1.
Theia (planet)
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According to the hypothesis, Theia was an Earth trojan about the size of Mars, with diameter of about 6,000 km. Models of the impact propose that Theias debris gathered around Earth to form the early Moon, some scientists think that the material thrown into orbit originally formed two moons that later merged to form the single moon we know today. The Theia hypothesis also explains why Earths core is larger than would be expected for a body its size, according to the hypothesis, Theias core and mantle mixed with Earths. Analysis of lunar rocks, published in 2016, suggests that the impact may have been a direct hit, Theia is thought to have orbited in the L4 or L5 configuration presented by the Earth–Sun system, where it would tend to remain. In that case, it would have grown, potentially to a size comparable to Mars, gravitational perturbations by Venus could have eventually put it onto a collision course with the Earth. An alternative name, Orpheus, is also popular, such accounts assumed that Theia striking the proto-Earth head-on would have led to the destruction of both planets, creating a short-lived second asteroid belt between the orbits of Venus and Mars. In contrast, evidence published in January 2016 suggests that the impact was indeed a head-on collision, the lunar rock samples retrieved by Apollo astronauts were found to be very similar in composition to Earths crust, and so were likely removed from Earth in some violent event
2.
Moon
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The Moon is an astronomical body that orbits planet Earth, being Earths only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, following Jupiters satellite Io, the Moon is second-densest satellite among those whose densities are known. The average distance of the Moon from the Earth is 384,400 km, the Moon is thought to have formed about 4.51 billion years ago, not long after Earth. It is the second-brightest regularly visible celestial object in Earths sky, after the Sun and its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art. The Moons gravitational influence produces the ocean tides, body tides, and this matching of apparent visual size will not continue in the far future. The Moons linear distance from Earth is currently increasing at a rate of 3.82 ±0.07 centimetres per year, since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft. The usual English proper name for Earths natural satellite is the Moon, the noun moon is derived from moone, which developed from mone, which is derived from Old English mōna, which ultimately stems from Proto-Germanic *mǣnōn, like all Germanic language cognates. Occasionally, the name Luna is used, in literature, especially science fiction, Luna is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon. The principal modern English adjective pertaining to the Moon is lunar, a less common adjective is selenic, derived from the Ancient Greek Selene, from which is derived the prefix seleno-. Both the Greek Selene and the Roman goddess Diana were alternatively called Cynthia, the names Luna, Cynthia, and Selene are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana is connected to dies meaning day, several mechanisms have been proposed for the Moons formation 4.51 billion years ago, and some 60 million years after the origin of the Solar System. These hypotheses also cannot account for the angular momentum of the Earth–Moon system. This hypothesis, although not perfect, perhaps best explains the evidence, eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists, You have eighteen months. Go back to your Apollo data, go back to computer, do whatever you have to. Dont come to our conference unless you have something to say about the Moons birth, at the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular. Afterward there were only two groups, the giant impact camp and the agnostics. Giant impacts are thought to have been common in the early Solar System, computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth–Moon system
3.
Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
4.
Hadean
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The Hadean is a geologic eon of the Earth predating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, the geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the Priscoan period, other, older texts simply refer to the eon as the Pre-Archean. Nonetheless, in 2015, traces of carbon minerals interpreted as remains of life were found in 4. 1-billion-year-old rocks in Western Australia. Since few geological traces of this eon remain on Earth, there is no official subdivision, however, the Lunar geologic timescale embraces several major divisions relating to the Hadean, so these are sometimes used in an informal sense to refer to the same periods of time on Earth. In 2010, a scale was proposed that includes the addition of the Chaotian and Prenephelean Eons preceding the Hadean. The Paleohadean era consists of the Hephaestean and the Jacobian periods, the Mesohadean is divided into the Canadian and the Procrustean periods. The Neohadean is divided into the Acastan and the Promethean periods, as of February 2017, this has not been adopted by the IUGS. In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada, and Western Australia. The oldest dated zircon crystals, enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia, date to 4.404 ±0.008 Ga. This zircon is an outlier, with the oldest consistently-dated zircon falling closer to 4.35 Ga—around 200 million years after the hypothesized time of the Earths formation. A sizeable quantity of water would have been in the material formed the Earth. Water molecules would have escaped Earths gravity more easily when it was less massive during its formation, hydrogen and helium are expected to continually escape due to atmospheric escape. Part of the ancient planet is theorized to have been disrupted by the impact created the Moon. Earths present composition suggests that there was not complete remelting as it is difficult to completely melt, however, a fair fraction of material should have been vaporized by this impact, creating a rock vapor atmosphere around the young planet. The rock vapor would have condensed within two years, leaving behind hot volatiles which probably resulted in a heavy CO2 atmosphere with hydrogen. Liquid water oceans existed despite the temperature of 230 °C because at an atmospheric pressure of above 27 atmospheres, caused by the heavy CO2 atmosphere. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared
5.
Theia
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In Greek mythology, Theia, also called Euryphaessa wide-shining, is a Titaness. Her brother/ consort is Hyperion, a Titan and god of the sun, and together they are the parents of Helios, Selene, the name Theia alone means simply goddess or divine, Theia Euryphaessa brings overtones of extent and brightness. Hesiods Theogony gives her an equally primal origin, said to be the eldest daughter of Gaia, robert Graves also relates that later Theia is referred to as the cow-eyed Euryphaessa who gave birth to Helios in myths dating to Classical Antiquity. Theias alternate name Euryphaessa has been adopted for a species of Australian leafhoppers Dayus euryphaessa, Greek mythology in popular culture Smith, William, Dictionary of Greek and Roman Biography and Mythology, London
6.
Hypothesis
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A hypothesis is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the scientific theories. Even though the hypothesis and theory are often used synonymously. A working hypothesis is a provisionally accepted hypothesis proposed for further research, P is the assumption in a What If question. Remember, the way that you prove an implication is by assuming the hypothesis, --Philip Wadler In its ancient usage, hypothesis referred to a summary of the plot of a classical drama. The English word hypothesis comes from the ancient Greek ὑπόθεσις word hupothesis, in Platos Meno, Socrates dissects virtue with a method used by mathematicians, that of investigating from a hypothesis. In this sense, hypothesis refers to an idea or to a convenient mathematical approach that simplifies cumbersome calculations. In common usage in the 21st century, a hypothesis refers to an idea whose merit requires evaluation. For proper evaluation, the framer of a hypothesis needs to define specifics in operational terms, a hypothesis requires more work by the researcher in order to either confirm or disprove it. In due course, a hypothesis may become part of a theory or occasionally may grow to become a theory itself. Normally, scientific hypotheses have the form of a mathematical model, in entrepreneurial science, a hypothesis is used to formulate provisional ideas within a business setting. The formulated hypothesis is then evaluated where either the hypothesis is proven to be true or false through a verifiability- or falsifiability-oriented Experiment, any useful hypothesis will enable predictions by reasoning. It might predict the outcome of an experiment in a setting or the observation of a phenomenon in nature. The prediction may also invoke statistics and only talk about probabilities, other philosophers of science have rejected the criterion of falsifiability or supplemented it with other criteria, such as verifiability or coherence. The scientific method involves experimentation, to test the ability of some hypothesis to adequately answer the question under investigation. In contrast, unfettered observation is not as likely to raise unexplained issues or open questions in science, a thought experiment might also be used to test the hypothesis as well. In framing a hypothesis, the investigator must not currently know the outcome of a test or that it remains reasonably under continuing investigation, only in such cases does the experiment, test or study potentially increase the probability of showing the truth of a hypothesis
7.
Planetary core
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The planetary core consists of the innermost layer of a planet, which may be composed of solid and liquid layers. Cores of specific planets may be solid or entirely liquid. In the Solar System, core size can range from about 20% to 85% of a planets radius. Gas giants also have cores, though the composition of these are still a matter of debate and range in composition from traditional stony/iron. In 1798, Henry Cavendish calculated the density of the earth to be 5.48 times the density of water. The first detection of Earths core occurred in 1906 by Richard Dixon Oldham upon discovery of the P-wave shadow zone, by 1936 seismologists had determined the size of the overall core as well as the boundary between the fluid outer core and the solid inner core. Planetary systems form from a disk of dust and gas that accrete rapidly into planetesimals around 10 km in diameter. From here gravity takes over to produce Moon to Mars sized planetary embryos, Jupiter and Saturn most likely formed around previously existing rocky and/or icy bodies, rendering these previous primordial planets into gas-giant cores. This is the core accretion model of planet formation. Planetary differentiation is broadly defined as the development from one thing to many things, the hafnium-182/tungsten-182 isotopic system has a half-life of 9 million years, and is approximated as an extinct system after 45 million years. Hafnium is an element and tungsten is siderophile element. The observed Hf/W ratios in iron meteorites constrain metal segregation to under 5 million years, several factors control segregation of a metal core including the crystallization of perovskite. Crystallization of perovskite in a magma ocean is an oxidation process. Impacts between planet-sized bodies in the early Solar System are important aspects in the formation and growth of planets, the giant impact hypothesis states that an impact between a theoretical Mars-sized planet Theia and the early Earth formed the modern Earth and moon. During this impact the majority of the iron from Theia and the Earth became incorporated into the Earths core, core merging between the proto-mars and another differentiated planetoid could have been as fast as 1000 years or as slow as 300,000 years. Earths core contains half the Earths vanadium and chromium, and may contain considerable niobium and tantalum, Earths core is depleted in germanium and gallium. Sulfur is strongly siderophile and only moderately volatile and depleted in the silicate earth, by similar argument, phosphorus may be present up to 0.2 weight %. Hydrogen and carbon, however, are volatile and thus would have been lost during early accretion
8.
Debris disk
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A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right, debris disks have been found around both mature and young stars, as well as at least one debris disk in orbit around an evolved neutron star. Younger debris disks can constitute a phase in the formation of a planetary system following the protoplanetary disk phase and they can also be produced and maintained as the remnants of collisions between planetesimals, otherwise known as asteroids and comets. By 2001, over 900 candidate stars had been found to possess a debris disk and they are usually discovered by examining the star system in infrared light and looking for an excess of radiation beyond that emitted by the star. This excess is inferred to be radiation from the star that has been absorbed by the dust in the disk, debris disks are often described as massive analogs to the debris in the Solar System. Most known debris disks have radii of 10–100 astronomical units, they resemble the Kuiper belt in the Solar System, some debris disks contain a component of warmer dust located within 10 AU from the central star. This dust is called exozodiacal dust by analogy to zodiacal dust in the Solar System. In 1984 a debris disk was detected around the star Vega using the IRAS satellite, initially this was believed to be a protoplanetary disk, but it is now thought to be a debris disk due to the lack of gas in the disk and the age of the star. Subsequently irregularities have been found in the disk, which may be indicative of the presence of planetary bodies, similar discoveries of debris disks were made around the stars Fomalhaut and Beta Pictoris. The nearby star 55 Cancri, a system that is known to contain five planets, was reported to also have a debris disk. Structures in the disk around Epsilon Eridani suggest perturbations by a planetary body in orbit around that star. During the formation of a Sun-like star, the passes through the T-Tauri phase during which it is surrounded by a disk-shaped nebula. Out of this material are formed planetesimals, which can undergo a process to form planets. The nebula continues to orbit the star for a period of 1–20 million years until it is cleared out by radiation pressure. Additional dust may then be generated about the star by collisions between the planetesimals, which forms a disk out of the resulting debris. At some point during their lifetime, at least 45% of these stars are surrounded by a debris disk, repeated collisions can cause a disk to persist for much of the lifetime of a star. Typical debris disks contain small grains 1–100 μm in size, collisions will grind down these grains to sub-micrometre sizes, which will be removed from the system by radiation pressure from the host star. In very tenuous disks like the ones in the Solar System, both processes limit the lifetime of the disk to 10 Myr or less
9.
Formation and evolution of the Solar System
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The formation of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. This model, known as the hypothesis, was first developed in the 18th century by Emanuel Swedenborg, Immanuel Kant. Its subsequent development has interwoven a variety of disciplines including astronomy, physics, geology. Since the dawn of the age in the 1950s and the discovery of extrasolar planets in the 1990s. The Solar System has evolved considerably since its initial formation, many moons have formed from circling discs of gas and dust around their parent planets, while other moons are thought to have formed independently and later been captured by their planets. Still others, such as Earths Moon, may be the result of giant collisions, collisions between bodies have occurred continually up to the present day and have been central to the evolution of the Solar System. The positions of the planets often shifted due to gravitational interactions and this planetary migration is now thought to have been responsible for much of the Solar Systems early evolution. In the far distant future, the gravity of passing stars will gradually reduce the Suns retinue of planets, some planets will be destroyed, others ejected into interstellar space. Ultimately, over the course of tens of billions of years, the first step toward a theory of Solar System formation and evolution was the general acceptance of heliocentrism, which placed the Sun at the centre of the system and the Earth in orbit around it. This concept had developed for millennia, but was not widely accepted until the end of the 17th century, the first recorded use of the term Solar System dates from 1704. The most significant criticism of the hypothesis was its apparent inability to explain the Suns relative lack of momentum when compared to the planets. However, since the early 1980s studies of stars have shown them to be surrounded by cool discs of dust and gas, exactly as the nebular hypothesis predicts. Understanding of how the Sun is expected to continue to evolve required an understanding of the source of its power, in 1935, Eddington went further and suggested that other elements also might form within stars. Fred Hoyle elaborated on this premise by arguing that evolved stars called red giants created many elements heavier than hydrogen, when a red giant finally casts off its outer layers, these elements would then be recycled to form other star systems. The nebular hypothesis says that the Solar System formed from the collapse of a fragment of a giant molecular cloud. The cloud was about 20 parsec across, while the fragments were roughly 1 parsec across, the further collapse of the fragments led to the formation of dense cores 0. 01–0.1 pc in size. One of these fragments formed what became the Solar System. The remaining 2% of the mass consisted of elements that were created by nucleosynthesis in earlier generations of stars
10.
Planetary differentiation
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Such a process tends to create a core and mantle. Sometimes a chemically distinct crust forms on top of the mantle, the process of planetary differentiation has occurred on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites. When the Sun ignited in the nebula, hydrogen, helium. The solar wind and radiation pressure forced these low-density materials away from the Sun, rocks, and the elements comprising them, were stripped of their early atmospheres, but themselves remained, to accumulate into protoplanets. Protoplanets had higher concentrations of radioactive elements early in their history, heating due to radioactivity, impacts, and gravitational pressure melted parts of protoplanets as they grew toward being planets. In melted zones, it was possible for denser materials to sink towards the center, the compositions of some meteorites show that differentiation also took place in some asteroids, that are parental bodies for meteoroids. The short-lived radioactive isotope 26Al was probably the source of heat. When protoplanets accrete more material, the energy of impact causes local heating, in addition to this temporary heating, the gravitational force in a sufficiently large body creates pressures and temperatures which are sufficient to melt some of the materials. This allows chemical reactions and density differences to mix and separate materials, on Earth, a large piece of molten iron is sufficiently denser than continental crust material to force its way down through the crust to the mantle. In the outer Solar System a similar process may take place but with lighter materials, they may be such as methane, water as liquid or ice. High-density materials tend to sink through lighter materials and this tendency is affected by the relative structural strengths, but such strength is reduced at temperatures where both materials are plastic or molten. Iron, the most common element that is likely to form a dense molten metal phase. With it, many siderophile elements also travel downward, however, not all heavy elements make this transition as some chalcophilic heavy elements bind into low-density silicate and oxide compounds, which differentiate in the opposite direction. Even lighter still are the watery liquid hydrosphere and the gaseous, lighter materials tend to rise through material with a higher density. They may take on dome-shaped forms called diapirs when doing so, on Earth, salt domes are salt diapirs in the crust which rise through surrounding rock. Diapirs of molten low-density silicate rocks such as granite are abundant in the Earths upper crust, the hydrated, low-density serpentinite formed by alteration of mantle material at subduction zones can also rise to the surface as diapirs. Other materials do likewise, a low-temperature, near-surface example is provided by mud volcanos and it is also high in uranium and thorium. Magma in the Earth is produced by melting of a source rock
11.
Volatility (chemistry)
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In chemistry and physics, volatility is quantified by the tendency of a substance to vaporize. Volatility is directly related to a vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a vapor pressure. The vapor pressure of a substance is the pressure at which its gas phase is in equilibrium with its condensed phases and it is a measure of the tendency of molecules and atoms to escape from a liquid or a solid. The higher the pressure of a liquid at a given temperature, the higher the volatility. The vapor pressure chart displays the vapor pressures dependency for a variety of liquids as a function of temperature, for example, at any given temperature, chloromethane has the highest vapor pressure of any of the liquids in the chart. It also has the lowest normal boiling point, which is where the pressure curve intersects the horizontal pressure line of one atmosphere of absolute vapor pressure
12.
Venus
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Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period of any planet in the Solar System and it is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the sky after the Moon, reaching an apparent magnitude of −4.6. Because Venus orbits within Earths orbit it is a planet and never appears to venture far from the Sun. Venus is a planet and is sometimes called Earths sister planet because of their similar size, mass, proximity to the Sun. It is radically different from Earth in other respects and it has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the surface is 92 times that of Earth. Venus is by far the hottest planet in the Solar System, with a surface temperature of 735 K. Venus is shrouded by an layer of highly reflective clouds of sulfuric acid. It may have had water oceans in the past, but these would have vaporized as the temperature rose due to a greenhouse effect. The water has probably photodissociated, and the hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Venuss surface is a dry desertscape interspersed with rocks and is periodically resurfaced by volcanism. As one of the brightest objects in the sky, Venus has been a fixture in human culture for as long as records have existed. It has been sacred to gods of many cultures, and has been a prime inspiration for writers and poets as the morning star. Venus was the first planet to have its motions plotted across the sky, as the closest planet to Earth, Venus has been a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft, Venuss thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more missions. Venus is one of the four planets in the Solar System
13.
George Darwin
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Sir George Howard Darwin KCB FRS FRSE was an English barrister, eugenicist, astronomer, and mathematician. George Darwin was born at Down House, Kent, the son and fifth child of Charles Darwin. He graduated as second wrangler in 1868, when he was placed second for the Smiths Prize and was appointed to a college fellowship. He earned his M. A. in 1871 and he was admitted to the bar in 1872, but returned to science. He was elected a Fellow of the Royal Society in June 1879 and won their Royal Medal in 1884 and he delivered their Bakerian Lecture in 1891 on the subject of tidal prediction. In 1883 Darwin became Plumian Professor of Astronomy and Experimental Philosophy at the University of Cambridge and he studied tidal forces involving the Sun, Moon, and Earth, and formulated the fission theory of Moon formation. Darwin was a Fellow of the Royal Astronomical Society and won the Gold Medal of the RAS in 1892, from 1899–1901 he served as President of the RAS. The RAS founded a prize lectureship in 1984 and named it the George Darwin Lectureship in Darwins honour and he was an invited speaker in the International Congress of Mathematicians 1908, Rome on the topic of Mechanics, Physical Mathematics, Astronomy. As President of the Cambridge Philosophical Society, he gave the Introductory Address to the Congress in 1912 on the character of pure. George and Maud Darwin bought Newnham Grange, Cambridge in 1885, the Darwins extensively remodelled the house. Since 1962 the Grange has been part of Darwin College, Cambridge, Darwin married Martha du Puy, the daughter of Charles du Puy of Philadelphia, in 1884, his wife was a member of the Ladies Dining Society in Cambridge, with 11 other members. She died on 6 February 1947 and they had three sons and two daughters, Gwen Raverat, artist. Sir Charles Galton Darwin, physicist and applied mathematics, margaret Elizabeth Darwin, married Sir Geoffrey Keynes. William Robert Darwin Leonard Darwin Tides, Scientific papers, Figures of equilibrium of rotating liquid and geophysical investigations. Scientific papers, Periodic orbits and miscellaneous papers, Scientific papers Supplementary volume, containing biographical memoirs by Sir Francis Darwin and Professor E. W. Brown, lectures on Hills lunar theory, etc. The Scientific Papers of Sir George Darwin, Cambridge University Press On Beneficial Restrictions to Liberty of Marriage, The Contemporary Review, Vol. XXII, June/November 1873. Commodities Versus Labour, The Contemporary Review, Vol. XXII, the Birth of a Satellite Harpers Monthly Magazine, December 1903, pages 124 to 130. George Howard Darwin at the Mathematics Genealogy Project The Genesis of Double Stars – by George Darwin, from A. C. Sewards Darwin, archival material relating to George Darwin
14.
Centrifugal force
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In Newtonian mechanics, the centrifugal force is an inertial force directed away from the axis of rotation that appears to act on all objects when viewed in a rotating reference frame. When they are analyzed in a coordinate system. The term has also been used for the force that is a reaction to a centripetal force. The centrifugal force is an outward force apparent in a reference frame. All measurements of position and velocity must be relative to some frame of reference. An inertial frame of reference is one that is not accelerating, the use of an inertial frame of reference, which will be the case for all elementary calculations, is often not explicitly stated but may generally be assumed unless stated otherwise. In terms of a frame of reference, the centrifugal force does not exist. All calculations can be performed using only Newtons laws of motion, in its current usage the term centrifugal force has no meaning in an inertial frame. In an inertial frame, an object that has no acting on it travels in a straight line. When measurements are made with respect to a reference frame, however. If it is desired to apply Newtons laws in the frame, it is necessary to introduce new, fictitious. Consider a stone being whirled round on a string, in a horizontal plane, the only real force acting on the stone in the horizontal plane is the tension in the string. There are no forces acting on the stone so there is a net force on the stone in the horizontal plane. In an inertial frame of reference, were it not for this net force acting on the stone, in order to keep the stone moving in a circular path, this force, known as the centripetal force, must be continuously applied to the stone. As soon as it is removed the stone moves in a straight line, in this inertial frame, the concept of centrifugal force is not required as all motion can be properly described using only real forces and Newtons laws of motion. In a frame of reference rotating with the stone around the axis as the stone. However, the tension in the string is still acting on the stone, if Newtons laws were applied in their usual form, the stone would accelerate in the direction of the net applied force, towards the axis of rotation, which it does not do. With this new the net force on the stone is zero, with the addition of this extra inertial or fictitious force Newtons laws can be applied in the rotating frame as if it were an inertial frame
15.
Apollo program
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Five subsequent Apollo missions also landed astronauts on the Moon, the last in December 1972. In these six spaceflights, twelve men walked on the Moon, Apollo ran from 1961 to 1972, with the first manned flight in 1968. It achieved its goal of manned lunar landing, despite the setback of a 1967 Apollo 1 cabin fire that killed the entire crew during a prelaunch test. After the first landing, sufficient flight hardware remained for nine follow-on landings with a plan for extended lunar geological and astrophysical exploration, Budget cuts forced the cancellation of three of these. The crew returned to Earth safely by using the Lunar Module as a lifeboat for these functions, Apollo set several major human spaceflight milestones. It stands alone in sending manned missions beyond low Earth orbit, Apollo 8 was the first manned spacecraft to orbit another celestial body, while the final Apollo 17 mission marked the sixth Moon landing and the ninth manned mission beyond low Earth orbit. The program returned 842 pounds of rocks and soil to Earth, greatly contributing to the understanding of the Moons composition. The program laid the foundation for NASAs subsequent human spaceflight capability, Apollo also spurred advances in many areas of technology incidental to rocketry and manned spaceflight, including avionics, telecommunications, and computers. The Apollo program was conceived during the Eisenhower administration in early 1960, while the Mercury capsule could only support one astronaut on a limited Earth orbital mission, Apollo would carry three astronauts. Possible missions included ferrying crews to a station, circumlunar flights. The program was named after the Greek god of light, music, and the sun by NASA manager Abe Silverstein, who later said that I was naming the spacecraft like Id name my baby. Silverstein chose the name at home one evening, early in 1960, in July 1960, NASA Deputy Administrator Hugh L. Dryden announced the Apollo program to industry representatives at a series of Space Task Group conferences. Preliminary specifications were laid out for a spacecraft with a mission module cabin separate from the module. On August 30, a feasibility study competition was announced, and on October 25, meanwhile, NASA performed its own in-house spacecraft design studies led by Maxime Faget, to serve as a gauge to judge and monitor the three industry designs. In November 1960, John F. Kennedy was elected president after a campaign that promised American superiority over the Soviet Union in the fields of space exploration and missile defense. Beyond military power, Kennedy used aerospace technology as a symbol of prestige, pledging to make the US not first but, first and, first if. Despite Kennedys rhetoric, he did not immediately come to a decision on the status of the Apollo program once he became president and he knew little about the technical details of the space program, and was put off by the massive financial commitment required by a manned Moon landing. On April 12,1961, Soviet cosmonaut Yuri Gagarin became the first person to fly in space, Kennedy was circumspect in his response to the news, refusing to make a commitment on Americas response to the Soviets
16.
Roscosmos
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The Roscosmos State Corporation for Space Activities, commonly known as Roscosmos, is the governmental body responsible for the space science program of Russia and general aerospace research. The Corporation was established on the basis of the now-defunct Federal Space Agency on December 28,2015, Roscosmos was previously known as the Russian Aviation and Space Agency. The headquarters of Roscosmos are located in Moscow, while the main Mission Control space center is located in the city of Korolev. The Yuri Gagarin Cosmonaut Training Center is in Star City, the Launch facilities used are Baikonur Cosmodrome in Kazakhstan, and Vostochny Cosmodrome being built in the Russian Far East in Amur Oblast. The current Director since January 2015 is Igor Komarov, in 2015 the Russian government merged Roscosmos with the United Rocket and Space Corporation, the re-nationalized Russian space industry, to create the Roscosmos State Corporation. The Soviet space program did not have central executive agencies, instead, its organizational architecture was multi-centered, it was the design bureaus and the council of designers that had the most say, not the political leadership. The creation of a central agency after the separation of Russia from the Soviet Union was therefore a new development, Russian Space Agency was formed on February 25,1992, by a decree of President Yeltsin. Yuri Koptev, who had worked with designing Mars landers at NPO Lavochkin. In the early years, the agency suffered from lack of authority as the design bureaus fought to protect their own spheres of operation. For example, the decision to keep Mir in operation beyond 1999 was not taken by the agency, instead, another example is that the decision to develop the new Angara rocket was rather a function of Khrunichevs ability to attract resources than a conscious long-term decision by the agency. The 1990s saw serious financial problems because of decreased cash flow and this resulted in Roscosmos leading role in commercial satellite launches and space tourism. In March 2004, director Yuri Koptev was replaced by Anatoly Perminov, the Russian economy boomed throughout 2005 from high prices for exports, such as oil and gas, the outlook for future funding in 2006 appeared more favorable. The budget for 2006 was as high as 25 billion rubles, under the current 10-year budget approved, the budget of the Space Agency shall increase 5–10% per year, providing the space agency with a constant influx of money. In addition to the budget, Roscosmos plans to have over 130 billion rubles flowing into its budget by other means, such as industry investments and it is around the time US-based The Planetary Society entered a partnership with Roscosmos. In 2011, the government spent 115 billion rubles in the space programs. The proposed project core budget for 2013 to be around 128.3 billion rubles, the budget for the whole space program is,169.8 billion rubles. By 2015, the amount of the budget can be increased to 199.2 billion rubles, priorities of the Russian space program include the new Angara rocket family and development of new communications, navigation and remote Earth sensing spacecraft. The GLONASS global navigation system has for many years been one of the top priorities and has been given its own budget line in the federal space budget
17.
Lunar Laser Ranging experiment
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The ongoing Lunar Laser Ranging Experiment measures the distance between Earth and the Moon using laser ranging. Lasers on Earth are aimed at retroreflectors planted on the Moon during the Apollo program, the time for the reflected light to return is measured. Similar measurements were obtained later the year by a Soviet team at the Crimean Astrophysical Observatory using a Q-switched ruby laser. Successful lunar laser range measurements to the retroreflectors were first reported by the 3, the unmanned Soviet Lunokhod 1 and Lunokhod 2 rovers carried smaller arrays. Lunokhod 2s array continues to return signals to Earth, the Lunokhod arrays suffer from decreased performance in direct sunlight—a factor considered in reflector placement during the Apollo missions. The Apollo 15 array is three times the size of the left by the two earlier Apollo missions. Its size made it the target of three-quarters of the measurements taken in the first 25 years of the experiment. The distance to the Moon is calculated using this equation, distance = /2 In actuality. Nonetheless, the Earth–Moon distance has been measured with increasing accuracy for more than 35 years, the distance continually changes for a number of reasons, but averages 385,000.6 km. At the Moons surface, the beam is about 6.5 kilometers wide, the reflected light is too weak to see with the human eye. Out of 1017 photons aimed at the reflector, only one is received back on Earth every few seconds and they can be identified as originating from the laser because the laser is highly monochromatic. This is one of the most precise measurements ever made. As of 2002, work is progressing on increasing the accuracy of the Earth–Moon measurements to near millimeter accuracy, Lunar laser ranging measurement data is available from the Paris Observatory Lunar Analysis Center, and the active stations. Some of the findings of this experiment are, The Moon is spiraling away from Earth at a rate of 3.8 cm per year. This rate has been described as anomalously high, the Moon probably has a liquid core of about 20% of the Moons radius. The universal force of gravity is very stable, the experiments have constrained the change in Newtons gravitational constant G to ×10−13 per year. The likelihood of any Nordtvedt effect has been ruled out to high precision, einsteins theory of gravity predicts the Moons orbit to within the accuracy of the laser ranging measurements
18.
Reginald Aldworth Daly
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Reginald Aldworth Daly was a Canadian geologist. He was educated at the University of Toronto, where geologist A. P. Coleman persuaded him away from teaching mathematics and he attained his PhD at Harvard, and did postgraduate work in Germany and France. After working as a field geologist for the Canadian International Boundary Commission, he was a professor and he documented the geology alone, but had the help of one field assistant and numerous wranglers and porters. He collected 1,500 rock specimens and made 960 thin sections, the project also included 1,300 photographs, dozens of lake soundings, stratigraphic and structural mapping, petrology, and morphology. In 1912, he filed his report with the Geological Survey of Canada. This work along the 49th parallel led him to formulate a theory of the origins of igneous rocks, according to Dalys biographer, James Natland, Daly was an early proponent of Arthur Holmes and Alfred Wegeners continental drift theory. Daly summarized his ideas in his 1926 book, Our Mobile Earth, Daly applied Newtonian physics to make his point, which was later validated. Daly was awarded the Penrose Medal in 1935, the Wollaston Medal in 1942, in 1950 he became foreign member of the Royal Netherlands Academy of Arts and Sciences. The mineral dalyite and craters on Mars and the Moon are named in his honor and his Cambridge, Massachusetts, house is now a National Historic Landmark. 6, pp. 246–50, Bibcode, 1920PNAS.6. 246D, doi,10. 1073/pnas.6.5.246, PMC1084496, PMID16586806 Daly, R A, Low-Temperature Formation of Alkaline Feldspars in Limestones, Proc. 3, pp. 659–65, Bibcode, 1917PNAS.3. 659D, doi,10. 1073/pnas.3.11.659, PMC1091350, PMID16576265 Daly, R A, A New Test of the Subsidence Theory of Coral Reefs, Proc. Robert M. Hazen, Reginald Aldworth Daly, daly′s Biography, American Geophysical Union James H. Natland, Reginald Aldworth Daly, Eclectic Theoretician of the Earth. 2,2006 Francis Birch, Reginald Aldworth Daly, 1871-1957, A Biographical Memoir National Academy of Sciences, Washington, DC,36 pp.1960 Works by or about Reginald Aldworth Daly at Internet Archive
19.
Harvard University
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Although never formally affiliated with any denomination, the early College primarily trained Congregationalist and Unitarian clergy. Its curriculum and student body were gradually secularized during the 18th century, james Bryant Conant led the university through the Great Depression and World War II and began to reform the curriculum and liberalize admissions after the war. The undergraduate college became coeducational after its 1977 merger with Radcliffe College, Harvards $34.5 billion financial endowment is the largest of any academic institution. Harvard is a large, highly residential research university, the nominal cost of attendance is high, but the Universitys large endowment allows it to offer generous financial aid packages. Harvards alumni include eight U. S. presidents, several heads of state,62 living billionaires,359 Rhodes Scholars. To date, some 130 Nobel laureates,18 Fields Medalists, Harvard was formed in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. In 1638, it obtained British North Americas first known printing press, in 1639 it was named Harvard College after deceased clergyman John Harvard an alumnus of the University of Cambridge who had left the school £779 and his scholars library of some 400 volumes. The charter creating the Harvard Corporation was granted in 1650 and it offered a classic curriculum on the English university model—many leaders in the colony had attended the University of Cambridge—but conformed to the tenets of Puritanism. It was never affiliated with any denomination, but many of its earliest graduates went on to become clergymen in Congregational. The leading Boston divine Increase Mather served as president from 1685 to 1701, in 1708, John Leverett became the first president who was not also a clergyman, which marked a turning of the college toward intellectual independence from Puritanism. When the Hollis Professor of Divinity David Tappan died in 1803 and the president of Harvard Joseph Willard died a year later, in 1804, in 1846, the natural history lectures of Louis Agassiz were acclaimed both in New York and on the campus at Harvard College. Agassizs approach was distinctly idealist and posited Americans participation in the Divine Nature, agassizs perspective on science combined observation with intuition and the assumption that a person can grasp the divine plan in all phenomena. When it came to explaining life-forms, Agassiz resorted to matters of shape based on an archetype for his evidence. Charles W. Eliot, president 1869–1909, eliminated the position of Christianity from the curriculum while opening it to student self-direction. While Eliot was the most crucial figure in the secularization of American higher education, he was motivated not by a desire to secularize education, during the 20th century, Harvards international reputation grew as a burgeoning endowment and prominent professors expanded the universitys scope. Rapid enrollment growth continued as new schools were begun and the undergraduate College expanded. Radcliffe College, established in 1879 as sister school of Harvard College, Harvard became a founding member of the Association of American Universities in 1900. In the early 20th century, the student body was predominately old-stock, high-status Protestants, especially Episcopalians, Congregationalists, by the 1970s it was much more diversified
20.
William Kenneth Hartmann
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William Kenneth Hartmann is a noted planetary scientist, artist, author, and writer. He was the first to convince the scientific mainstream that the Earth had once been hit by a planet sized body, creating both the moon and the Earths 23. 5° tilt. Born in Pennsylvania in 1939, he received his B. S. in physics from Pennsylvania State University, and he is currently a senior scientist at the Planetary Science Institute. He has long been one of Americas leading space artists, and has written and illustrated books on the history of Earth. Hartmann is a Fellow of the International Association of Astronomical Artists and his written work also includes textbooks, short fiction, and novels, the most recent being published in 2002. In 1997 he was the first recipient of the Carl Sagan Medal for Excellence in Public Communication in Planetary Science from the American Astronomical Society, Division for Planetary Sciences. Hartmann was a member of the 1966–1968 University of Colorado UFO Project, asteroid 3341 Hartmann is named after him. Hartmann at the Internet Speculative Fiction Database William Hartmann at the Internet Movie Database William K. Hartmann on Novaspace William Hartmanns Home Page
21.
Donald R. Davis
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Donald R. Davis is an American astronomer specializing in the evolution of the Solar System. With William K. Hartmann, he was responsible for proposing a theory in 1975 of the creation of earths moon by a catastrophic collision and he is credited by the Minor Planet Center with the co-discovery of the trans-Neptunian object 1999 RA215 in 1999. In 2009, he was Academic Director at the Summer Science Program, a few months later, Davis arranged for the naming of an asteroid as 223877 Kutler, after Brendan Kutler -- a student, whom he had worked with in that program -- died in his sleep. The main-belt asteroid 3638 Davis is named in his honor
22.
Protoplanet
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A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitationally perturb each others orbits and collide, in the case of the Solar System, it is thought that the collisions of planetesimals created a few hundred planetary embryos. Such embryos were similar to Ceres and Pluto with masses of about 1022 to 1023 kg and were a few kilometers in diameter. Over the course of hundreds of millions of years, they collided with one another and these in their turn would have collided to create a third generation of fewer but even larger embryos. Eventually, only a handful of embryos were left, which collided to complete the assembly of the planets proper, early protoplanets had more radioactive elements, the quantity of which has been reduced over time due to radioactive decay. Heating due to radioactivity, impact, and gravitational pressure melted parts of protoplanets as they grew toward being planets, in melted zones their heavier elements sank to the center, whereas lighter elements rose to the surface. Such a process is known as planetary differentiation, the composition of some meteorites show that differentiation took place in some asteroids. According to the giant impact hypothesis the Moon formed from an impact of a hypothetical protoplanet called Theia with Earth. In the inner Solar System, the three protoplanets to survive intact are the asteroids Ceres, Pallas, and Vesta. Psyche is likely the survivor of a violent hit-and-run with another object that stripped off the outer, the asteroid Lutetia also has characteristics that resemble a protoplanet. Kuiper-belt dwarf planets have also referred to as protoplanets. In February 2013 astronomers made the first direct observation of a protoplanet forming in a disk of gas, fusor Mesoplanet Planetesimal Thread on the definition of a protoplanet
23.
Greek mythology
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It was a part of the religion in ancient Greece. Greek mythology is explicitly embodied in a collection of narratives. Greek myth attempts to explain the origins of the world, and details the lives and adventures of a variety of gods, goddesses, heroes, heroines. These accounts initially were disseminated in a tradition, today the Greek myths are known primarily from ancient Greek literature. The oldest known Greek literary sources, Homers epic poems Iliad and Odyssey, focus on the Trojan War, archaeological findings provide a principal source of detail about Greek mythology, with gods and heroes featured prominently in the decoration of many artifacts. Geometric designs on pottery of the eighth century BC depict scenes from the Trojan cycle as well as the adventures of Heracles, in the succeeding Archaic, Classical, and Hellenistic periods, Homeric and various other mythological scenes appear, supplementing the existing literary evidence. Greek mythology has had an influence on the culture, arts. Poets and artists from ancient times to the present have derived inspiration from Greek mythology and have discovered contemporary significance and relevance in the themes, Greek mythology is known today primarily from Greek literature and representations on visual media dating from the Geometric period from c. Mythical narration plays an important role in every genre of Greek literature. Nevertheless, the only general mythographical handbook to survive from Greek antiquity was the Library of Pseudo-Apollodorus and this work attempts to reconcile the contradictory tales of the poets and provides a grand summary of traditional Greek mythology and heroic legends. Apollodorus of Athens lived from c, 180–125 BC and wrote on many of these topics. His writings may have formed the basis for the collection, however the Library discusses events that occurred long after his death, among the earliest literary sources are Homers two epic poems, the Iliad and the Odyssey. Other poets completed the cycle, but these later and lesser poems now are lost almost entirely. Despite their traditional name, the Homeric Hymns have no connection with Homer. They are choral hymns from the part of the so-called Lyric age. Hesiods Works and Days, a poem about farming life, also includes the myths of Prometheus, Pandora. The poet gives advice on the best way to succeed in a dangerous world, lyrical poets often took their subjects from myth, but their treatment became gradually less narrative and more allusive. Greek lyric poets, including Pindar, Bacchylides and Simonides, and bucolic poets such as Theocritus and Bion, additionally, myth was central to classical Athenian drama
24.
Titan (mythology)
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In Greek mythology, the Titans and Titanesses were members of the second generation of divine beings, descending from the primordial deities and preceding the Olympian deities. Based on Mount Othrys, the Titans most famously included the first twelve children of the primordial Gaia and they were giant deities of incredible strength, who ruled during the legendary Golden Age, and also comprised the first pantheon of Greek deities. The first twelve Titans comprised the females Mnemosyne, Tethys, Theia, Phoebe, Rhea, and Themis and the males Oceanus, Hyperion, Coeus, Cronus, Crius, like Cronus overthrowing his father Uranus, the Titans were overthrown by Cronus children, in the Titanomachy. The Greeks may have borrowed this mytheme from the Ancient Near East, Greeks of the classical age knew of several poems about the war between the Olympians and Titans. The dominant one, and the one that has survived, was in the Theogony attributed to Hesiod. A lost epic, Titanomachia was mentioned in passing in an essay On Music that was attributed to Plutarch. The Titans also played a prominent role in the poems attributed to Orpheus, although only scraps of the Orphic narratives survive, they show interesting differences with the Hesiodic tradition. Sometimes the elders are supplanted, and sometimes the rebels lose and are either cast out of power entirely or incorporated into the pantheon, the Titanomachy lasted for ten years. The Titans were imprisoned in Tartarus after the war had ended, Tartarus is the deepest spot known in the Underworld, where the most evil beings would be cast into to be tortured for all eternity. Hesiod does not have the last word on the Titans, surviving fragments of poetry ascribed to Orpheus preserve some variations on the myth. In such text, Zeus does not simply set upon his father violently, instead, Rhea spreads out a banquet for Cronus so that he becomes drunk upon fermented honey. Rather than being consigned to Tartarus, Cronus is dragged—still drunk—to the cave of Nyx, another myth concerning the Titans that is not in Hesiod revolves around Dionysus. At some point in his reign, Zeus decides to give up the throne in favor of the infant Dionysus, who like the infant Zeus, is guarded by the Kouretes. The Titans decide to slay the child and claim the throne for themselves, they paint their faces white with gypsum, distract Dionysus with toys, then him and boil. Zeus, enraged, slays the Titans with his thunderbolt, Athena preserves the heart in a gypsum doll and this story is told by the poets Callimachus and Nonnus, who call this Dionysus Zagreus, and in a number of Orphic texts, which do not. Pindar, Plato, and Oppian refer offhandedly to the Titanic nature of humans, according to them, the body is the titanic part, while soul is the divine part of humans. Other early writers imply that humanity was born out of the malevolent blood shed by the Titans in their war against Zeus, Martin Litchfield West also asserts this in relation to shamanistic initiatory rites of early Greek religious practices. Beekes connects the word with τιτώ, burket, Walter, The Orientalizing Revolution, Near Eastern Influence on Greek Culture in the Early Archaic Age, Harvard University Press,1995
25.
Late Heavy Bombardment
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The Late Heavy Bombardment is an event thought to have occurred approximately 4.1 to 3.8 billion years ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. The LHB happened after the Earth and other rocky planets had formed and accreted most of their mass, Evidence for the LHB derives from lunar samples brought back by the Apollo astronauts. Isotopic dating of Moon rocks implies that most impact melts occurred in a narrow interval of time. Several hypotheses attempt to explain the apparent spike in the flux of impactors in the inner Solar System and they also note that the rate of impact cratering could differ significantly between the outer and inner zones of the Solar System. The main piece of evidence for a lunar cataclysm comes from the ages of impact melt rocks that were collected during the Apollo missions. The majority of impact melts are believed to have formed during the collision of asteroids or comets tens of kilometers across. The Apollo 15,16, and 17 landing sites were chosen as a result of their proximity to the Imbrium, Nectaris, under study on Earth, the ages of impact melts collected at these sites clustered between about 3.8 and 4.1 Ga. The apparent clustering of ages of these led to postulation that the record an intense bombardment of the Moon. They called it the lunar cataclysm and proposed that it represented an increase in the rate of bombardment of the Moon around 3.9 Ga. At the time, the conclusion was considered controversial, as more data has become available, particularly from lunar meteorites, this theory, while still controversial, has gained in popularity. The lunar meteorites are believed to randomly sample the lunar surface, many of the feldspathic lunar meteorites probably originated from the lunar far side, and impact melts within these have recently been dated. Consistent with the hypothesis, none of their ages was found to be older than about 3.9 Ga. Nevertheless, the ages do not cluster at this date. Dating of howardite, eucrite and diogenite meteorites and H chondrite meteorites originating from the asteroid belt reveal numerous ages from 3. 4–4.1 Ga, impact velocities above 10 km/s require very high inclinations or the large eccentricities of asteroids on planet crossing orbits. Such objects are rare in the current asteroid belt but the population would be increased by the sweeping of resonances due to giant planet migration. Studies of the highland crater size distributions suggest that the family of projectiles struck Mercury. The first criticism concerns the origin of the impact melt rocks that were sampled at the Apollo landing sites. While these impact melts have been attributed to having been derived from the closest basin. According to this hypothesis, the cluster of impact melt ages near 3.9 Ga simply reflects material being collected from a single impact event, Imbrium
26.
Angle
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In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays lie in a plane, but this plane does not have to be a Euclidean plane, Angles are also formed by the intersection of two planes in Euclidean and other spaces. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection. Similar statements hold in space, for example, the angle formed by two great circles on a sphere is the dihedral angle between the planes determined by the great circles. Angle is also used to designate the measure of an angle or of a rotation and this measure is the ratio of the length of a circular arc to its radius. In the case of an angle, the arc is centered at the vertex. In the case of a rotation, the arc is centered at the center of the rotation and delimited by any other point and its image by the rotation. The word angle comes from the Latin word angulus, meaning corner, cognate words are the Greek ἀγκύλος, meaning crooked, curved, both are connected with the Proto-Indo-European root *ank-, meaning to bend or bow. Euclid defines a plane angle as the inclination to each other, in a plane, according to Proclus an angle must be either a quality or a quantity, or a relationship. In mathematical expressions, it is common to use Greek letters to serve as variables standing for the size of some angle, lower case Roman letters are also used, as are upper case Roman letters in the context of polygons. See the figures in this article for examples, in geometric figures, angles may also be identified by the labels attached to the three points that define them. For example, the angle at vertex A enclosed by the rays AB, sometimes, where there is no risk of confusion, the angle may be referred to simply by its vertex. However, in geometrical situations it is obvious from context that the positive angle less than or equal to 180 degrees is meant. Otherwise, a convention may be adopted so that ∠BAC always refers to the angle from B to C. Angles smaller than an angle are called acute angles. An angle equal to 1/4 turn is called a right angle, two lines that form a right angle are said to be normal, orthogonal, or perpendicular. Angles larger than an angle and smaller than a straight angle are called obtuse angles. An angle equal to 1/2 turn is called a straight angle, Angles larger than a straight angle but less than 1 turn are called reflex angles
27.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
28.
Isotope
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Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
29.
Moon rock
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Moon rock or lunar rock is rock that is found on the Earths moon, or lunar material collected during the course of human exploration of the Moon. During the six Apollo landing missions,2,415 samples weighing 380.96 kilograms were collected, three Luna spacecraft returned with 326 grams of samples. Since 1980, over 120 lunar meteorites representing about 60 different meteorite fall events have been collected on Earth, with a mass of over 48 kilograms. Rocks from the Moon have been measured by radiometric dating techniques and they range in age from about 3.16 billion years old for the basaltic samples derived from the lunar maria, up to about 4.44 billion years old for rocks derived from the highlands. Based on the age dating technique of crater counting, the youngest basaltic eruptions are believed to have occurred about 1.2 billion years ago, in contrast, the oldest ages of rocks from the Earth are between 3.8 and 4.28 billion years old. Almost all lunar rocks are depleted in volatiles and are lacking in hydrated minerals common in Earth rocks. In some regards, lunar rocks are related to Earths rocks in their isotopic composition of the element oxygen. The Apollo moon rocks were collected using a variety of tools, including hammers, rakes, scoops, tongs, most were photographed prior to collection to record the condition in which they were found. They were placed inside sample bags and then a Special Environmental Sample Container for return to the Earth to protect them from contamination, in contrast to the Earth, large portions of the lunar crust appear to be composed of rocks with high concentrations of the mineral anorthite. The mare basalts have relatively high iron values, furthermore, some of the mare basalts have very high levels of titanium. The main repository for the Apollo Moon rocks is the Lunar Sample Laboratory Facility at the Lyndon B. Johnson Space Center in Houston, for safe keeping, there is also a smaller collection stored at White Sands Test Facility in Las Cruces, New Mexico. Most of the rocks are stored in nitrogen to keep free of moisture. They are only handled indirectly, using special tools, Moon rocks collected during the course of lunar exploration are currently considered priceless. In 2002, a safe, containing samples of lunar. The samples were recovered, in 2003, during the court case, naturally transported Moon rocks, although expensive, are widely sold and traded among private collectors. In 1970, US president Richard Nixon gave presentation samples of Moon rock brought back by Apollo 11 as gifts to 135 countries and 50 US states. Composed of many fragments, of sizes, and many shapes, probably from all parts of the Moon, perhaps billions of years old. This rock was later labeled sample 70017, president Nixon ordered the distribution of fragments of the rock to 135 foreign heads of state and the 50 U. S. states
30.
Mantle (geology)
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
31.
Escape velocity
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The escape velocity from Earth is about 11.186 km/s at the surface. More generally, escape velocity is the speed at which the sum of a kinetic energy. With escape velocity in a direction pointing away from the ground of a massive body, once escape velocity is achieved, no further impulse need be applied for it to continue in its escape. When given a speed V greater than the speed v e. In these equations atmospheric friction is not taken into account, escape velocity is only required to send a ballistic object on a trajectory that will allow the object to escape the gravity well of the mass M. The existence of escape velocity is a consequence of conservation of energy, by adding speed to the object it expands the possible places that can be reached until with enough energy they become infinite. For a given gravitational potential energy at a position, the escape velocity is the minimum speed an object without propulsion needs to be able to escape from the gravity. Escape velocity is actually a speed because it does not specify a direction, no matter what the direction of travel is, the simplest way of deriving the formula for escape velocity is to use conservation of energy. Imagine that a spaceship of mass m is at a distance r from the center of mass of the planet and its initial speed is equal to its escape velocity, v e. At its final state, it will be a distance away from the planet. The same result is obtained by a calculation, in which case the variable r represents the radial coordinate or reduced circumference of the Schwarzschild metric. All speeds and velocities measured with respect to the field, additionally, the escape velocity at a point in space is equal to the speed that an object would have if it started at rest from an infinite distance and was pulled by gravity to that point. In common usage, the point is on the surface of a planet or moon. On the surface of the Earth, the velocity is about 11.2 km/s. However, at 9,000 km altitude in space, it is less than 7.1 km/s. The escape velocity is independent of the mass of the escaping object and it does not matter if the mass is 1 kg or 1,000 kg, what differs is the amount of energy required. For an object of mass m the energy required to escape the Earths gravitational field is GMm / r, a related quantity is the specific orbital energy which is essentially the sum of the kinetic and potential energy divided by the mass. An object has reached escape velocity when the orbital energy is greater or equal to zero
32.
Kepler orbit
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In celestial mechanics, a Kepler orbit is the motion of one body relative to another, as an ellipse, parabola, or hyperbola, which forms a two-dimensional orbital plane in three-dimensional space. It is thus said to be a solution of a case of the two-body problem. As a theory in classical mechanics, it also does not take account the effects of general relativity. Keplerian orbits can be parametrized into six orbital elements in various ways, in most applications, there is a large central body, the center of mass of which is assumed to be the center of mass of the entire system. By decomposition, the orbits of two objects of mass can be described as Kepler orbits around their common center of mass. Variations in the motions of the planets were explained by smaller circular paths overlaid on the larger path, as measurements of the planets became increasingly accurate, revisions to the theory were proposed. In 1543, Nicolaus Copernicus published a model of the solar system. In 1601, Johannes Kepler acquired the extensive, meticulous observations of the planets made by Tycho Brahe, Kepler would spend the next five years trying to fit the observations of the planet Mars to various curves. In 1609, Kepler published the first two of his three laws of planetary motion, the first law states, The orbit of every planet is an ellipse with the sun at a focus. More generally, the path of an object undergoing Keplerian motion may also follow a parabola or a hyperbola, alternately, the equation can be expressed as, r = p 1 + e cos Where p is called the semi-latus rectum of the curve. This form of the equation is useful when dealing with parabolic trajectories. Despite developing these laws from observations, Kepler was never able to develop a theory to explain these motions, between 1665 and 1666, Isaac Newton developed several concepts related to motion, gravitation and differential calculus. However, these concepts were not published until 1687 in the Principia, in which he outlined his laws of motion, newtons law of gravitation states, Every point mass attracts every other point mass by a force pointing along the line intersecting both points. The laws of Kepler and Newton formed the basis of modern celestial mechanics until Albert Einstein introduced the concepts of special and general relativity in the early 20th century. For most applications, Keplerian motion approximates the motions of planets and satellites to relatively high degrees of accuracy and is used extensively in astronomy and astrodynamics. See also Orbit Analysis To solve for the motion of an object in a two body system, two simplifying assumptions can be made,1, the bodies are spherically symmetric and can be treated as point masses. There are no external or internal forces acting upon the other than their mutual gravitation. The shapes of large bodies are close to spheres
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Computer simulation
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Computer simulations reproduce the behavior of a system using a model. Simulation of a system is represented as the running of the systems model and it can be used to explore and gain new insights into new technology and to estimate the performance of systems too complex for analytical solutions. The scale of events being simulated by computer simulations has far exceeded anything possible using traditional paper-and-pencil mathematical modeling, other examples include a 1-billion-atom model of material deformation, a 2. Because of the computational cost of simulation, computer experiments are used to perform such as uncertainty quantification. A computer model is the algorithms and equations used to capture the behavior of the system being modeled, by contrast, computer simulation is the actual running of the program that contains these equations or algorithms. Simulation, therefore, is the process of running a model, thus one would not build a simulation, instead, one would build a model, and then either run the model or equivalently run a simulation. It was a simulation of 12 hard spheres using a Monte Carlo algorithm, Computer simulation is often used as an adjunct to, or substitute for, modeling systems for which simple closed form analytic solutions are not possible. The external data requirements of simulations and models vary widely, for some, the input might be just a few numbers, while others might require terabytes of information. Because of this variety, and because diverse simulation systems have common elements. Systems that accept data from external sources must be careful in knowing what they are receiving. While it is easy for computers to read in values from text or binary files, often they are expressed as error bars, a minimum and maximum deviation from the value range within which the true value lie. Even small errors in the data can accumulate into substantial error later in the simulation. While all computer analysis is subject to the GIGO restriction, this is true of digital simulation. Indeed, observation of this inherent, cumulative error in digital systems was the main catalyst for the development of chaos theory, another way of categorizing models is to look at the underlying data structures. For time-stepped simulations, there are two classes, Simulations which store their data in regular grids and require only next-neighbor access are called stencil codes. Many CFD applications belong to this category, if the underlying graph is not a regular grid, the model may belong to the meshfree method class. Equations define the relationships between elements of the system and attempt to find a state in which the system is in equilibrium. Such models are used in simulating physical systems, as a simpler modeling case before dynamic simulation is attempted
34.
Angular momentum
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In physics, angular momentum is the rotational analog of linear momentum. It is an important quantity in physics because it is a conserved quantity – the angular momentum of a system remains constant unless acted on by an external torque. The definition of momentum for a point particle is a pseudovector r×p. This definition can be applied to each point in continua like solids or fluids, unlike momentum, angular momentum does depend on where the origin is chosen, since the particles position is measured from it. The angular momentum of an object can also be connected to the angular velocity ω of the object via the moment of inertia I. However, while ω always points in the direction of the rotation axis, Angular momentum is additive, the total angular momentum of a system is the vector sum of the angular momenta. For continua or fields one uses integration, torque can be defined as the rate of change of angular momentum, analogous to force. Applications include the gyrocompass, control moment gyroscope, inertial systems, reaction wheels, flying discs or Frisbees. In general, conservation does limit the motion of a system. In quantum mechanics, angular momentum is an operator with quantized eigenvalues, Angular momentum is subject to the Heisenberg uncertainty principle, meaning only one component can be measured with definite precision, the other two cannot. Also, the spin of elementary particles does not correspond to literal spinning motion, Angular momentum is a vector quantity that represents the product of a bodys rotational inertia and rotational velocity about a particular axis. Angular momentum can be considered an analog of linear momentum. Thus, where momentum is proportional to mass m and linear speed v, p = m v, angular momentum is proportional to moment of inertia I. Unlike mass, which only on amount of matter, moment of inertia is also dependent on the position of the axis of rotation. Unlike linear speed, which occurs in a line, angular speed occurs about a center of rotation. Therefore, strictly speaking, L should be referred to as the angular momentum relative to that center and this simple analysis can also apply to non-circular motion if only the component of the motion which is perpendicular to the radius vector is considered. In that case, L = r m v ⊥, where v ⊥ = v sin θ is the component of the motion. It is this definition, × to which the moment of momentum refers
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Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
36.
Lagrangian point
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The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centrifugal force required to orbit with them. There are five points, labeled L1 to L5, all in the orbital plane of the two large bodies. The first three are on the line connecting the two bodies, the last two, L4 and L5, each form an equilateral triangle with the two large bodies. The two latter points are stable, which implies that objects can orbit around them in a coordinate system tied to the two large bodies. Several planets have satellites near their L4 and L5 points with respect to the Sun, the three collinear Lagrange points were discovered by Leonhard Euler a few years before Lagrange discovered the remaining two. In 1772, Joseph-Louis Lagrange published an Essay on the three-body problem, in the first chapter he considered the general three-body problem. From that, in the chapter, he demonstrated two special constant-pattern solutions, the collinear and the equilateral, for any three masses, with circular orbits. The five Lagrangian points are labeled and defined as follows, The L1 point lies on the line defined by the two large masses M1 and M2, and between them. It is the most intuitively understood of the Lagrangian points, the one where the attraction of M2 partially cancels M1s gravitational attraction. Explanation An object that orbits the Sun more closely than Earth would normally have an orbital period than Earth. If the object is directly between Earth and the Sun, then Earths gravity counteracts some of the Suns pull on the object, the closer to Earth the object is, the greater this effect is. At the L1 point, the period of the object becomes exactly equal to Earths orbital period. L1 is about 1.5 million kilometers from Earth, the L2 point lies on the line through the two large masses, beyond the smaller of the two. Here, the forces of the two large masses balance the centrifugal effect on a body at L2. Explanation On the opposite side of Earth from the Sun, the period of an object would normally be greater than that of Earth. The extra pull of Earths gravity decreases the orbital period of the object, like L1, L2 is about 1.5 million kilometers from Earth. The L3 point lies on the line defined by the two masses, beyond the larger of the two. Explanation L3 in the Sun–Earth system exists on the side of the Sun
37.
Anorthosite
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Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar, and a minimal mafic component. Pyroxene, ilmenite, magnetite, and olivine are the minerals most commonly present. Anorthosite on Earth can be divided into two types, Proterozoic anorthosite and Archean anorthosite and these two types of anorthosite have different modes of occurrence, appear to be restricted to different periods in Earths history, and are thought to have had different origins. Lunar anorthosites constitute the areas of the Moons surface and have been the subject of much research. Proterozoic anorthosites were emplaced during the Proterozoic Eon, Anorthosite plutons occur in a wide range of sizes. Some smaller plutons, exemplified by many bodies in the U. S. and Harris in Scotland. Larger plutons, like the Mt. Lister Anorthosite, in northern Labrador, Canada, many Proterozoic anorthosites occur in spatial association with other highly distinctive, contemporaneous rock types. These rock types include iron-rich diorite, gabbro, and norite, leucocratic mafic rocks such as leucotroctolite and leuconorite, importantly, large volumes of ultramafic rocks are not found in association with Proterozoic anorthosites. Occurrences of Proterozoic anorthosites are commonly referred to as massifs, however, there is some question as to what name would best describe any occurrence of anorthosite together with the rock types mentioned above. Batholith is used to such occurrences for the remainder of this article. The areal extent of anorthosite batholiths ranges from small to nearly 20,000 km2, in the instance of the Nain Plutonic Suite in northern Labrador. Major occurrences of Proterozoic anorthosite are found in the southwest U. S. the Appalachian Mountains, eastern Canada, across southern Scandinavia and eastern Europe. Mapped onto the Pangaean continental configuration of that eon, these occurrences are all contained in a single straight belt, the conditions and constraints of this pattern of origin and distribution are not clear. However, see the Origins section below, Anorthosites are also common in layered intrusions. Anorthosite in these layered intrusions can form as cumulate layers in the parts of the intrusive complex or as later-stage intrusions into the layered intrusion complex. Since they are composed of plagioclase feldspar, most of Proterozoic anorthosites appear, in outcrop. Individual plagioclase crystals may be black, white, blue, or grey, the feldspar variety labradorite is commonly present in anorthosites. Mineralogically, labradorite is a term for any calcium-rich plagioclase feldspar containing 50–70 molecular percent anorthite
. Bibcode:2016Sci...351..493Y. doi:10.1126/science.aad0525. ISSN 0036-8075. PMID 26823426.
