Uranometria is the short title of a star atlas produced by Johann Bayer. It was published in Augsburg in 1603 by Christoph Mang under the full title Uranometria: omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa; this translates to "Uranometria, containing charts of all the constellations, drawn by a new method and engraved on copper plates". The word "Uranometria" derives from Urania, Muse of the heavens and "uranos" the Greek word for sky / heavens. A literal translation of "Uranometria" is "Measuring the Heavens", it was the first atlas to cover the entire celestial sphere. Uranometria contained 51 star charts, engraved on copper plates by Alexander Mair; the first 48 charts illustrate each of the 48 Ptolemaic constellations. The 49th chart introduces 12 new constellations in the deep southern sky which were unknown to Ptolemy; the final two charts are planispheres labeled "Synopsis coeli superioris borea" and "Synopsis coeli inferioris austrina," or, "Overview of the northern hemisphere" and "Overview of the southern hemisphere."
Each plate includes a grid for determining the position of each star to fractions of a degree. The positions used by Bayer to create the Uranometria were taken from the expanded 1,005 star catalog of Tycho Brahe. Brahe's expanded list had circulated in manuscript since 1598 and was available in graphic form on the celestial globes of Petrus Plancius and Willem Blaeu, it was first published in tabular form in Johannes Kepler's Rudolphine Tables of 1627. The use of Brahe's catalog allowed for better accuracy than Ptolemy's somewhat limited star listing; the stars listed in Uranometria total over 1,200, indicating that Brahe's catalog was not the only source of information used. Bayer took the southern star positions and constellation names for the 49th plate from the catalog of Dutch navigator Pieter Dirkszoon Keyser, who corrected the older observations of Amerigo Vespucci and Andrea Corsali, as well as the report of Pedro de Medina. Uranometria contains many more stars than did any previous star atlas, though the exact number is disputed as not all stars on the charts are labeled.
Each of the constellations' stars are overlain on an engraved image of the subject of the constellation. For reasons unknown, many of the human constellations are engraved as figures seen from behind whereas they had traditionally been rendered as facing the Earth; this oddity led to some confusion in the literal meanings of certain star names. Uranometria introduced the convention of labelling stars by Greek and Latin letters, known as Bayer star designations, a system, still used today. In the first edition of Uranometria a table of stars was printed on the back of each plate; this made it impossible to consult the table while looking at the chart. Worse still, the lettering of the table spoiled the chart. All editions of the Uranometria omitted the tables, which were instead printed in a separate catalogue called Explicatio characterum aeneis Uranometrias; this separate catalogue was marred by numerous typographical errors which became worse with subsequent editions. The engraved title page of Uranometria is signed in the shadows of the central scroll at the bottom with the monogram AMF, for "Alexander Mair fecit", the date MDCIII.
It features an architectural motif with the full title in the center. On pedestals to either side stand figures of Atlas and Hercules. Inscriptions in the pedestals read, "Atlanti uetustiss astronom magistro" and "Herculi uetustiss astronom discipulo". Across the top of the title page are engraved several additional figures. In the upper left is Apollo, personifying the sun. Top center is the Earth goddess Cybele with two lions on leashes. Upper right is Diana, personifying the Moon, with a cape of stars. Beneath the title banner is a figure of Capricorn and beneath that a view of Augsburg. Bayer objects Star catalogue Uranography Uranometria, 1603 - Full digital facsimile, Linda Hall Library U. S. Naval Observatory: Historical Artwork Collection
Carina is a constellation in the southern sky. Its name is Latin for the keel of a ship, it was part of the larger constellation of Argo Navis until that constellation was divided into three pieces, the other two being Puppis, Vela. Carina was once a part of Argo Navis, the great ship of Jason and the Argonauts who searched for the Golden Fleece; the constellation of Argo was introduced in ancient Greece. However, due to the massive size of Argo Navis and the sheer number of stars that required separate designation, Nicolas Louis de Lacaille divided Argo into three sections in 1763, including Carina. In the 19th century, these three became established as separate constellations, were formally included in the list of 88 modern IAU constellations in 1930. Lacaille kept a single set of Greek letters for the whole of Argo, separate sets of Latin letter designations for each of the three sections. Therefore, Carina has the α, β and ε, Vela has γ and δ, Puppis has ζ, so on. Carina contains Canopus, a white-hued supergiant, the second brightest star in the night sky at magnitude −0.72, 313 light-years from Earth.
Alpha Carinae, as Canopus is formally designated, is a variable star that varies by 0.1 magnitudes. Its traditional name comes from the mythological Canopus, a navigator for Menelaus, king of Sparta. There are several other stars above magnitude 3 in Carina. Beta Carinae, traditionally called Miaplacidus, is a blue-white hued star of magnitude 1.7, 111 light-years from Earth. Epsilon Carinae is an orange-hued giant star bright to Miaplacidus at magnitude 1.9. Another bright star is the blue-white hued Theta Carinae. Theta Carinae is the most prominent member of the cluster IC 2602. Iota Carinae is a white-hued supergiant star of 690 light-years from Earth. Eta Carinae is the most prominent variable star in Carina, it was first discovered to be unusual in 1677, when its magnitude rose to 4, attracting the attention of Edmond Halley. Eta Carinae is inside NGC 3372 called the Carina Nebula, it had a long outburst in 1827, when it brightened to magnitude 1, only fading to magnitude 1.5 in 1828. Its most prominent outburst made Eta Carinae the equal of Sirius.
However, since 1843, Eta Carinae has remained placid, having a magnitude between 6.5 and 7.9. However, in 1998, it brightened though only to magnitude 5.0, a far less drastic outburst. Eta Carinae is a binary star, with a companion. There are several less prominent variable stars in Carina. L Carinae is a Cepheid variable noted for its brightness, it is a yellow-hued supergiant star with a minimum magnitude of 4.2 and a maximum magnitude of 3.3. Two bright Mira variable stars are in Carina: S Carinae. R Carinae has a minimum magnitude of 10.0 and a maximum magnitude of 4.0. Its period is 309 days and it is 416 light-years from Earth. S Carinae is similar, with a minimum magnitude of 10.0 and a maximum magnitude of 5.0. However, S Carinae has a shorter period – 150 days, though it is much more distant at 1300 light-years from Earth. Carina is home to binary stars. Upsilon Carinae is a binary star with two blue-white hued giant components, 1600 light-years from Earth; the primary is of magnitude 3.0 and the secondary is of magnitude 6.0.
Two asterisms are prominent in Carina. One is known as the'Diamond Cross', larger than the Southern Cross, from the perspective of the southern hemisphere viewer, upside down, the long axes of the two crosses being close to parallel. Another asterism in the constellation is the False Cross mistaken for the Southern Cross, an asterism in Crux; the False Cross consists of two stars in Carina, Iota Carinae and Epsilon Carinae, two stars in Vela, Kappa Velorum and Delta Velorum. Carina is known for its namesake nebula, NGC 3372, discovered by French astronomer Nicolas Louis de Lacaille in 1751, which contains several nebulae; the Carina Nebula overall is an extended emission nebula 8,000 light-years away and 300 light-years wide that includes vast star-forming regions. It has an apparent diameter of over 2 degrees, its central region is called the Keyhole Nebula. This was described in 1847 by John Herschel, likened to a keyhole by Emma Converse in 1873; the Keyhole is about seven light-years wide and is composed of ionized hydrogen, with two major star-forming regions.
The Homunculus Nebula is a planetary nebula visible to the naked eye, being ejected by the erratic luminous blue variable star Eta Carinae, the most massive visible star known. Eta Carinae is so massive that it has reached the theoretical upper limit for the mass of a star and is therefore unstable, it is known for its outbursts. Because of this instability and history of outbursts, Eta Carinae is considered a prime supernova candidate for the next several hundred thousand years because it has reached the end of its estimated million-year life span. NGC 2516 is an open cluster, both quite large (ap
The South Pole known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of Earth and lies on the opposite side of Earth from the North Pole. Situated on the continent of Antarctica, it is the site of the United States Amundsen–Scott South Pole Station, established in 1956 and has been permanently staffed since that year; the Geographic South Pole is distinct from the South Magnetic Pole, the position of, defined based on Earth's magnetic field. The South Pole is at the center of the Southern Hemisphere. For most purposes, the Geographic South Pole is defined as the southern point of the two points where Earth's axis of rotation intersects its surface. However, Earth's axis of rotation is subject to small "wobbles", so this definition is not adequate for precise work; the geographic coordinates of the South Pole are given as 90°S, since its longitude is geometrically undefined and irrelevant.
When a longitude is desired, it may be given as 0°. At the South Pole, all directions face north. For this reason, directions at the Pole are given relative to "grid north", which points northwards along the prime meridian. Along tight latitude circles, clockwise is east, counterclockwise is west, opposite to the North Pole; the Geographic South Pole is located on the continent of Antarctica. It sits atop a featureless, barren and icy plateau at an altitude of 2,835 metres above sea level, is located about 1,300 km from the nearest open sea at Bay of Whales; the ice is estimated to be about 2,700 metres thick at the Pole, so the land surface under the ice sheet is near sea level. The polar ice sheet is moving at a rate of 10 metres per year in a direction between 37° and 40° west of grid north, down towards the Weddell Sea. Therefore, the position of the station and other artificial features relative to the geographic pole shift over time; the Geographic South Pole is marked by a stake in the ice alongside a small sign.
The sign records the respective dates that Roald Amundsen and Robert F. Scott reached the Pole, followed by a short quotation from each man, gives the elevation as "9,301 FT.". A new marker stake is fabricated each year by staff at the site; the Ceremonial South Pole is an area set aside for photo opportunities at the South Pole Station. It is located some meters from the Geographic South Pole, consists of a metallic sphere on a short bamboo pole, surrounded by the flags of the original Antarctic Treaty signatory states. Amundsen's Tent: The tent was erected by the Norwegian expedition led by Roald Amundsen on its arrival on 14 December 1911, it is buried beneath the snow and ice in the vicinity of the Pole. It has been designated a Historic Site or Monument, following a proposal by Norway to the Antarctic Treaty Consultative Meeting; the precise location of the tent is unknown, but based on calculations of the rate of movement of the ice and the accumulation of snow, it is believed, as of 2010, to lie between 1.8 and 2.5 km from the Pole at a depth of 17 m below the present surface.
Argentine Flagpole: A flagpole erected at the South Geographical Pole in December 1965 by the First Argentine Overland Polar Expedition has been designated a Historic Site or Monument following a proposal by Argentina to the Antarctic Treaty Consultative Meeting. In 1820, several expeditions claimed to have been the first to have sighted Antarctica, with the first being the Russian expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev; the first landing was just over a year when American Captain John Davis, a sealer, set foot on the ice. The basic geography of the Antarctic coastline was not understood until the mid-to-late 19th century. American naval officer Charles Wilkes claimed that Antarctica was a new continent, basing the claim on his exploration in 1839–40, while James Clark Ross, in his expedition of 1839–43, hoped that he might be able to sail all the way to the South Pole. British explorer Robert Falcon Scott on the Discovery Expedition of 1901–04 was the first to attempt to find a route from the Antarctic coastline to the South Pole.
Scott, accompanied by Ernest Shackleton and Edward Wilson, set out with the aim of travelling as far south as possible, on 31 December 1902, reached 82°16′ S. Shackleton returned to Antarctica as leader of the British Antarctic Expedition in a bid to reach the Pole. On 9 January 1909, with three companions, he reached 88°23' S – 112 miles from the Pole – before being forced to turn back; the first men to reach the Geographic South Pole were the Norwegian Roald Amundsen and his party on December 14, 1911. Amundsen named his camp Polheim and the entire plateau surrounding the Pole King Haakon VII Vidde in honour of King Haakon VII of Norway. Robert Falcon Scott returned to Antarctica with his second expedition, the Terra Nova Expedition unaware of Amundsen's secretive expedition. Scott and four other men reached the South Pole on January 17, 1912, thirty-four days after Amundsen. On the return trip and his four companions all died of starvation and extreme cold. In 1914 Ernest Shackleton's Imperial Trans-Antarctic Expedition set out with the goal of crossing Antarctica via the South Pole, but his ship, the Endurance, was frozen in pack ice and sank 1
Argo Navis, or Argo, was a large constellation in the southern sky that has since been divided into the three constellations of Carina and Vela. The genitive was "Argus Navis", abbreviated "Arg". Flamsteed and other early modern astronomers called the constellation just Navis, genitive "Navis", abbreviated "Nav", it was identified in Greek mythology with the Argo, the ship used by Jason and the Argonauts that sailed to Colchis in search of the Golden Fleece. The original constellation is presently found near the southern horizon of the Mediterranean sky, becoming visible in springtime and sailed westward, skimming along the "river of the Milky Way." Due to precession of the equinoxes, many of the stars of Argo have been shifted farther south since Classical times, far fewer of its stars are visible today from the latitudes of the Mediterranean. This includes Canopus or α Carinae. All the stars of Argo Navis are visible south of the equator, pass near zenith from southern temperate latitudes. Argo Navis was long-known to Greek observers, who are believed to have derived it from Egypt around 1000 BC.
For example, Plutarch identified Argo with the Egyptian constellation called the "Boat of Osiris." Although some academics theorized a Sumerian origin related to the Epic of Gilgamesh, this hypothesis has been rejected as there is no evidence that the Sumerians or other Mesopotamian culture considered these stars, or any portion of them, to form a vessel. Over time, the constellation became identified with ancient Greek myth of Jason and the Argonauts. In his Almagest, Ptolemy described Argo Navis as occupying the portion of the Milky Way between Canis Major and Centaurus, identified stars comprising such details as the "little shield," the "steering-oar," the "mast-holder," and the "stern-ornament", which continued to be reflected in cartographic representations in celestial atlases into the nineteenth century. Another interesting feature of the constellation is that it appeared to be moving backwards against the backdrop of the night sky. Aratus, the Greek poet/historian living in the third century BC, noted this backward progression writing, "Argo by the Great Dog's tail is drawn.
In modern times, Argo Navis was considered unwieldy for scientific purposes due to its enormous size. In his Coelum Australe Stelliferum, published in 1763, the French astronomer Nicolas Louis de Lacaille explained that there were more than a hundred and sixty stars visible to the naked eye in Navis, so he used the set of lowercase and uppercase Latin letters three times on portions of the constellation referred to as "Argûs in carina", "Argûs in puppi", "Argûs in velis". Lacaille replaced Bayer's designations with new ones that followed stellar magnitudes more but used only a single Greek-letter sequence and described the constellation for those stars as "Argûs". Faint non-lettered stars were listed only as in "Argûs"; the final breakup and abolition of Argo Navis was proposed by Sir John Herschel in 1841 and again in 1844. Despite this, the constellation remained in use in parallel with its constituent parts into the 20th century. In 1922, along with the other constellations, it received a three-letter abbreviation: Arg.
The breakup and relegation to a former constellation occurred in 1930 when the IAU defined the 88 modern constellations, formally instituting Carina and Vela. Lacaille's designations were kept in the three separate constellations, so Carina has α, β and ε, Vela has γ and δ, Puppis has ζ, so on; as a result of this breakup, Argo Navis is the only one of the 48 constellations listed by Ptolemy in his Almagest, no longer recognized as a single constellation. In addition, the constellation Pyxis occupies an area near that which in antiquity was considered part of Argo's mast; some authors state that Pyxis was part of the Greek conception of Argo Navis, but magnetic compasses were unknown in ancient Greek times, it does not appear that its stars were included in the original conception. Lacaille considered it a separate constellation, representing one of the modern scientific instruments he placed among the constellations. Pyxis was listed separately, among his 14 new constellations. Lacaille assigned Bayer designations to Pyxis separate from those of Argo, his illustration shows an isolated instrument not related to the figure of the ship.
In 1844, John Herschel suggested formalizing the mast as a new constellation, Malus, to replace Lacaille's Pyxis, but the idea did not catch on. An effort by Edmond Halley to detach the "cloud of mist" at the prow of Argo Navis to form a new constellation named "Robur Carolinum" in honor of his patron, King Charles II, was unsuccessful; the Māori had several names for what was the constellation Argo, including Te Waka-o-Tamarereti, Te Kohi-a-Autahi, Te Kohi. In Vedic astronomy, Indian observers saw Argo Navis as "the Boat." Asterism List of stars in Argo Navis Starry Night Photography: Argo Navis Image Star Tales – Argo Navis Warburg Institute Iconographic Database – Argo
On boats and ships, the keel is either of two parts: a structural element that sometimes resembles a fin and protrudes below a boat along the central line, or a hydrodynamic element. These parts overlap; as the laying down of the keel is the initial step in the construction of a ship, in British and American shipbuilding traditions the construction is dated from this event. Only the ship's launching is considered more significant in its creation; the word can be used as a synecdoche to refer to a complete boat, such as a keelboat. The adjustable centerboard keel traces its roots to the medieval Chinese Song dynasty. Many Song Chinese junk ships had a ballasted and bilge keel that consisted of wooden beams bound together with iron hoops. Maritime technology and the technological know-how allowed Song dynasty ships to be used in naval warfare between the Southern Song Dynasty, the Jin dynasty, the Mongols. A structural keel is the bottom-most structural member; the keel runs from the bow to the stern.
The keel is the first part of a ship's hull to be constructed, laying the keel, or placing the keel in the cradle in which the ship will be built may mark the start time of its construction. Large, modern ships are now built in a series of pre-fabricated, complete hull sections rather than being built around a single keel, so shipbuilding process commences with cutting the first sheet of steel; the most common type of keel is the "flat plate keel", this is fitted in the majority of ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers and smaller ferries. Where grounding is possible, this type of keel is suitable with its massive scantlings, but there is always a problem of the increased draft with no additional cargo capacity. If a double bottom is fitted, the keel is inevitably of the flat plate type, bar keels being associated with open floors, where the plate keel may be fitted. Duct keels are provided in the bottom of some vessels.
These run from the forward engine room bulkhead to the collision bulkhead and are utilized to carry the double bottom piping. The piping is accessible when cargo is loaded; the keel surface on the bottom of the hull gives the ship greater directional stability. In non-sailing hulls, the keel helps the hull to move forward, rather than slipping to the side. In traditional boat building, this is provided by the structural keel, which projects from the bottom of the hull along most or all of its length. In modern construction, the bar keel or flat-plate keel performs the same function. There are many types of fixed keels, including full keels, long keels, fin keels, winged keels, bulb keels, bilge keels among other designs. Deep-draft ships will have a flat bottom and employ only bilge keels, both to aid directional control and to damp rolling motions In sailboats, keels use the forward motion of the boat to generate lift to counteract the leeward force of the wind; the rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion.
A secondary purpose of the keel is to provide ballast. Keels are different from centreboards and other types of foils in that keels are made of heavy materials to provide ballast to stabilize the boat. Keels may be fixed, or non-movable. Retracting keels may pivot or slide upwards to retract, are retracted with a winch due to the weight of the ballast. Since the keel provides far more stability when lowered than when retracted, the amount of sail carried is reduced when sailing with the keel retracted. Types of non-fixed keels include canting keels. Canting keels can be found on racing yachts, such as those competing in the Volvo Ocean Race, they provide more righting moment as the keel moves out to the windward-side of the boat while using less weight. The horizontal distance from the weight to the pivot is increased, which generates a larger righting moment; the word "keel" comes from Old English cēol, Old Norse kjóll, = "ship" or "keel". It has the distinction of being regarded by some scholars as the first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work De Excidio et Conquestu Britanniae, under the spelling cyulae.
Carina is the origin of the term careen. An example of this use is Careening Cove, a suburb of Sydney, where careening was carried out in early colonial days. Coin ceremony Kelson False keel Daggerboard Leeboard Bilgeboard Bruce foil Keelhauling – an archaic maritime punishment Rousmaniere, The Annapolis Book of Seamanship, Simon & Schuster, 1999 Chapman Book of Piloting, Hearst Corporation, 1999 Herreshoff, The Sailor’s Handbook, Little Brown and Company Seidman, The Complete Sailor, International Marine, 1995 Jobson, Sailing Fundamentals, Simon & Schuster, 1987
Jason was an ancient Greek mythological hero, the leader of the Argonauts whose quest for the Golden Fleece featured in Greek literature. He was the son of the rightful king of Iolcos, he was married to the sorceress Medea. He was the great-grandson of the messenger god Hermes, through his mother's side. Jason appeared in various literary works in the classical world of Greece and Rome, including the epic poem Argonautica and the tragedy Medea. In the modern world, Jason has emerged as a character in various adaptations of his myths, such as the 1963 film Jason and the Argonauts and the 2000 TV miniseries of the same name. Jason's father is invariably Aeson. According to various authors, she could be: Alcimede, daughter of Phylacus Polymede, or Polymele, or Polypheme, a daughter of Autolycus Amphinome Theognete, daughter of Laodicus Rhoeo Arne or ScarpheJason was said to have had a younger brother Promachus. By Medea: Alcimenes, murdered by Medea. Thessalus, twin of Alcimenes and king of Iolcus.
Tisander, murdered by Medea Mermeros killed either by the Corinthians or by Medea Pheres, as above Eriopis, their only daughter Medus or Polyxemus, otherwise son of Aegeus Argus seven sons and seven daughtersBy Hypsipyle: Euneus, King of Lemnos and his twin Nebrophonus or Deipylus or Thoas Pelias was power-hungry and sought to gain dominion over all of Thessaly. Pelias was the progeny of a union between their shared mother, the daughter of Salmoneus, the sea god Poseidon. In a bitter feud, he overthrew Aeson, he spared his half-brother for unknown reasons. Aeson's wife Alcimede I had a newborn son named Jason whom she saved from Pelias by having female attendants cluster around the infant and cry as if he were still-born. Fearing that Pelias would notice and kill her son, Alcimede sent him away to be reared by the centaur Chiron,. Pelias, fearing that his ill-gotten kingship might be challenged, consulted an oracle, who warned him to beware of a man wearing only one sandal. Many years Pelias was holding games in honor of Poseidon when the grown Jason arrived in Iolcus, having lost one of his sandals in the river Anauros while helping an old woman to cross.
She blessed him. When Jason entered Iolcus, he was announced as a man wearing only one sandal. Jason, aware Pelias. Pelias replied, "To take my throne, which you shall, you must go on a quest to find the Golden Fleece." Jason accepted this condition. Jason assembled for a number of heroes, known as the Argonauts after their ship, the Argo; the group of heroes included the Boreads who could fly, Philoctetes, Telamon, Orpheus and Pollux, Atalanta and Euphemus. The isle of Lemnos is situated off the Western coast of Asia Minor; the island was inhabited by a race of women. The women had neglected their worship of Aphrodite, as a punishment the goddess made the women so foul in stench that their husbands could not bear to be near them; the men took concubines from the Thracian mainland opposite, the spurned women, angry at Aphrodite, killed all the male inhabitants while they slept. The king, was saved by Hypsipyle, his daughter, who put him out to sea sealed in a chest from which he was rescued; the women of Lemnos lived for a while with Hypsipyle as their queen.
During the visit of the Argonauts the women mingled with the men creating a new "race" called Minyae. Jason fathered twins with the queen. Heracles pressured them to leave, he had not taken part, unusual considering the numerous affairs he had with other women. After Lemnos the Argonauts landed among the Doliones, he forgot to mention what lived there. What lived in the land beyond Bear Mountain were the Gegeines, which are a tribe of Earthborn giants with six arms and wore leather loincloths. While most of the crew went into the forest to search for supplies, the Gegeines saw that few Argonauts were guarding the ship and raided it. Heracles was among those guarding the ship at the time and managed to kill most them before Jason and the others returned. Once some of the other Gegeines were killed and the Argonauts set sail. Sometime after their fight with the Gegeines, they sent some men to find water. Among these men was Heracles' servant Hylas, gathering water while Heracles was out finding some wood to carve a new oar to replace the one that broke.
The nymphs of the stream where Hylas was collecting were attracted to his good looks, pulled him into the stream. Heracles returned to his Labors. Others say that Heracles went to Colchis with the Argonauts, got the Golden Girdle of the Amazons and slew the Stymphalian Birds at that time; the Argonauts departed, landing again at the same spot that night. In the darkness, the Doliones took them for enemies and they started fighting each other; the Argonauts killed many of the Doliones, among them. Cyzicus' wife killed herself; the Argonauts realized their horrible mistake when dawn held a funeral for him. Soon Jason reached the court of Phineus of Salmydessus in Thrace. Zeus had sent the harpies to stea
A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, windsurfers, ice boats, sail-powered land vehicles. Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments—usually in a three- or four-sided shape. A sail provides propulsive force via a combination of lift and drag, depending on its angle of attack—its angle with respect to the apparent wind. Apparent wind is the air velocity experienced on the moving craft and is the combined effect of the true wind velocity with the velocity of the sailing craft. Angle of attack is constrained by the sailing craft's orientation to the wind or point of sail. On points of sail where it is possible to align the leading edge of the sail with the apparent wind, the sail may act as an airfoil, generating propulsive force as air passes along its surface—just as an airplane wing generates lift—which predominates over aerodynamic drag retarding forward motion.
The more that the angle of attack diverges from the apparent wind as a sailing craft turns downwind, the more drag increases and lift decreases as propulsive forces, until a sail going downwind is predominated by drag forces. Sails are unable to generate propulsive force if they are aligned too to the wind. Sails may be attached to a mast, boom or other spar or may be attached to a wire, suspended by a mast, they are raised by a line, called a halyard, their angle with respect to the wind is controlled by a line, called a sheet. In use, they may be designed to be curved in both directions along their surface as a result of their curved edges. Battens may be used to extend the trailing edge of a sail beyond the line of its attachment points. Other non-rotating airfoils that power sailing craft include wingsails, which are rigid wing-like structures, kites that power kite-rigged vessels, but do not employ a mast to support the airfoil and are beyond the scope of this article. Sailing craft employ two types of the square rig and the fore-and-aft rig.
The square rig carries the primary driving sails are carried on horizontal spars, which are perpendicular or square, to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship so rigged is called a square-rigger; the square rig is aerodynamically most efficient. A fore-and-aft rig consists of sails that are set along the line of the keel rather than perpendicular to it. Vessels so rigged. Archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium BCE onwards. Excavations of the Ubaid period in Mesopotamia provides direct evidence of sailing boats. Sails from ancient Egypt are depicted around 3200 BCE, where reed boats sailed upstream against the River Nile's current. Ancient Sumerians used square rigged sailing boats at about the same time, it is believed they established sea trading routes as far away as the Indus valley; the proto-Austronesian words for sail and other rigging parts date to about 3000 BCE when this group began their Pacific expansion.
Greeks and Phoenicians began trading by ship by around 1200 BCE. Triangular fore-and-aft rigs were invented in the Mediterranean as single-yarded lateen sails and independently in the Pacific as the more efficient bi-sparred crab claw sail, continue to be used throughout the world. During the 16th-19th centuries other fore-and-aft sails were developed in Europe, such as the spritsail, gaff rig, genoa and Bermuda rig mainsail, improving the upwind sailing ability of European vessels; the fore-and-aft rig began as a convention of southern Europe and the Mediterranean Sea: the gentle climate made its use practical, in Italy a few centuries before the Renaissance it began to replace the square rig which had dominated all of Europe since the dawn of sea travel. Northern Europeans were resistant to adopting the fore-and-aft rig, despite having seen its use in the course of trade and during the Crusades; the Renaissance changed this: beginning in 1475, their use increased and within a hundred years the fore-and-aft rig was in common use on rivers and in estuaries in Britain, northern France, the Low Countries, though the square rig remained standard for the harsher conditions of the open North Sea as well as for trans-Atlantic sailing.
The lateen sail proved to have better upwind performance for smaller vessels. Aerodynamic forces on sails depend on wind speed and direction and the speed and direction of the craft; the direction that the craft is traveling with respect to the true wind is called the "point of sail". The speed of the craft at a given point of sail contributes to the apparent wind —the wind speed and direction as measured on the moving craft; the apparent wind on the sail creates a total aerodynamic force, which may be resolved into drag—the force component in the direction of the apparent wind—and lift—the force component normal to the apparent wind. Depending on the alignment of the sail with the apparent wind, lift or drag may be the predominant propulsive component. Total aerodynamic force resolves into a forward, driving force—resisted by the medium through or over which the craft is passing —and a lateral force, resisted by the underwater foils, ice runners, or wheels of the sailing craft. For apparent wind angles aligned with the entry point of the sail, the sail acts as an airfoil and lift is the predominant component of propulsion.