Cape of Good Hope
The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula in South Africa. A common misconception is; this misconception was based on the misbelief that the Cape was the dividing point between the Atlantic and Indian Oceans. Contemporary geographic knowledge instead states the southernmost point of Africa is Cape Agulhas about 150 kilometres to the east-southeast; the currents of the two oceans meet at the point where the warm-water Agulhas current meets the cold-water Benguela current and turns back on itself. That oceanic meeting point fluctuates between Cape Point; when following the western side of the African coastline from the equator, the Cape of Good Hope marks the point where a ship begins to travel more eastward than southward. Thus, the first modern rounding of the cape in 1488 by Portuguese explorer Bartolomeu Dias was a milestone in the attempts by the Portuguese to establish direct trade relations with the Far East. Dias called the cape Cabo das Tormentas, the original name of the "Cape of Good Hope".
As one of the great capes of the South Atlantic Ocean, the Cape of Good Hope has long been of special significance to sailors, many of whom refer to it as "the Cape". It is a waypoint on the Cape Route and the clipper route followed by clipper ships to the Far East and Australia, still followed by several offshore yacht races; the term Cape of Good Hope is used in three other ways: It is a section of the Table Mountain National Park, within which the cape of the same name, as well as Cape Point, falls. Prior to its incorporation into the national park, this section constituted the Cape Point Nature Reserve, it was the name of the early Cape Colony established by the Dutch on the Cape Peninsula. Just before the Union of South Africa was formed, the term referred to the entire region that in 1910 was to become the Cape of Good Hope Province. Eudoxus of Cyzicus was a Greek navigator for Ptolemy VIII, king of the Hellenistic Ptolemaic dynasty in Egypt, who found the wreck of a ship in the Indian Ocean that appeared to have come from Gades, rounding the Cape.
When Eudoxus was returning from his second voyage to India, the wind forced him south of the Gulf of Aden and down the coast of Africa for some distance. Somewhere along the coast of East Africa, he found the remains of the ship. Due to its appearance and the story told by the natives, Eudoxus concluded that the ship was from Gades and had sailed anti-clockwise around Africa, passing the Cape and entering the Indian Ocean; this inspired him to attempt a circumnavigation of the continent. Organising the expedition on his own account he set sail from Gades and began to work down the African coast; the difficulties were too great, he was obliged to return to Europe. After this failure he again set out to circumnavigate Africa, his eventual fate is unknown. Although some, such as Pliny, claimed that Eudoxus did achieve his goal, the most probable conclusion is that he perished on the journey. In the 1450 Fra Mauro map, the Indian Ocean is depicted as connected to the Atlantic. Fra Mauro puts the following inscription by the southern tip of Africa, which he names the "Cape of Diab", describing the exploration by a ship from the East around 1420: "Around 1420 a ship, or junk, from India crossed the Sea of India towards the Island of Men and the Island of Women, off Cape Diab, between the Green Islands and the shadows.
It sailed for 40 days in a south-westerly direction without finding anything other than wind and water. According to these people themselves, the ship went some 2,000 miles ahead until - once favourable conditions came to an end - it turned round and sailed back to Cape Diab in 70 days". "The ships called junks that navigate these seas carry four masts or more, some of which can be raised or lowered, have 40 to 60 cabins for the merchants and only one tiller. They can navigate without a compass, because they have an astrologer, who stands on the side and, with an astrolabe in hand, gives orders to the navigator". Fra Mauro explained that he obtained the information from "a trustworthy source", who traveled with the expedition the Venetian explorer Niccolò da Conti who happened to be in Calicut, India at the time the expedition left: "What is more, I have spoken with a person worthy of trust, who says that he sailed in an Indian ship caught in the fury of a tempest for 40 days out in the Sea of India, beyond the Cape of Soffala and the Green Islands towards west-southwest.
Thus one can believe and confirm what is said by both these and those, that they had therefore sailed 4,000 miles". Fra Mauro comments that the account of the expedition, together with the relation by Strabo of the travels of Eudoxus of Cyzicus from Arabia to Gibraltar through the southern Ocean in Antiquity, led him to believe that the Indian Ocean was not a closed sea and that Africa could be circumnavigated by her southern end; this knowledge, together with the map depiction of the African continent encouraged the Portuguese to intensify their effort to round the tip of Africa. I
Edmond Halley, FRS was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena, Halley recorded a transit of Mercury across the Sun, he realised. He used his observations to expand contemporary star maps, he aided in observationally proving Isaac Newton's laws of motion, funded the publication of Newton's influential Philosophiæ Naturalis Principia Mathematica. From his September 1682 observations, he used the laws of motion to compute the periodicity of Halley's Comet in his 1705 Synopsis of the Astronomy of Comets, it was named after him upon its predicted return in 1758. Beginning in 1698, he made sailing expeditions and made observations on the conditions of terrestrial magnetism. In 1718, he discovered the proper motion of the "fixed" stars. Halley was born in east London, his father, Edmond Halley Sr. was a wealthy soap-maker in London. As a child, Halley was interested in mathematics.
He studied at St Paul's School where he developed his initial interest in astronomy, from 1673 at The Queen's College, Oxford. While still an undergraduate, Halley published papers on sunspots. While at the University of Oxford, Halley was introduced to the Astronomer Royal. Influenced by Flamsteed's project to compile a catalog of northern stars, Halley proposed to do the same for the Southern Hemisphere. In 1676, Halley visited the south Atlantic island of Saint Helena and set up an observatory with a large sextant with telescopic sights to catalogue the stars of the Southern Hemisphere. While there he observed a transit of Mercury across the Sun, realised that a similar transit of Venus could be used to determine the absolute size of the Solar System, he returned to England in May 1678. In the following year he went to Danzig on behalf of the Royal Society to help resolve a dispute; because astronomer Johannes Hevelius did not use a telescope, his observations had been questioned by Robert Hooke.
Halley stayed with Hevelius and he observed and verified the quality of Hevelius' observations. In 1679, Halley published the results from his observations on St. Helena as Catalogus Stellarum Australium which included details of 341 southern stars; these additions to contemporary star maps earned him comparison with Tycho Brahe: e.g. "the southern Tycho" as described by Flamsteed. Halley was awarded his M. A. degree at Oxford and elected as a Fellow of the Royal Society at the age of 22. In September 1682 he carried out a series of observations of what became known as Halley's Comet, though his name became associated with it because of his work on its orbit and predicting its return in 1758. In 1686, Halley published the second part of the results from his Helenian expedition, being a paper and chart on trade winds and monsoons; the symbols he used to represent trailing winds still exist in most modern day weather chart representations. In this article he identified solar heating as the cause of atmospheric motions.
He established the relationship between barometric pressure and height above sea level. His charts were an important contribution to the emerging field of information visualisation. Halley spent most of his time on lunar observations, but was interested in the problems of gravity. One problem that attracted his attention was the proof of Kepler's laws of planetary motion. In August 1684, he went to Cambridge to discuss this with Isaac Newton, much as John Flamsteed had done four years earlier, only to find that Newton had solved the problem, at the instigation of Flamsteed with regard to the orbit of comet Kirch, without publishing the solution. Halley asked to see the calculations and was told by Newton that he could not find them, but promised to redo them and send them on which he did, in a short treatise entitled, On the motion of bodies in an orbit. Halley recognised the importance of the work and returned to Cambridge to arrange its publication with Newton, who instead went on to expand it into his Philosophiæ Naturalis Principia Mathematica published at Halley's expense in 1687.
Halley's first calculations with comets were thereby for the orbit of comet Kirch, based on Flamsteed's observations in 1680-1. Although he was to calculate the orbit of the comet of 1682, he was inaccurate in his calculations of the orbit of comet Kirch, they indicated a periodicity of 575 years, thus appearing in the years 531 and 1106, heralding the death of Julius Caesar in a like fashion in −44. It is now known to have an orbital period of circa 10,000 years. In 1691, Halley built a diving bell, a device in which the atmosphere was replenished by way of weighted barrels of air sent down from the surface. In a demonstration and five companions dived to 60 feet in the River Thames, remained there for over an hour and a half. Halley's bell was of little use for practical salvage work, as it was heavy, but he made improvements to it over time extending his underwater exposure time to over 4 hours. Halley suffered one of the earliest recorded cases of middle ear barotrauma; that same year, at a meeting of the Royal Society, Halley introduced a rudimentary working model of a magnetic compass using a liquid-filled housing to damp the swing and wobble of the magnetised needle.
In 1691, Halley sought the post of Savilian Professor of Astronomy at Oxford. While a candidate for the position, Halley faced the animosity of th
The kilogram or kilogramme is the base unit of mass in the International System of Units. Until 20 May 2019, it remains defined by a platinum alloy cylinder, the International Prototype Kilogram, manufactured in 1889, stored in Saint-Cloud, a suburb of Paris. After 20 May, it will be defined in terms of fundamental physical constants; the kilogram was defined as the mass of a litre of water. That was an inconvenient quantity to replicate, so in 1799 a platinum artefact was fashioned to define the kilogram; that artefact, the IPK, have been the standard of the unit of mass for the metric system since. In spite of best efforts to maintain it, the IPK has diverged from its replicas by 50 micrograms since their manufacture late in the 19th century; this led to efforts to develop measurement technology precise enough to allow replacing the kilogram artifact with a definition based directly on physical phenomena, now scheduled to take place in 2019. The new definition is based on invariant constants of nature, in particular the Planck constant, which will change to being defined rather than measured, thereby fixing the value of the kilogram in terms of the second and the metre, eliminating the need for the IPK.
The new definition was approved by the General Conference on Weights and Measures on 16 November 2018. The Planck constant relates a light particle's energy, hence mass, to its frequency; the new definition only became possible when instruments were devised to measure the Planck constant with sufficient accuracy based on the IPK definition of the kilogram. The gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice; the final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram was derived in 1875, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, 4 °C. The kilogram is the only named SI unit with an SI prefix as part of its name; until the 2019 redefinition of SI base units, it was the last SI unit, still directly defined by an artefact rather than a fundamental physical property that could be independently reproduced in different laboratories.
Three other base units and 17 derived units in the SI system are defined in relation to the kilogram, thus its stability is important. The definitions of only eight other named SI units do not depend on the kilogram: those of temperature and frequency, angle; the IPK is used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK; the International Prototype Kilogram was commissioned by the General Conference on Weights and Measures under the authority of the Metre Convention, in the custody of the International Bureau of Weights and Measures who hold it on behalf of the CGPM. After the International Prototype Kilogram had been found to vary in mass over time relative to its reproductions, the International Committee for Weights and Measures recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature.
At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, h. The decision was deferred until 2014. CIPM has proposed revised definitions of the SI base units, for consideration at the 26th CGPM; the formal vote, which took place on 16 November 2018, approved the change, with the new definitions coming into force on 20 May 2019. The accepted redefinition defines the Planck constant as 6.62607015×10−34 kg⋅m2⋅s−1, thereby defining the kilogram in terms of the second and the metre. Since the second and metre are defined in terms of physical constants, the kilogram is defined in terms of physical constants only; the avoirdupois pound, used in both the imperial and US customary systems, is now defined in terms of the kilogram. Other traditional units of weight and mass around the world are now defined in terms of the kilogram, making the kilogram the primary standard for all units of mass on Earth; the word kilogramme or kilogram is derived from the French kilogramme, which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma, a Late Latin term for "a small weight", itself from Greek γράμμα.
The word kilogramme was written into French law in 1795, in the Decree of 18 Germinal, which revised the older system of units introduced by the French National Convention in 1793, where the gravet had been defined as weight of a cubic centimetre of water, equal to 1/1000 of a grave. In the decree of 1795, the term gramme thus replaced gravet, kilogramme replaced grave; the French spelling was adopted in Great Britain when the word was used for the first time in English in 1795, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become by far the more common. UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has been used to mean both kilogram and kilometre. While kilo is acceptable in many generalist texts
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Helium is a chemical element with symbol He and atomic number 2. It is a colorless, tasteless, non-toxic, monatomic gas, the first in the noble gas group in the periodic table, its boiling point is the lowest among all the elements. After hydrogen, helium is the second lightest and second most abundant element in the observable universe, being present at about 24% of the total elemental mass, more than 12 times the mass of all the heavier elements combined, its abundance is similar in Jupiter. This is due to the high nuclear binding energy of helium-4 with respect to the next three elements after helium; this helium-4 binding energy accounts for why it is a product of both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, the vast majority of, formed during the Big Bang. Large amounts of new helium are being created by nuclear fusion of hydrogen in stars. Helium is named for the Greek Titan of the Sun, Helios, it was first detected as an unknown yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet, Captain C. T. Haig, Norman R. Pogson, Lieutenant John Herschel, was subsequently confirmed by French astronomer Jules Janssen.
Janssen is jointly credited with detecting the element along with Norman Lockyer. Janssen recorded the helium spectral line during the solar eclipse of 1868 while Lockyer observed it from Britain. Lockyer was the first to propose; the formal discovery of the element was made in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite. In 1903, large reserves of helium were found in natural gas fields in parts of the United States, by far the largest supplier of the gas today. Liquid helium is used in cryogenics in the cooling of superconducting magnets, with the main commercial application being in MRI scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced. A well-known but minor use is as a lifting gas in airships; as with any gas whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice.
In scientific research, the behavior of the two fluid phases of helium-4 is important to researchers studying quantum mechanics and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero. On Earth it is rare—5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements, as the alpha particles emitted by such decays consist of helium-4 nuclei; this radiogenic helium is trapped with natural gas in concentrations as great as 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Terrestrial helium—a non-renewable resource, because once released into the atmosphere it escapes into space—was thought to be in short supply. However, recent studies suggest that helium produced deep in the earth by radioactive decay can collect in natural gas reserves in larger than expected quantities, in some cases having been released by volcanic activity.
The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India; this line was assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D3 because it was near the known D1 and D2 Fraunhofer line lines of sodium, he concluded. Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος. In 1881, Italian physicist Luigi Palmieri detected helium on Earth for the first time through its D3 spectral line, when he analyzed a material, sublimated during a recent eruption of Mount Vesuvius. On March 26, 1895, Scottish chemist Sir William Ramsay isolated helium on Earth by treating the mineral cleveite with mineral acids. Ramsay was looking for argon but, after separating nitrogen and oxygen from the gas liberated by sulfuric acid, he noticed a bright yellow line that matched the D3 line observed in the spectrum of the Sun.
These samples were identified as helium by Lockyer and British physicist William Crookes. It was independently isolated from cleveite in the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, who collected enough of the gas to determine its atomic weight. Helium was isolated by the American geochemist William Francis Hillebrand prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, attributed the lines to nitrogen, his letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science. In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei by allowing the particles to penetrate the thin glass wall of
Gas is one of the four fundamental states of matter. A pure gas may be made up of individual atoms, elemental molecules made from one type of atom, or compound molecules made from a variety of atoms. A gas mixture would contain a variety of pure gases much like the air. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles; this separation makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric and gravitational fields are considered negligible, as indicated by the constant velocity vectors in the image; the gaseous state of matter is found between the liquid and plasma states, the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention. High-density atomic gases super cooled to low temperatures are classified by their statistical behavior as either a Bose gas or a Fermi gas.
For a comprehensive listing of these exotic states of matter see list of states of matter. The only chemical elements that are stable diatomic homonuclear molecules at STP are hydrogen, nitrogen and two halogens: fluorine and chlorine; when grouped together with the monatomic noble gases – helium, argon, krypton and radon – these gases are called "elemental gases". The word gas was first used by the early 17th-century Flemish chemist Jan Baptist van Helmont, he identified the first known gas other than air. Van Helmont's word appears to have been a phonetic transcription of the Ancient Greek word χάος Chaos – the g in Dutch being pronounced like ch in "loch" – in which case Van Helmont was following the established alchemical usage first attested in the works of Paracelsus. According to Paracelsus's terminology, chaos meant something like "ultra-rarefied water". An alternative story is that Van Helmont's word is corrupted from gahst, signifying a ghost or spirit; this was because certain gases suggested a supernatural origin, such as from their ability to cause death, extinguish flames, to occur in "mines, bottom of wells and other lonely places".
In contrast, French-American historian Jacques Barzun speculated that Van Helmont had borrowed the word from the German Gäscht, meaning the froth resulting from fermentation. Because most gases are difficult to observe directly, they are described through the use of four physical properties or macroscopic characteristics: pressure, number of particles and temperature; these four characteristics were observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies led to a mathematical relationship among these properties expressed by the ideal gas law. Gas particles are separated from one another, have weaker intermolecular bonds than liquids or solids; these intermolecular forces result from electrostatic interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another. Gaseous compounds with polar covalent bonds contain permanent charge imbalances and so experience strong intermolecular forces, although the molecule while the compound's net charge remains neutral.
Transient, randomly induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these intermolecular forces varies within a substance which determines many of the physical properties unique to each gas. A comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion; the drifting smoke particles in the image provides some insight into low-pressure gas behavior. Compared to the other states of matter, gases have low viscosity. Pressure and temperature influence the particles within a certain volume; this variation in particle separation and speed is referred to as compressibility. This particle separation and size influences optical properties of gases as can be found in the following list of refractive indices. Gas particles spread apart or diffuse in order to homogeneously distribute themselves throughout any container; when observing a gas, it is typical to specify a frame of length scale.
A larger length scale corresponds to a global point of view of the gas. This region must be sufficient in size to contain a large sampling of gas particles; the resulting statistical analysis of this sample size produces the "average" behavior of all the gas particles within the region. In contrast, a smaller length scale corresponds to a particle point of view. Macroscopically, the gas characteristics measured are either in terms of the gas particles themselves or their surroundings. For example, Robert Boyle studied pneumatic chemistry for a small portion of his career. One of his experiments related the macroscopic properties of volume of a gas, his experiment used a J-tube manometer which looks like a test tube in the shape of the letter J. Boyle trapped an inert gas in the closed end of the test tube with a column of mercury, thereby ma
Ursa Major is a constellation in the northern sky, whose associated mythology dates back into prehistory. Its Latin name means "greater she-bear", standing as a reference to and in direct contrast with nearby Ursa Minor, the lesser bear. In antiquity, it was one of the original 48 constellations listed by Ptolemy, is now the third largest constellation of the 88 modern constellations. Ursa Major is known from the asterism of its main seven bright stars comprising the "Big Dipper", "the Wagon", "Charles's Wain" or "the Plough", with its stellar configuration mimicking the shape of the "Little Dipper"; the general constellation outline significantly features in numerous world cultures, is used as a symbol of the north. E.g. as the flag of Alaska. The asterism's two brightest stars, named Dubhe and Merak, can be used as the navigational pointer towards the place of the current northern pole star, Polaris in Ursa Minor. Ursa Major is visible throughout the year from most of the northern hemisphere, appears circumpolar above the mid-northern latitudes.
From southern temperate latitudes, the main asterism is invisible, but the southern parts of the constellation can still be viewed. Appearing in the northern sky, Ursa Major occupies a large area covering 1279.66 square degrees or 3.10% of the total sky, making it the third largest constellations in the night sky. Eugène Delporte in 1930, who set the official International Astronomical Union constellation boundaries, formed a 28-sided irregular polygon, which according to the equatorial coordinate system, stretches between the right ascension coordinates of 08h 08.3m and 14h 29.0m and the declination coordinates of +28.30° and +73.14°. Ursa Major borders eight other constellations: Draco to the north and northeast, Boötes to the east, Canes Venatici to the east and southeast, Coma Berenices to the southeast and Leo Minor to the south, Lynx to the southwest and Camelopardalis to the northwest; the three-letter constellation abbreviation'UMa' was adopted by the IAU in 1922. The "Big Dipper" is an asterism within Ursa Major composed of seven bright stars that together comprise one of the best-known patterns in the sky.
Like many of its common names allude to, its shape is said to resemble either a ladle, an agricultural plough or wagon. Starting with the "ladle" portion of the dipper and extending clockwise through the handle, these stars are the following: α Ursae Majoris, known by the Arabic name Dubhe, which at a magnitude of 1.79 is the 35th-brightest star in the sky and the second-brightest of Ursa Major. Β Ursae Majoris, called Merak, with a magnitude of 2.37. Γ Ursae Majoris, known as either Phecda or Phad, with a magnitude of 2.44. Δ Ursae Majoris, or Megrez, meaning "root of the tail," referring to its location as the intersection of the body and tail of the bear. Ε Ursae Majoris, known as Alioth, a name which refers not to a bear but to a "black horse," the name corrupted from the original and mis-assigned to the named Alcor, the naked-eye binary companion of Mizar. Alioth is the brightest star of Ursa Major and the 33rd-brightest in the sky, with a magnitude of 1.76. It is the brightest of the "peculiar A stars," magnetic stars whose chemical elements are either depleted or enhanced, appear to change as the star rotates.
Ζ Ursae Majoris, the second star in from the end of the handle of the Big Dipper, the constellation's fourth-brightest star. Mizar, which means "girdle," forms a famous double star, with its optical companion Alcor, the two of which were termed the "horse and rider" by the Arabs; the ability to resolve the two stars with the naked eye is quoted as a test of eyesight, although people with quite poor eyesight can see the two stars. Η Ursae Majoris, known as either Alkaid or Benetnash, both meaning the "end of the tail." With a magnitude of 1.85, Alkaid is the third-brightest star of Ursa Major. Except for Dubhe and Alkaid, the stars of the Big Dipper all have proper motions heading toward a common point in Sagittarius. A few other such stars have been identified, together they are called the Ursa Major Moving Group; the stars Merak and Dubhe are known as the "pointer stars" because they are helpful for finding Polaris known as the North Star or Pole Star. By visually tracing a line from Merak through Dubhe and continuing for 5 units, one's eye will land on Polaris indicating true north.
Another asterism known as the "Three Leaps of the Gazelle" is recognized in Arab culture, a series of three pairs of stars found along the southern border of the constellation. W Ursae Majoris is the prototype of a class of contact binary variable stars, ranges between 7.75m and 8.48m. 47 Ursae Majoris is a Sun-like star with a three-planet system. 47 Ursae Majoris b, discovered in 1996, orbits every 1078 days and is 2.53 times the mass of Jupiter. 47 Ursae Majoris c, discovered in 2001, orbits every 2391 days and is 0.54 times the