply the Kouros.

In Crete, Zeus was worshipped at a number of caves at Knossos, Ida and Palaikastro. In the Hellenistic period a small sanctuary dedicated to Zeus Velchanos was founded at the Aghia Triada site of a long-ruined Minoan palace. Broadly contemporary coins from Phaistos show the form under which he was worshiped: a youth sits among the branches of a tree, with a cockerel on his knees.^[15] On other Cretan coins Velchanos is represented as an eagle and in association with a goddess celebrating a mystic marriage.^[16] Inscriptions at Gortyn and Lyttos record a Velchania festival, showing that Velchanios was still widely venerated in Hellenistic Crete.^[17]

The stories of Minos and Epimenides suggest that these caves were once used for incubatory divination by kings and priests. The dramatic setting of Plato's Laws is along the pilgrimage-route to one such site, emphasizing archaic Cretan knowledge. On Crete, Zeus was represented in art as a long-haired youth rather than a mature adult, and hymned as ho megas kouros "the great youth". Ivory statuettes of the "Divine Boy" were unearthed near the Labyrinth at Knossos]] by Sir Arthur Evans.^[18] With the Kouretes, a band of ecstatic armed dancers, he presided over the rigorous military-athletic training and secret rites of the Cretan paideia.

The myth of the death of Cretan Zeus, localised in numerous mountain sites though only mentioned in a comparatively late source, Callimachus,^[19] together with the assertion of Antoninus Liberalis that a fire shone forth annually from the birth-cave the infant shared with a mythic swarm of bees, suggests that Velchanos had been an annual vegetative spirit.^[20] The Hellenistic writer Euhemerus apparently proposed a theory that Zeus had actually been a great king of Crete and that posthumously his glory had slowly turned him into a deity. The works of Euhemerus himself have not survived, but Christian patristic writers took up the suggestion with enthusiasm.

Zeus Lykaios in Arcadia

For more details on this topic, see Lykaia.

The epithet Lykaios ("wolf-Zeus") is assumed by Zeus only in connection with the archaic festival of the Lykaia on the slopes of Mount Lykaion ("Wolf Mountain"), the tallest peak in rustic Arcadia; Zeus had only a formal connection^[21] with the rituals and myths of this primitive rite of passage with an ancient threat of cannibalism and the possibility of a werewolf transformation for the ephebes who were the participants.^[22] Near the ancient ash-heap where the sacrifices took place^[23] was a forbidden precinct in which, allegedly, no shadows were ever cast.^[24] According to Plato (Republic 565d-e), a particular clan would gather on the mountain to make a sacrifice every nine years to Zeus Lykaios, and a single morsel of human entrails would be intermingled with the animal's. Whoever ate the human flesh was said to turn into a wolf, and could only regain human form if he did not eat again of human flesh until the next nine-year cycle had ended. There were games associated with the Lykaia, removed in the fourth century to the first urbanization of Arcadia, Megalopolis; there the major temple was dedicated to Zeus Lykaios.

Apollo, too had an archaic wolf-form, Apollo Lycaeus, worshipped in Athens at the Lykeion, or Lyceum, which was made memorable as the site where Aristotle walked and taught.

Subterranean Zeus

Although etymology indicates that Zeus was originally a sky god, many Greek cities honored a local Zeus who lived underground. Athenians and Sicilians honored Zeus Meilichios ("kindly" or "honeyed") while other cities had Zeus Chthonios ("earthy"), Katachthonios ("under-the-earth) and Plousios ("wealth-bringing"). These deities might be represented as snakes or in human form in visual art, or, for emphasis as both together in one image. They also received offerings of black animal victims sacrificed into sunken pits, as did chthonic deities like Persephone and Demeter, and also the heroes at their tombs. Olympian gods, by contrast, usually received white victims sacrificed upon raised altars.

In some cases, cities were not entirely sure whether the daimon to whom they sacrificed was a hero or an underground Zeus. Thus the shrine at Lebadaea in Boeotia might belong to the hero Trophonius or to Zeus Trephonius ("the nurturing"), depending on whether you believe Pausanias, or Strabo. The hero Amphiaraus was honored as Zeus Amphiaraus at Oropus outside of Thebes, and the Spartans even had a shrine to Zeus Agamemnon.

galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and possibly a hypothetical substance known as dark matter.^[1][2] The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million^[3] (10⁷) stars up to giants with one trillion^[4] (10¹²) stars, all orbiting a common center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy,^[5] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving, dusty arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.^[6]

There are probably more than 100 billion (10¹¹) galaxies in the observable universe.^[7] Most galaxies are 1,000 to 100,000^[4] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs).^[8] Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.^[9]

Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus

Etymology

The word galaxy derives from the Greek term for our own galaxy, galaxias (γαλαξίας), or kyklos galaktikos, meaning "milky circle" for its appearance in the sky. In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Hera's breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.^[11]

In the astronomical literature, the capitalized word 'Galaxy' is used to refer to our (Milky Way) galaxy, to distinguish it from the billions of other galaxies.

The term Milky Way first appeared in the English language in a poem by Chaucer.

"See yonder, lo, the Galaxyë
Which men clepeth the Milky Wey,
For hit is whyt."

—Geoffrey Chaucer, Geoffrey Chaucer The House of Fame, c. 1380.^[12]

When William Herschel constructed his catalog of deep sky objects, he used the name spiral nebula for certain objects such as M31. These would later be recognized as immense conglomerations of stars, when the true distance to these objects began to be appreciated, and they would be termed island universes. However, the word universe was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.^[13]

[edit] Observation history

The realization that we live in a galaxy, and that there were, in fact, many other galaxies, parallels discoveries that were made about the Milky Way and other nebulae in the night sky.

[edit] The Milky Way

Galactic Center of Milky Way and a meteor

The Greek philosopher Democritus (450–370 B.C.) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.^[14] Aristotle (384-322 B.C.), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions."^[15] The Arabian astronomer, Alhazen (965-1037 A.D.), refuted this by making the first attempt at observing and measuring the Milky Way's parallax,^[16] and he thus "determined that because the Milky Way had no parallax, it was very remote from the earth and did not belong to the atmosphere."^[17]

The Persian astronomer, Abū Rayhān al-Bīrūnī (973-1048), proposed the Milky Way galaxy to be a collection of countless nebulous stars.^[18] Ibn Bajjah ("Avempace", d. 1138) proposed the Milky Way to be made up of many stars but appears to be a continuous image due to the effect of refraction in the Earth's atmosphere.^[15] Ibn Qayyim Al-Jawziyya (1292-1350) proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars" and that these stars are larger than planets.^[19]

Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars.^[20] In 1750 Thomas Wright, in his An original theory or new hypothesis of the universe, speculated (correctly) that the Galaxy might be a rotating body of a huge number of stars held together by gravitational forces, akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk.^[21] In a treatise in 1755, Immanuel Kant elaborated on Wright's idea about the structure of the Milky Way.

The shape of the Milky Way as deduced from star counts by William Herschel in 1785; the solar system was assumed to be near the center.

The first attempt to describe the shape of the Milky Way and the position of the Sun in it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center.^[22][23] Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.^[21] Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters, the present picture of our galaxy, the Milky Way, emerged.^[24]

[edit] Distinction from other nebulae

Sketch of the Whirlpool Galaxy by Lord Rosse in 1845

In the 10th century, the Persian astronomer, Abd al-Rahman al-Sufi (known in the West as Azophi), made the earliest recorded observation of the Andromeda Galaxy, describing it as a "small cloud".^[25] Al-Sufi also identified the Large Magellanic Cloud, which is visible from Yemen, though not from Isfahan; it was not seen by Europeans until Magellan's voyage in the 16th century.^[26][27] These were the first galaxies other than the Milky Way to be observed from Earth. Al-Sufi published his findings in his Book of Fixed Stars in 964.

In 1054, the creation of the Crab Nebula resulting from the SN 1054 supernova was observed by Chinese and Arab/Persian astronomers. The Crab Nebula itself was observed centuries later by John Bevis in 1731, followed by Charles Messier in 1758 and then by the Earl of Rosse in the 1840s.^[28]

In 1750 Thomas Wright, in his An original theory or new hypothesis of the universe, speculated (correctly) that Milky Way was a flattened disk of stars, and that some of the nebulae visible in the night sky might be separate Milky Ways.^[21][29] In 1755 Immanuel Kant introduced the term "island universe" for these distant nebulae.

Toward the end of the 18th century, Charles Messier compiled a catalog containing the 109 brightest nebulae (celestial objects with a nebulous appearance), later followed by a larger catalog of 5,000 nebulae assembled by William Herschel.^[21] In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.^[30]

In 1917, Heber Curtis had observed the nova S Andromedae within the "Great Andromeda Nebula" (Messier object M31). Searching the photographic record, he found 11 more novae. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our galaxy. As a result he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies.^[31]

Photograph of the "Great Andromeda Nebula" from 1899, later identified as the Andromeda Galaxy

In 1920 the so-called Great Debate took place between Harlow Shapley and Heber Curtis, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that the Great Andromeda Nebula was an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.^[32]

The matter was conclusively settled by Edwin Hubble in the early 1920s using a new telescope. He was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.^[33] In 1936 Hubble produced a classification system for galaxies that is used to this day, the Hubble sequence.^[34]

[edit] Modern research

In 1944 Hendrik van de Hulst predicted microwave radiation at a wavelength of 21 cm resulting from interstellar atomic hydrogen gas;^[35] this radiation was observed in 1951. The radiation allowed for much improved study of the Milky Way Galaxy, since it is not affected by dust absorption and its Doppler shift can be used to map the motion of the gas in the Galaxy. These observations led to the postulation of a rotating bar structure in the center of the Galaxy.^[36] With improved radio telescopes, hydrogen gas could also be traced in other galaxies.

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). The distance is from the galactic core.

In the 1970s it was discovered in Vera Rubin's study of the rotation speed of gas in galaxies that the total visible mass (from the stars and gas) does not properly account for the speed of the rotating gas. This galaxy rotation problem is thought to be explained by the presence of large quantities of unseen dark matter.^[37]

Beginning in the 1990s, the Hubble Space Telescope yielded improved observations. Among other things, it established that the missing dark matter in our galaxy cannot solely consist of inherently faint and small stars.^[38] The Hubble Deep Field, an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion galaxies in the universe.^[39] Improved technology in detecting the spectra invisible to humans (radio telescopes, infrared cameras, and x-ray telescopes) allow detection of other galaxies that are not detected by Hubble. Particularly, galaxy surveys in the zone of avoidance (the region of the sky blocked by the Milky Way) have revealed a number of new galaxies.^[40]

[edit] Types and morphology

Main article: Galaxy morphological classification

Types of galaxies according to the Hubble classification scheme. An E indicates a type of elliptical galaxy; an S is a spiral; and SB is a barred-spiral galaxy.^{[note 1]}

Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as star formation rate (in starburst galaxies) and activity in the core (in active galaxies).^[6]

[edit] Ellipticals

Main article: Elliptical galaxy

The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. Consequently these galaxies also have a low portion of open clusters and a reduced rate of new star formation. Instead the galaxy is dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions. In this sense they have some similarity to the much smaller globular clusters.^[41]

The largest galaxies are giant ellipticals. Many elliptical galaxies are believed to form due to the interaction of galaxies, resulting in a collision and merger. They can grow to enormous sizes (compared to spiral galaxies, for example), and giant elliptical galaxies are often found near the core of large galaxy clusters.^[42] Starburst galaxies are the result of such a galactic collision that can result in the formation of an elliptical galaxy.