A magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. Magnetic fields are observed from subatomic particles to galaxies. In everyday life, the effects of magnetic fields are seen in permanent magnets, which pull on magnetic materials and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges such as those used in electromagnets. Magnetic fields exert forces on nearby moving electrical torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field vary with location; as such, it is an example of a vector field. The term'magnetic field' is used for two distinct but related fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter. B, magnetic flux density, is measured in tesla, equivalent to newton per meter per ampere.
H and B differ in. In a vacuum, B and H are the same aside from units. Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated, are both components of the electromagnetic force, one of the four fundamental forces of nature. Magnetic fields are used throughout modern technology in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric generators; the interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect; the Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass. Although magnets and magnetism were studied much earlier, the research of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles.
Noting that the resulting field lines crossed at two points he named those points'poles' in analogy to Earth's poles. He clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them. Three centuries William Gilbert of Colchester replicated Petrus Peregrinus' work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilbert's work, De Magnete, helped to establish magnetism as a science. In 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated. Building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by'magnetic poles' and magnetism is due to small pairs of north/south magnetic poles. Three discoveries in 1820 challenged this foundation of magnetism, though.
Hans Christian Ørsted demonstrated that a current-carrying wire is surrounded by a circular magnetic field. André-Marie Ampère showed that parallel wires with currents attract one another if the currents are in the same direction and repel if they are in opposite directions. Jean-Baptiste Biot and Félix Savart announced empirical results about the forces that a current-carrying long, straight wire exerted on a small magnet, determining that the forces were inversely proportional to the perpendicular distance from the wire to the magnet. Laplace deduced, but did not publish, a law of force based on the differential action of a differential section of the wire, which became known as the Biot–Savart law. Extending these experiments, Ampère published his own successful model of magnetism in 1825. In it, he showed the equivalence of electrical currents to magnets and proposed that magnetism is due to perpetually flowing loops of current instead of the dipoles of magnetic charge in Poisson's model.
This has the additional benefit of explaining. Further, Ampère derived both Ampère's force law describing the force between two currents and Ampère's law, like the Biot–Savart law described the magnetic field generated by a steady current. In this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism. In 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field, he described this phenomenon in. Franz Ernst Neumann proved that, for a moving conductor in a magnetic field, induction is a consequence of Ampère's force law. In the process, he introduced the magnetic vector potential, shown to be equivalent to the underlying mechanism proposed by Faraday. In 1850, Lord Kelvin known as William Thomson, distinguished between two magnetic fields now denoted H and B; the former applied to the latter to Ampère's model and induction. Further, he derived how H and B relate to each other
Argyre Planitia is a plain located within the impact basin Argyre in the southern highlands of Mars. Its name comes from a map produced by Giovanni Schiaparelli in 1877. Argyre is centered at 49.7°S 316.0°E / -49.7. The basin is 1,800 km wide and drops 5.2 km below the surrounding plains. The crater Galle, located on the east rim of Argyre at 51°S 31°W resembles a smiley face; the basin was formed by a giant impact during the Late Heavy Bombardment of the early Solar System 3.9 billion years ago, may be one of the best preserved ancient impact basins from that period. Argyre is surrounded by rugged massifs which form radial patterns around the basin. Several mountain ranges are present, including Nereidum Montes. Four large Noachian epoch channels lie radial to the basin. Three of these channels flowed into Argyre from the south and east through the rim mountains; the fourth, Uzboi Vallis, appears to have flowed out from the basin's north rim to the Chryse region and may have drained a lake of melting ice within the basin.
A smaller outflow channel named Nia Valles is fresh-looking, formed during the early Amazonian after the major fluvial and lacustrine episodes had finished. The original basin floor is buried with friable deflated layered material that may be lake sediment. No inner rings are visible; the impact that formed the Argyre basin struck an ice cap or a thick permafrost layer. Energy from the impact melted the ice and formed a giant lake that sent water to the North; the lakes's volume was equal to that of Earth's Mediterranean Sea. The deepest part of the lake may have taken more than a hundred thousand years to freeze, but with the help of heat from the impact, geothermal heating, dissolved solutes it may have had liquid water for many millions of years; the basin would have supported a regional environment favorable for the origin and the persistence of life. This region shows a great deal of evidence of glacial activity with flow features, crevasse-like fractures, eskers, aretes, horns, U-shaped valleys, terraces.
Because of the shapes of Argyre sinuous ridges, the authors agree with previous publications in that they are eskers. Based on morphometrical and geomorphological analysis of the Argyre eskers and their immediate surroundings, it was suggested that they formed beneath an 2 km thick, stagnant ice sheet around 3.6 billion years ago. This stagnant body of ice might have resembled a Piedmont-style glacier comparable to today's Malaspina Glacier in Alaska. Argyre quadrangle Geography of Mars Lakes on Mars List of plains on Mars Uzboi-Landon-Morava Argyre Planitia map at Google Mars Lakes on Mars - Nathalie Cabrol Media related to Argyre Planitia at Wikimedia Commons
A storm is any disturbed state of an environment or in an astronomical body's atmosphere affecting its surface, implying severe weather. It may be marked by significant disruptions to normal conditions such as strong wind, hail and lightning, heavy precipitation, heavy freezing rain, strong winds, or wind transporting some substance through the atmosphere as in a dust storm, sandstorm, etc. Storms have the potential to harm lives and property via storm surge, heavy rain or snow causing flooding or road impassibility, lightning and vertical wind shear. Systems with significant rainfall and duration help alleviate drought in places. Heavy snowfall can allow special recreational activities to take place which would not be possible otherwise, such as skiing and snowmobiling; the English word comes from Proto-Germanic *sturmaz meaning "noise, tumult". Storms are created when a center of low pressure develops with the system of high pressure surrounding it; this combination of opposing forces can create winds and result in the formation of storm clouds such as cumulonimbus.
Small localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller disturbances such as dust devils and whirlwinds. There are many varieties and names for storms: Blizzard — There are varying definitions for blizzards, both over time and by location. In general, a blizzard is accompanied by gale-force winds, heavy snow, cold conditions; the temperature criterion has fallen out of the definition across the United States Bomb cyclone - A rapid deepening of a mid-latitude cyclonic low-pressure area occurring over the ocean, but can occur over land. The winds experienced during these storms can be as powerful as that of a hurricane. Coastal Storm — large wind waves and/or storm surge that strike the coastal zone, their impacts include coastal erosion and coastal flooding Derecho — A derecho is a widespread, long-lived, straight-line wind storm, associated with a land-based, fast-moving group of severe thunderstorms. Dust devil — a small, localized updraft of rising air.
Dust storm - A situation in which winds pick up large quantities of sand or soil reducing the visibility Firestorm — Firestorms are conflagrations which attain such intensity that they create and sustain their own wind systems. It is most a natural phenomenon, created during some of the largest bushfires, forest fires, wildfires; the Peshtigo Fire is one example of a firestorm. Firestorms can be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden. Nuclear detonations generate firestorms. Gale — An extratropical storm with sustained winds between 34–48 knots. Hailstorm — a type of storm that precipitates round chunks of ice. Hailstorms occur during regular thunderstorms. While most of the hail that precipitates from the clouds is small and harmless, there are occasional occurrences of hail greater than 2 inches in diameter that can cause much damage and injuries. Hypercane -a hypothetical tropical cyclone that could form over 50 °C water; such a storm would produce winds of over 800 km/h.
A series of hypercanes may have formed during the astroid or comet impact that killed the non-avian dinosaurs 66 million years ago. Such a phenomenon could occur during a supervolcanic eruption, or extreme global warming. Ice storm — Ice storms are one of the most dangerous forms of winter storms; when surface temperatures are below freezing, but a thick layer of above-freezing air remains aloft, rain can fall into the freezing layer and freeze upon impact into a glaze of ice. In general, 8 millimetres of accumulation is all, required in combination with breezy conditions, to start downing power lines as well as tree limbs. Ice storms make unheated road surfaces too slick to drive upon. Ice storms can vary in time range from hours to days and can cripple small towns and large metropolitan cities alike. Microburst - a powerful windstorm produced during a thunderstorm that only lasts a few minutes. Ocean Storm or sea storm — Storm conditions out at sea are defined as having sustained winds of 48 knots or greater.
Just referred to as a storm, these systems can sink vessels of all types and sizes. Snowstorm — A heavy fall of snow accumulating at a rate of more than 5 centimeters per hour that lasts several hours. Snow storms ones with a high liquid equivalent and breezy conditions, can down tree limbs, cut off power connections and paralyze travel over large regions. Squall — sudden onset of wind increase of at least 16 knots or greater sustained for at least one minute. Thunderstorm -- A thunderstorm is a type of storm that generates both thunder, it is accompanied by heavy precipitation. Thunderstorms occur throughout the world, with the highest frequency in tropical rainforest regions where there are conditions of high humidity and temperature along with atmospheric instability; these storms occur when high levels of condensation form in a volume of unstable air that generates deep, upward motion in the atmosphere. The heat energy creates powerful rising air currents. Cool descending air currents produce strong downdraughts below the storm.
After the storm has spent its energy, the rising currents die away and downdraughts break up the cloud. Individual s
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, related to the term bathymetry, the measurement of depth under water. Altitude can be determined based on the measurement of atmospheric pressure; the greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft, skydivers use wrist-mounted versions for similar purposes. Hikers and mountain climbers use wrist-mounted or hand-held altimeters, in addition to other navigational tools such as a map, magnetic compass, or GPS receiver; the calibration of an altimeter follows the equation z = c T log , where c is a constant, T is the absolute temperature, P is the pressure at altitude z, Po is the pressure at sea level. The constant c depends on the molar mass of the air.
However, one must be aware that this type of altimeter relies on "density altitude" and its readings can vary by hundreds of feet owing to a sudden change in air pressure, such as from a cold front, without any actual change in altitude. A barometric altimeter, used along with a topographic map, can help to verify one's location, it is more reliable, more accurate, than a GPS receiver for measuring altitude. Because barometric pressure changes with the weather, hikers must periodically re-calibrate their altimeters when they reach a known altitude, such as a trail junction or peak marked on a topographical map. An altimeter is the most important piece of skydiving equipment, after the parachute itself. Altitude awareness is crucial at all times during the jump, determines the appropriate response to maintain safety. Since altitude awareness is so important in skydiving, there is a wide variety of altimeter designs made for use in the sport, a non-student skydiver will use two or more altimeters in a single jump: Hand, wrist or chest-mounted mechanical analogue visual altimeters.
This is the most basic and common type, is used by all student skydivers. The common design has a face marked from 0 to 4000 m, on which an arrow points to the current altitude; the face plate sports sections prominently marked with yellow and red signifying the recommended deployment altitude, as well as emergency procedure decision altitude. A mechanical altimeter has a knob that needs to be manually adjusted to make it point to 0 on the ground before jump, if the landing spot is not at the same altitude as the takeoff spot, the user needs to adjust it appropriately; some advanced electronic altimeters are available which make use of the familiar analogue display, despite internally operating digitally. Digital visual altimeters, mounted on the wrist or hand; this type always operates electronically, conveys the altitude as a number, rather than a pointer on a dial. Since these altimeters contain all the electronic circuitry necessary for altitude calculation, they are equipped with auxiliary functions such as electronic logbook, real-time jump profile replay, speed indication, simulator mode for use in ground training, etc.
An electronic altimeter is activated on the ground before the jump, calibrates automatically to point to 0. It is thus essential that the user not turn it on earlier than necessary to avoid, for example, the drive to a dropzone located at a different altitude than one's home which could cause a fatal false reading. If the intended landing zone is at a different elevation than the takeoff point, the user needs to input the appropriate offset by using a designated function. Audible altimeters; these are inserted into one's helmet, emit a warning tone at a predefined altitude. Contemporary audibles have evolved from their crude beginnings, sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched electronic logbook with data transfer to a PC for analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are auxiliary devices, do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness.
The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves. Auxiliary visual altimeters; these do not show the precise altitude, but rather help maintain a general indicator in one's peripheral vision. They might either operate in tandem with an audible equipped with an appropriate port, in which case they emit warning flashes complementing the audible tones, or be standalone and use another display mode, such as showing either green or red light depending on the altitude. Speaking al
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, is referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance, distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys and polar ice caps of Earth; the days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, 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 and may be a giant impact feature. Mars has two moons and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to 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, less than 1% of the Earth's, except at the lowest elevations for short periods; the two polar ice caps appear to be made of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. In November 2016, NASA reported finding a large amount of underground 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 be seen from Earth with the naked eye, as can its reddish coloring, its apparent magnitude reaches −2.94, surpassed only by Jupiter, the Moon, the Sun.
Optical ground-based telescopes are limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earth's atmosphere. Mars is half the diameter of Earth with a surface area only less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity; the red-orange appearance of the Martian surface is caused by rust. It can look like butterscotch. Like Earth, Mars has differentiated into a dense 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 of iron and nickel with about 16–17% sulfur; this iron sulfide core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, aluminum and potassium.
The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust averages 40 km. Mars is a terrestrial planet that consists of minerals containing silicon and oxygen and other elements that make up rock; the surface of Mars is composed of tholeiitic basalt, although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Localized concentrations of hematite and olivine have been found. Much of the surface is covered by finely grained iron oxide dust. Although Mars has no evidence of a structured global magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.
This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005, is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded, it is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine and sulphur, are much more common on Mars than Earth. After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is underlain by immense impact basins caused by those events.
There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km, or four times the size of the Moon's South Pole – Aitk
Planetary science or, more planetology, is the scientific study of planets and planetary systems and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, formation and history, it is a interdisciplinary field growing from astronomy and earth science, but which now incorporates many disciplines, including planetary geology, atmospheric science, hydrology, theoretical planetary science and exoplanetology. Allied disciplines include space physics, when concerned with the effects of the Sun on the bodies of the Solar System, astrobiology. There are interrelated theoretical branches of planetary science. Observational research can involve a combination of space exploration, predominantly with robotic spacecraft missions using remote sensing, comparative, experimental work in Earth-based laboratories; the theoretical component involves mathematical modelling. Planetary scientists are located in the astronomy and physics or Earth sciences departments of universities or research centres, though there are several purely planetary science institutes worldwide.
There are several major conferences each year, a wide range of peer-reviewed journals. In the case of some exclusive planetary scientists, many of whom are in relation to the study of dark matter, they will seek a private research centre and initiate partnership research tasks; the history of planetary science may be said to have begun with the Ancient Greek philosopher Democritus, reported by Hippolytus as saying The ordered worlds are boundless and differ in size, that in some there is neither sun nor moon, but that in others, both are greater than with us, yet with others more in number. And that the intervals between the ordered worlds are unequal, here more and there less, that some increase, others flourish and others decay, here they come into being and there they are eclipsed, but that they are destroyed by colliding with one another. And that some ordered worlds are bare of animals and plants and all water. In more modern times, planetary science began from studies of the unresolved planets.
In this sense, the original planetary astronomer would be Galileo, who discovered the four largest moons of Jupiter, the mountains on the Moon, first observed the rings of Saturn, all objects of intense study. Galileo's study of the lunar mountains in 1609 began the study of extraterrestrial landscapes: his observation "that the Moon does not possess a smooth and polished surface" suggested that it and other worlds might appear "just like the face of the Earth itself". Advances in telescope construction and instrumental resolution allowed increased identification of the atmospheric and surface details of the planets; the Moon was the most studied, as it always exhibited details on its surface, due to its proximity to the Earth, the technological improvements produced more detailed lunar geological knowledge. In this scientific process, the main instruments were astronomical optical telescopes and robotic exploratory spacecraft; the Solar System has now been well-studied, a good overall understanding of the formation and evolution of this planetary system exists.
However, there are large numbers of unsolved questions, the rate of new discoveries is high due to the large number of interplanetary spacecraft exploring the Solar System. This is both a theoretical science. Observational researchers are predominantly concerned with the study of the small bodies of the Solar System: those that are observed by telescopes, both optical and radio, so that characteristics of these bodies such as shape, surface materials and weathering are determined, the history of their formation and evolution can be understood. Theoretical planetary astronomy is concerned with dynamics: the application of the principles of celestial mechanics to the Solar System and extrasolar planetary systems; the best known research topics of planetary geology deal with the planetary bodies in the near vicinity of the Earth: the Moon, the two neighbouring planets: Venus and Mars. Of these, the Moon was studied first. Geomorphology studies the features on planetary surfaces and reconstructs the history of their formation, inferring the physical processes that acted on the surface.
Planetary geomorphology includes the study of several classes of surface features: Impact features Volcanic and tectonic features Space weathering - erosional effects generated by the harsh environment of space. For example, the thin dust cover on the surface of the lunar regolith is a result of micro meteorite bombardment. Hydrological features: the liquid involved can range from water to hydrocarbon and ammonia, depending on the location within the Solar System; the history of a planetary surface can be deciphered by mapping features from top to bottom according to their deposition sequence, as first determined on terrestrial strata by Nicolas Steno. For example, stratigraphic mapping prepared the Apollo astronauts for the field geology they would encounter on their lunar missions. Overlapping sequences were identified on images taken by the Lunar Orbiter program, these were used to prepare a lunar stratigraphic column and geolog