1.
Elevation
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GIS or geographic information system is a computer system that allows for visualizing, manipulating, capturing, and storage of data with associated attributes. GIS offers better understanding of patterns and relationships of the landscape at different scales, tools inside the GIS allow for manipulation of data for spatial analysis or cartography. A topographical map is the type of map used to depict elevation. In a Geographic Information System, digital models are commonly used to represent the surface of a place. Digital terrain models are another way to represent terrain in GIS, USGS is developing a 3D Elevation Program to keep up with growing needs for high quality topographic data. 3DEP is a collection of enhanced elevation data in the form of high quality LiDAR data over the conterminous United States, Hawaii, there are three bare earth DEM layers in 3DEP which are nationally seamless at the resolution of 1/3,1, and 2 arcseconds. This map is derived from GTOPO30 data that describes the elevation of Earths terrain at intervals of 30 arcseconds and it uses color and shading instead of contour lines to indicate elevation. Hypsography is the study of the distribution of elevations on the surface of the Earth, the term originates from the Greek word ὕψος hypsos meaning height. Most often it is used only in reference to elevation of land, related to the term hypsometry, the measurement of these elevations of a planets solid surface are taken relative to mean datum, except for Earth which is taken relative to the sea level. In the troposphere, temperatures decrease with altitude and this lapse rate is approximately 6.5 °C/km. S
2.
Geodetic datum
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A geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth. An approximate definition of sea level is the datum WGS84, other datums are defined for other areas or at other times, ED50 was defined in 1950 over Europe and differs from WGS84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there. Datums are used in geodesy, navigation, and surveying by cartographers, each starts with an ellipsoid, and then defines latitude, longitude and altitude coordinates. One or more locations on the Earths surface are chosen as anchor base-points, the difference in co-ordinates between datums is commonly referred to as datum shift. The datum shift between two particular datums can vary from one place to another within one country or region, the North Pole, South Pole and Equator will be in different positions on different datums, so True North will be slightly different. Different datums use different interpolations for the shape and size of the Earth. Because the Earth is an ellipsoid, localised datums can give a more accurate representation of the area of coverage than WGS84. OSGB36, for example, is an approximation to the geoid covering the British Isles than the global WGS84 ellipsoid. However, as the benefits of a global system outweigh the greater accuracy, horizontal datums are used for describing a point on the Earths surface, in latitude and longitude or another coordinate system. Vertical datums measure elevations or depths, in surveying and geodesy, a datum is a reference system or an approximation of the Earths surface against which positional measurements are made for computing locations. Horizontal datums are used for describing a point on the Earths surface, vertical datums are used to measure elevations or underwater depths. The horizontal datum is the used to measure positions on the Earth. A specific point on the Earth can have different coordinates. There are hundreds of local horizontal datums around the world, usually referenced to some convenient local reference point, contemporary datums, based on increasingly accurate measurements of the shape of the Earth, are intended to cover larger areas. The WGS84 datum, which is almost identical to the NAD83 datum used in North America, a vertical datum is used as a reference point for elevations of surfaces and features on the Earth including terrain, bathymetry, water levels, and man-made structures. Vertical datums are either, tidal, based on sea levels, gravimetric, based on a geoid, or geodetic, for the purpose of measuring the height of objects on land, the usual datum used is mean sea level. This is a datum which is described as the arithmetic mean of the hourly water elevation taken over a specific 19 years cycle
3.
Geography
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Geography is a field of science devoted to the study of the lands, the features, the inhabitants, and the phenomena of Earth. The first person to use the word γεωγραφία was Eratosthenes, Geography is an all-encompassing discipline that seeks an understanding of the Earth and its human and natural complexities—not merely where objects are, but how they have changed and come to be. It is often defined in terms of the two branches of geography and physical geography. Geography has been called the world discipline and the bridge between the human and the physical sciences, Geography is a systematic study of the Earth and its features. Traditionally, geography has been associated with cartography and place names, although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the space and the temporal database distribution of phenomena, processes, because space and place affect a variety of topics, such as economics, health, climate, plants and animals, geography is highly interdisciplinary. The interdisciplinary nature of the approach depends on an attentiveness to the relationship between physical and human phenomena and its spatial patterns. Names of places. are not geography. know by heart a whole gazetteer full of them would not, in itself and this is a description of the world—that is Geography. In a word Geography is a Science—a thing not of mere names but of argument and reason, of cause, just as all phenomena exist in time and thus have a history, they also exist in space and have a geography. Geography as a discipline can be split broadly into two main fields, human geography and physical geography. The former largely focuses on the environment and how humans create, view, manage. The latter examines the environment, and how organisms, climate, soil, water. The difference between these led to a third field, environmental geography, which combines physical and human geography. Physical geography focuses on geography as an Earth science and it aims to understand the physical problems and the issues of lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns. Physical geography can be divided into broad categories, including, Human geography is a branch of geography that focuses on the study of patterns. It encompasses the human, political, cultural, social, and it requires an understanding of the traditional aspects of physical and human geography, as well as the ways that human societies conceptualize the environment. Integrated geography has emerged as a bridge between the human and the geography, as a result of the increasing specialisation of the two sub-fields. Examples of areas of research in the environmental geography include, emergency management, environmental management, sustainability, geomatics is concerned with the application of computers to the traditional spatial techniques used in cartography and topography
4.
Sea level
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Mean sea level is an average level of the surface of one or more of Earths oceans from which heights such as elevations may be measured. A common and relatively straightforward mean sea-level standard is the midpoint between a low and mean high tide at a particular location. Sea levels can be affected by factors and are known to have varied greatly over geological time scales. The careful measurement of variations in MSL can offer insights into ongoing climate change, the term above sea level generally refers to above mean sea level. Precise determination of a sea level is a difficult problem because of the many factors that affect sea level. Sea level varies quite a lot on several scales of time and this is because the sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point, for example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. One measures the values of MSL in respect to the land, hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates. In the UK, the Ordnance Datum is the sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the datum was MSL at the Victoria Dock, in Hong Kong, mPD is a surveying term meaning metres above Principal Datum and refers to height of 1. 230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and it is used for a part of continental Europe and main part of Africa as official sea level. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001, height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum. It is also used in aviation, where some heights are recorded and reported with respect to sea level, and in the atmospheric sciences. An alternative is to base height measurements on an ellipsoid of the entire Earth, in aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights, however, differences up to 100 metres exist between this ellipsoid height and mean tidal height. The alternative is to use a vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, the elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, for one such case, see Amsterdam Airport Schiphol
5.
Pascal (unit)
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The pascal is the SI derived unit of pressure used to quantify internal pressure, stress, Youngs modulus and ultimate tensile strength. It is defined as one newton per square meter and it is named after the French polymath Blaise Pascal. Common multiple units of the pascal are the hectopascal which is equal to one millibar, the unit of measurement called standard atmosphere is defined as 101,325 Pa and approximates to the average pressure at sea-level at the latitude 45° N. Meteorological reports typically state atmospheric pressure in hectopascals, the unit is named after Blaise Pascal, noted for his contributions to hydrodynamics and hydrostatics, and experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre by the 14th General Conference on Weights, one pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square metre. The unit of measurement called atmosphere or standard atmosphere is 101325 Pa and this value is often used as a reference pressure and specified as such in some national and international standards, such as ISO2787, ISO2533 and ISO5024. In contrast, IUPAC recommends the use of 100 kPa as a standard pressure when reporting the properties of substances, geophysicists use the gigapascal in measuring or calculating tectonic stresses and pressures within the Earth. Medical elastography measures tissue stiffness non-invasively with ultrasound or magnetic resonance imaging, in materials science and engineering, the pascal measures the stiffness, tensile strength and compressive strength of materials. In engineering use, because the pascal represents a small quantity. The pascal is also equivalent to the SI unit of energy density and this applies not only to the thermodynamics of pressurised gases, but also to the energy density of electric, magnetic, and gravitational fields. In measurements of sound pressure, or loudness of sound, one pascal is equal to 94 decibels SPL, the quietest sound a human can hear, known as the threshold of hearing, is 0 dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa, the units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals unit, exceptions include Canada and Portugal, which use kilopascals. In many other fields of science, the SI is preferred, many countries also use the millibar or hectopascal to give aviation altimeter settings. In practically all fields, the kilopascal is used instead. Centimetre of water Metric prefix Orders of magnitude Pascals law
6.
Altimeter
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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, which is related to the term bathymetry, 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, 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 temperature, P is the pressure at altitude z. The constant c depends on the acceleration of gravity and the mass of the air. A barometric altimeter, used along with a map, can help to verify ones location. An altimeter is the most important piece of skydiving equipment, after the parachute itself, altitude awareness is crucial at all times during the jump, and determines the appropriate response to maintain safety. This is the most basic and common type, and is used by all student skydivers. The common design has a face marked from 0 to 4000m, the face plate sports sections prominently marked with yellow and red respectively, signifying the recommended deployment altitude, as well as emergency procedure decision altitude. Some advanced electronic altimeters are also available which use of the familiar analogue display. Digital visual altimeters, mounted on the wrist or hand and this type always operates electronically, and conveys the altitude as a number, rather than a pointer on a dial. An electronic altimeter is turned on on the ground before jump, 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. These are inserted into ones helmet, and emit a warning tone at a predefined altitude, audibles are strictly auxiliary devices, and do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness. Audibles are not recommended and often banned from use by student skydivers and these do not show the precise altitude, but rather help maintain a general indicator in ones peripheral vision. The exact choice of altimeters depends heavily on the individual preferences, experience level, primary disciplines. On one end of the spectrum, a demonstration jump with water landing and no free fall might waive the mandated use of altimeters. Another skydiver doing similar types of jumps might wear a digital altimeter for their primary visual one, in aircraft, an aneroid barometer measures the atmospheric pressure from a static port outside the aircraft
7.
Barometer
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A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather, numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries. Barometers and pressure altimeters are essentially the same instrument, but used for different purposes, the main exception to this is ships at sea, which can use a barometer because their elevation does not change. Due to the presence of weather systems, aircraft altimeters may need to be adjusted as they fly between regions of varying normalized atmospheric pressure. On July 27,1630, Giovanni Battista Baliani wrote a letter to Galileo Galilei explaining an experiment he had made in which a siphon, led over a hill about twenty-one meters high, failed to work. This was a restatement of the theory of horror vacui, which dates to Aristotle, galileos ideas reached Rome in December 1638 in his Discorsi. Raffaele Magiotti and Gasparo Berti were excited by these ideas, Magiotti devised such an experiment, and sometime between 1639 and 1641, Berti carried it out. The bottom end of the tube was opened, and water that had been inside of it poured out into the basin. What was most important about this experiment was that the water had left a space above it in the tube which had no intermediate contact with air to fill it up. This seemed to suggest the possibility of a vacuum existing in the space above the water, Torricelli, a friend and student of Galileo, interpreted the results of the experiments in a novel way. He proposed that the weight of the atmosphere, not a force of the vacuum. It was traditionally thought that the air did not have weight, that is. Even Galileo had accepted the weightlessness of air as a simple truth, Torricelli questioned that assumption, and instead proposed that air had weight and that it was the latter which held up the column of water. He thought that the level the water stayed at was reflective of the force of the airs weight pushing on it. In other words, he viewed the barometer as a balance, an instrument for measurement and he needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced by using mercury, a shorter tube could be used. With mercury, which is about 14 times heavier than water, Pascal further devised an experiment to test the Aristotelian proposition that it was vapors from the liquid that filled the space in a barometer. His experiment compared water with wine, and since the latter was considered more spiritous, Pascal performed the experiment publicly, inviting the Aristotelians to predict the outcome beforehand. The Aristotelians predicted the wine would stand lower, however, Pascal went even further to test the mechanical theory
8.
Atmospheric pressure
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Atmospheric pressure, sometimes also called barometric pressure, is the pressure exerted by the weight of air in the atmosphere of Earth. In most circumstances atmospheric pressure is approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimetre in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilograms and that force is a pressure of 10.1 N/cm2 or 101 kN/m2. A column 1 square inch in cross-section would have a weight of about 14.7 lb or about 65.4 N and it is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The standard atmosphere is a unit of pressure defined as 101325 Pa, the mean sea level pressure is the average atmospheric pressure at sea level. This is the pressure normally given in weather reports on radio, television. When barometers in the home are set to match the weather reports, they measure pressure adjusted to sea level. The altimeter setting in aviation, is an atmospheric pressure adjustment, average sea-level pressure is 1013.25 mbar. In aviation weather reports, QNH is transmitted around the world in millibars or hectopascals, except in the United States, Canada, however, in Canadas public weather reports, sea level pressure is instead reported in kilopascals. The highest sea-level pressure on Earth occurs in Siberia, where the Siberian High often attains a sea-level pressure above 1050 mbar, the lowest measurable sea-level pressure is found at the centers of tropical cyclones and tornadoes, with a record low of 870 mbar. Pressure varies smoothly from the Earths surface to the top of the mesosphere, although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases, one can calculate the atmospheric pressure at a given altitude. Temperature and humidity affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph at right was developed for a temperature of 15 °C, at low altitudes above the sea level, the pressure decreases by about 1.2 kPa for every 100 meters. See pressure system for the effects of air pressure variations on weather, Atmospheric pressure shows a diurnal or semidiurnal cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few millibars and these variations have two superimposed cycles, a circadian cycle and semi-circadian cycle. The highest adjusted-to-sea level barometric pressure recorded on Earth was 1085.7 hPa measured in Tosontsengel
9.
Radar altimeter
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The utilization of radio altimeter equipment is categorised as so-called safety-of-life service, must be protected for Interferences, and is an essential part of Navigation. See also As the name implies, radar is the principle of the system. The system transmits radio waves down to the ground and measures the time it takes them to be reflected back up to the aircraft, the altitude above the ground is calculated from the radio waves travel time and the speed of light. Radar altimeters normally work in the E band, Ka band, or, for more advanced sea-level measurement, radar altimeters also provide a reliable and accurate method of measuring height above water, when flying long sea-tracks. These are critical for use when operating to and from oil rigs, consider a radar pulse emanating from a radar beacon traveling downwards and interacting with a flat ocean surface. The following figure shows an illustration of the vertical cross-section and top-down view of the radar pulse, the radar altimeter measures the return power of the radar pulse thats reflected off the land/ocean surface. The expected return pulse can be derived from a few basic mathematical considerations, alternatively, Frequency Modulated Continuous-wave radar can be used. The greater the frequency shift the further the distance traveled and this method can achieve much better accuracy than the pulsed radar for the same outlay and radar altimeters that use frequency modulation are industry standard. As of 2010, all commercial radar altimeters use linear frequency modulation - continuous wave, as of 2010, about 25,000 aircraft in the US have at least one radio altimeter. That includes all commercial transport and all business aircraft licensed to fly for hire, the top-down view in the figure below shows the decreased footprint size of the delay-doppler signal. First, the footprint is covering less area so the radar pulse emitted by the satellite requires much less power. It covers the radar footprint using more frequent, but less power consuming radar pulses, secondly, the return waveform has a more complex signature allowing the arrival time of the pulse to be more accurately constrained. The following list notes the error associated with radar altimetry measurements. Because tidal periods can be on the order of diurnal and semidiurnal, electromagnetic Bias - There is a sea state bias where the troughs of waves tend to focus waves back to the radar, while the crests of the waves scatter waves away from the radar. Ionosphere - The ionosphere can also impose a delay on the return signal. The electron density in the ionosphere varies throughout the day, complicating the ionosphere correction, wet Troposphere - Water vapor can also cause a delay in the radar signal which can be more difficult to correct. A delay correction for the water column in the radar measurement can be accounted for using output from meteorological models, like ECMWF. In 1924, American engineer Lloyd Espenschied invented the radio altimeter, in 1938, Bell Labs put Espenschieds device in a form that was adaptable for aircraft use
10.
Density altitude
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Density altitude is the altitude relative to the standard atmosphere conditions at which the air density would be equal to the indicated air density at the place of observation. In other words, density altitude is air density given as a height above sea level. Density altitude can also be considered to be the pressure altitude adjusted for non-standard temperature, both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude. In hot and humid conditions, the density altitude at a location may be significantly higher than the true altitude. In aviation, the density altitude is used to assess the aerodynamic performance under certain weather conditions. The lift generated by the aircrafts airfoils and the relation between indicated and true airspeed are also subject to air density changes, furthermore, the power delivered by the aircrafts engine is affected by the air density and air composition. Air density is perhaps the single most important factor affecting aircraft performance and it has a direct bearing on, The lift generated by the wings — reduction in air density reduces the wings lift. The efficiency of the propeller or rotor — which for a propeller behaves similarly to lift on wings, aircraft taking off from a hot and high airport such as the Quito Airport or Mexico City are at a significant aerodynamic disadvantage. The following effects result from a density altitude which is higher than the actual physical altitude, the aircraft will climb slower as the result of reduced power production and lift. Due to these issues, a planes takeoff weight may need to be lowered or takeoffs may need to be scheduled for cooler times of the day. Wind direction and runway slope may need to be taken into account, Density altitude is an important factor in skydiving, and one that can be difficult to judge properly even for experienced skydivers. In addition to the change in wing efficiency common for all aviation. There is a risk due to the high mobility of jumpers. Another factor is the susceptibility to hypoxia at high density altitudes. Density altitude can be calculated from atmospheric pressure and temperature, Density Altitude Calculator Density Altitude influence on aircraft performance Newbyte Atmospheric Calculator, Android Version
11.
International Standard Atmosphere
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The International Standard Atmosphere is an atmospheric model of how the pressure, temperature, density, and viscosity of the Earths atmosphere change over a wide range of altitudes or elevations. It has been established to provide a reference for temperature and pressure and consists of tables of values at various altitudes. The International Organization for Standardization publishes the ISA as an international standard, the ISA mathematical model divides the atmosphere into layers with an assumed linear distribution of absolute temperature T against geopotential altitude h. G is the acceleration of gravity, and Rspecific is the gas constant for dry air. Air density must be calculated in order to solve for the pressure, dynamic viscosity is an empirical function of temperature, and kinematic viscosity is calculated by dividing dynamic viscosity by the density. Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. For example, at sea level the standard gives a pressure of 101,325 pascals, a temperature of 15 °C, a temperature lapse rate of −6.5 °C per km. The tropospheric tabulation continues to 11,000 meters, where the pressure has fallen to 22,632 pascals, the temperature to −56.5 °C, between 11 km and 20 km, the temperature remains constant. Note that the Lapse Rates cited in the table are given as °C per kilometer of geopotential altitude, the ISA model is based on average conditions at mid latitudes, as determined by the ISOs TC 20/SC6 technical committee. It has been revised from time to time since the middle of the 20th century, the ISA models a hypothetical standard day to allow a reproducible engineering reference for calculation and testing of engine and vehicle performance at various altitudes. It does not provide a rigorous model of actual atmospheric conditions. Neither does it account for humidity effects, air is assumed to be dry and clean, the International Civil Aviation Organization published their ICAO Standard Atmosphere as Doc 7488-CD in 1993. It has the model as the ISA, but extends the altitude coverage to 80 kilometers. The ICAO Standard Atmosphere, like the ISA, does not contain water vapor, some of the values defined by ICAO are, Aviation standards and flying rules are based on the International Standard Atmosphere. Airspeed indicators are calibrated on the assumption that they are operating at sea level in the International Standard Atmosphere where the air density is 1.225 kg/m3. Standard Atmosphere is a set of models that define values for temperature, density, pressure. The first model, based on an international standard, was published in 1958 by the U. S. Committee on Extension to the Standard Atmosphere, and was updated in 1962,1966, Standard Atmosphere, International Standard Atmosphere and WMO standard atmospheres are the same as the ISO International Standard Atmosphere for altitudes up to 32 km
12.
Air pressure
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Atmospheric pressure, sometimes also called barometric pressure, is the pressure exerted by the weight of air in the atmosphere of Earth. In most circumstances atmospheric pressure is approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimetre in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kilograms and that force is a pressure of 10.1 N/cm2 or 101 kN/m2. A column 1 square inch in cross-section would have a weight of about 14.7 lb or about 65.4 N and it is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The standard atmosphere is a unit of pressure defined as 101325 Pa, the mean sea level pressure is the average atmospheric pressure at sea level. This is the pressure normally given in weather reports on radio, television. When barometers in the home are set to match the weather reports, they measure pressure adjusted to sea level. The altimeter setting in aviation, is an atmospheric pressure adjustment, average sea-level pressure is 1013.25 mbar. In aviation weather reports, QNH is transmitted around the world in millibars or hectopascals, except in the United States, Canada, however, in Canadas public weather reports, sea level pressure is instead reported in kilopascals. The highest sea-level pressure on Earth occurs in Siberia, where the Siberian High often attains a sea-level pressure above 1050 mbar, the lowest measurable sea-level pressure is found at the centers of tropical cyclones and tornadoes, with a record low of 870 mbar. Pressure varies smoothly from the Earths surface to the top of the mesosphere, although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases, one can calculate the atmospheric pressure at a given altitude. Temperature and humidity affect the atmospheric pressure, and it is necessary to know these to compute an accurate figure. The graph at right was developed for a temperature of 15 °C, at low altitudes above the sea level, the pressure decreases by about 1.2 kPa for every 100 meters. See pressure system for the effects of air pressure variations on weather, Atmospheric pressure shows a diurnal or semidiurnal cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few millibars and these variations have two superimposed cycles, a circadian cycle and semi-circadian cycle. The highest adjusted-to-sea level barometric pressure recorded on Earth was 1085.7 hPa measured in Tosontsengel
13.
Troposphere
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The troposphere is the lowest portion of Earths atmosphere, and is also where nearly all weather takes place. It contains approximately 75% of the mass and 99% of the total mass of water vapor. The average depths of the troposphere are 20 km in the tropics,17 km in the mid latitudes, the lowest part of the troposphere, where friction with the Earths surface influences air flow, is the planetary boundary layer. This layer is typically a few hundred meters to 2 km deep depending on the landform, atop the troposphere is the tropopause, which is the border between the troposphere and stratosphere. The tropopause is a layer, where the air temperature ceases to decrease with height. Most of the phenomena we associate with day-to-day weather occur in the troposphere, by volume, dry air contains 78. 09% nitrogen,20. 95% oxygen,0. 93% argon,0. 04% carbon dioxide, and small amounts of other gases. Air also contains an amount of water vapor. The chemical composition of the troposphere is essentially uniform, with the exception of water vapor. The source of vapor is at the surface through the processes of evaporation. Thus the proportion of water vapor is normally greatest near the surface, the pressure of the atmosphere is maximum at sea level and decreases with altitude. This is because the atmosphere is nearly in hydrostatic equilibrium. The temperature of the troposphere generally decreases as altitude increases, the rate at which the temperature decreases, − d T / d z, is called the environmental lapse rate. The ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The reason for this difference is that the ground absorbs most of the suns energy. Meanwhile, the radiation of heat at the top of the results in the cooling of that part of the atmosphere. The ELR assumes the atmosphere is still, but as air is heated it becomes buoyant, when a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air expands, it pushes the surrounding air outward. As energy transfer to a parcel of air by way of heat is very slow, such a process is called an adiabatic process
14.
Equator
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The Equator usually refers to an imaginary line on the Earths surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. The Equator is about 40,075 kilometres long, some 78. 7% lies across water and 21. 3% over land, other planets and astronomical bodies have equators similarly defined. Generally, an equator is the intersection of the surface of a sphere with the plane that is perpendicular to the spheres axis of rotation. The latitude of the Earths equator is by definition 0° of arc, the equator is the only line of latitude which is also a great circle — that is, one whose plane passes through the center of the globe. The plane of Earths equator when projected outwards to the celestial sphere defines the celestial equator, in the cycle of Earths seasons, the plane of the equator passes through the Sun twice per year, at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over the equator at these times, light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator. Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The Earth bulges slightly at the Equator, the diameter of the Earth is 12,750 kilometres. Because the Earth spins to the east, spacecraft must also launch to the east to take advantage of this Earth-boost of speed, seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earths axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earths position in its orbit, the hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earths axis is not tilted toward the sun, instead it is perpendicular to the sun meaning that the day is about 12 hours long, as is the night, across the whole of the Earth. Near the Equator there is distinction between summer, winter, autumn, or spring. The temperatures are usually high year-round—with the exception of high mountains in South America, the temperature at the Equator can plummet during rainstorms. In many tropical regions people identify two seasons, the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year, the seasons can vary depending on elevation and proximity to an ocean. The Equator lies mostly on the three largest oceans, the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean. The highest point on the Equator is at the elevation of 4,690 metres, at 0°0′0″N 77°59′31″W and this is slightly above the snow line, and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around 1,000 metres lower than on Mount Everest, the Equator traverses the land of 11 countries, it also passes through two island nations, though without making a landfall in either. Starting at the Prime Meridian and heading eastwards, the Equator passes through, Despite its name, however, its island of Annobón is 155 km south of the Equator, and the rest of the country lies to the north
15.
Stratosphere
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The stratosphere is the second major layer of Earths atmosphere, just above the troposphere, and below the mesosphere. About 20% of the mass is contained in the stratosphere. The stratosphere is stratified in temperature, with warmer layers higher and cooler layers closer to the Earth, the increase of temperature with altitude is a result of the absorption of the Suns ultraviolet radiation by the ozone. This is in contrast to the troposphere, near the Earths surface, the border between the troposphere and stratosphere, the tropopause, marks where this temperature inversion begins. Near the equator, the starts at 18 km, at mid latitudes, it starts at 10–13 km and ends at 50 km, at the poles. Temperatures vary within the stratosphere with the seasons, in particular with the polar night, the greatest variation of temperature takes place over the poles in the lower stratosphere, those variations are largely steady at lower latitudes and higher altitudes. The mechanism describing the formation of the layer was described by British mathematician Sydney Chapman in 1930. Molecular oxygen absorbs high energy sunlight in the UV-C region, at shorter than about 240 nm. The oxygen atoms produced combine with oxygen to form ozone. Ozone in turn is photolysed much more rapidly than molecular oxygen as it has an absorption that occurs at longer wavelengths. Ozone photolysis produces O and O2, the oxygen atom product combines with atmospheric molecular oxygen to reform O3, releasing heat. The rapid photolysis and reformation of ozone heats the stratosphere resulting in a temperature inversion and this increase of temperature with altitude is characteristic of the stratosphere, its resistance to vertical mixing means that it is stratified. Within the stratosphere temperatures increase with altitude, the top of the stratosphere has a temperature of about 270 K, overall the attenuation of solar UV at wavelengths that damage DNA by the ozone layer allows life to exist on the surface of the planet outside of the ocean. All air entering the stratosphere must pass through the tropopause, the minimum that divides the troposphere and stratosphere. The rising air is literally freeze dried, the stratosphere is a dry place. The top of the stratosphere is called the stratopause, above which the temperature decreases with height and we now know that there are additional ozone loss mechanisms, and that these mechanisms are catalytic meaning that a small amount of the catalyst can destroy a great number of ozone molecules. The first is due to the reaction of hydroxyl radicals OH· with ozone, OH is formed by the reaction of electronically excited oxygen atoms produced by ozone photolysis, with water vapor. While the stratosphere is dry, additional water vapor is produced in situ by the oxidation of methane
16.
Mesosphere
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The mesosphere is the layer of the Earths atmosphere that is directly above the stratosphere and directly below the mesopause. In the mesosphere, temperature decreases as the altitude increases, the upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring place on Earth with temperatures below −143 °C. The stratosphere, mesosphere and lowest part of the thermosphere are collectively referred to as the middle atmosphere, the mesopause, at an altitude of 80–90 km, separates the mesosphere from the thermosphere—the second-outermost layer of the Earths atmosphere. This is also around the altitude as the turbopause, below which different chemical species are well mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform, the heights of different chemical species differ by their molecular masses. Within the mesosphere, temperature decreases with increasing height, due to decreasing solar heating and increasing cooling by CO2 radiative emission, the top of the mesosphere, called the mesopause, is the coldest part of Earths atmosphere. Temperatures in the mesosphere fall as low as −101 °C, varying according to latitude. The main dynamic features in this region are strong winds, atmospheric tides, internal atmospheric gravity waves. Most of these tides and waves start in the troposphere and lower stratosphere, in the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives global circulation, noctilucent clouds are located in the mesosphere. The upper mesosphere is also the region of the known as the D layer. The D layer is present during the day, when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the mesosphere has been called the ignorosphere because it is poorly studied relative to the stratosphere and the thermosphere. A5 km deep sodium layer is located between 80–105 km, made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the airglow. The sodium has a concentration of 400,000 atoms per cubic centimeter. This band is regularly replenished by sodium sublimating from incoming meteors, astronomers have begun utilizing this sodium band to create guide stars as part of the adaptive optical correction process used to produce ultra-sharp ground-based observations. Millions of meteors enter the Earths atmosphere, averaging 40 tons per year, the mesosphere lies above altitude records for aircraft and balloons, and below the minimum altitude for orbital spacecraft. It has only been accessed through the use of sounding rockets, as a result, it is the least-understood part of the atmosphere
17.
Thermosphere
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The thermosphere is the layer of the Earths atmosphere directly above the mesosphere. The exosphere is above that but is a layer of the atmosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, taking its name from the Greek θερμός meaning heat, the thermosphere begins about 85 kilometres above the Earth. At these high altitudes, the atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation, temperatures are highly dependent on solar activity, and can rise to 2,000 °C. Radiation causes the particles in this layer to become electrically charged, enabling radio waves to be refracted. The highly diluted gas in this layer can reach 2,500 °C during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, a normal thermometer might be significantly below 0 °C, at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above 160 kilometres, the density is so low that molecular interactions are too infrequent to permit the transmission of sound, the dynamics of the thermosphere are dominated by atmospheric tides, which are driven by the very significant diurnal heating. Atmospheric waves dissipate above this level because of collisions between the gas and the ionospheric plasma. The International Space Station orbits the Earth within the middle of the thermosphere and it is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude and at about 85 km. The density of the Earths atmosphere decreases nearly exponentially with altitude, the total mass of the atmosphere is M = ρA H ≃1 kg/cm2 within a column of one square centimeter above the ground. 80% of that mass is concentrated within the troposphere, the mass of the thermosphere above about 85 km is only 0. 002% of the total mass. Therefore, no significant energetic feedback from the thermosphere to the atmospheric regions can be expected. Turbulence causes the air within the atmospheric regions below the turbopause at about 110 km to be a mixture of gases that does not change its composition. Its mean molecular weight is 29 g/mol with molecular oxygen and nitrogen as the two dominant constituents, the lighter constituents atomic oxygen, helium, and hydrogen successively dominate above about 200 km altitude and vary with geographic location, time, and solar activity. The ratio N2/O which is a measure of the density at the ionospheric F region is highly affected by these variations. These changes follow from the diffusion of the constituents through the major gas component during dynamic processes
18.
Exosphere
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In the case of bodies with substantial atmospheres, such as Earths atmosphere, the exosphere is the uppermost layer, where the atmosphere thins out and merges with interplanetary space. It is located directly above the thermosphere, mercury and several large moons, such as the Moon and the Galilean satellites of Jupiter, have exospheres without a denser atmosphere underneath, referred to as a surface boundary exosphere. Here, molecules are ejected on elliptic trajectories until they collide with the surface, smaller bodies such as asteroids, in which the molecules emitted from the surface escape to space, are not considered to have exospheres. The most common molecules within Earths exosphere are those of the lightest atmospheric gasses, hydrogen is present throughout the exosphere, with some helium, carbon dioxide, and atomic oxygen near its base. Because it can be difficult to define the boundary between the exosphere and outer space, the exosphere may be considered a part of interplanetary or outer space, the lower boundary of the exosphere is called the exobase. It is also called exopause and critical altitude as this is the altitude where barometric conditions no longer apply, atmospheric temperature becomes nearly a constant above this altitude. On Earth, the altitude of the ranges from about 500 to 1,000 kilometres depending on solar activity. This is shown in the following, consider a volume of air, with horizontal area A and height equal to the mean free path l, at pressure p and temperature T. For an ideal gas, the number of molecules contained in it is, from the requirement that each molecule traveling upward undergoes on average one collision, the pressure is, p = m A n g A where m A is the mean molecular mass of the gas. Solving these two equations gives, l = R T m A g which is the equation for the scale height. The fluctuation in the height of the exobase is important because this provides atmospheric drag on satellites, in principle, the exosphere covers distances where particles are still gravitationally bound to Earth, i. e. particles still have ballistic orbits that will take them back towards Earth. The upper boundary of the exosphere can be defined as the distance at which the influence of radiation pressure on atomic hydrogen exceeds that of Earths gravitational pull. This happens at half the distance to the Moon, the exosphere, observable from space as the geocorona, is seen to extend to at least 10,000 kilometres from Earths surface. The exosphere is a zone between Earths atmosphere and space. On 17 August 2015, based on studies with the Lunar Atmosphere and Dust Environment Explorer spacecraft, gerd W. Prolss, Physics of the Earths Space Environment, An Introduction
19.
Outer space
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Outer space or just space, is the void that exists between celestial bodies, including Earth. The baseline temperature, as set by the radiation from the Big Bang, is 2.7 kelvins. In most galaxies, observations provide evidence that 90% of the mass is in a form, called dark matter. Data indicates that the majority of the mass-energy in the universe is a poorly understood vacuum energy of space which astronomers label dark energy. Intergalactic space takes up most of the volume of the Universe, there is no firm boundary where outer space starts. However the Kármán line, at an altitude of 100 km above sea level, is used as the start of outer space in space treaties. The framework for international law was established by the Outer Space Treaty. This treaty precludes any claims of sovereignty and permits all states to freely explore outer space. Despite the drafting of UN resolutions for the uses of outer space. Humans began the exploration of space during the 20th century with the advent of high-altitude balloon flights. Earth orbit was first achieved by Yuri Gagarin of the Soviet Union in 1961, due to the high cost of getting into space, manned spaceflight has been limited to low Earth orbit and the Moon. Outer space represents an environment for human exploration because of the dual hazards of vacuum. Microgravity also has an effect on human physiology that causes both muscle atrophy and bone loss. In addition to health and environmental issues, the economic cost of putting objects, including humans. In 350 BCE, Greek philosopher Aristotle suggested that nature abhors a vacuum and this concept built upon a 5th-century BCE ontological argument by the Greek philosopher Parmenides, who denied the possible existence of a void in space. Based on this idea that a vacuum could not exist, in the West it was held for many centuries that space could not be empty. As late as the 17th century, the French philosopher René Descartes argued that the entirety of space must be filled, in ancient China, there were various schools of thought concerning the nature of the heavens, some of which bear a resemblance to the modern understanding. In the 2nd century, astronomer Zhang Heng became convinced that space must be infinite, extending well beyond the mechanism that supported the Sun, the surviving books of the Hsüan Yeh school said that the heavens were boundless, empty and void of substance
20.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
21.
Radiation
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In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles, Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The lower-energy, longer-wavelength part of the spectrum including visible light, infrared light, microwaves and this type of radiation only damages cells if the intensity is high enough to cause excessive heating. Ultraviolet radiation has some features of both ionizing and non-ionizing radiation and these properties derive from ultraviolets power to alter chemical bonds, even without having quite enough energy to ionize atoms. The word radiation arises from the phenomenon of waves radiating from a source and this aspect leads to a system of measurements and physical units that are applicable to all types of radiation. This law does not apply close to a source of radiation or for focused beams. Radiation with sufficiently high energy can ionize atoms, that is to say it can knock electrons off atoms, ionization occurs when an electron is stripped from an electron shell of the atom, which leaves the atom with a net positive charge. Because living cells and, more importantly, the DNA in those cells can be damaged by this ionization, thus ionizing radiation is somewhat artificially separated from particle radiation and electromagnetic radiation, simply due to its great potential for biological damage. While an individual cell is made of trillions of atoms, only a fraction of those will be ionized at low to moderate radiation powers. If the source of the radiation is a radioactive material or a nuclear process such as fission or fusion. Particle radiation is subatomic particles accelerated to relativistic speeds by nuclear reactions, because of their momenta they are quite capable of knocking out electrons and ionizing materials, but since most have an electrical charge, they dont have the penetrating power of ionizing radiation. The exception is neutron particles, see below, there are several different kinds of these particles, but the majority are alpha particles, beta particles, neutrons, and protons. Roughly speaking, photons and particles with energies above about 10 electron volts are ionizing, particle radiation from radioactive material or cosmic rays almost invariably carries enough energy to be ionizing. The radiation is invisible and not directly detectable by human senses, as a result, in some cases, it may lead to secondary emission of visible light upon its interaction with matter, as in the case of Cherenkov radiation and radio-luminescence. Ionizing radiation has many uses in medicine, research and construction. Ultraviolet, of wavelengths from 10 nm to 125 nm, ionizes air molecules, causing it to be absorbed by air
22.
Convection
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Convection is the movement of groups of molecules within fluids such as liquids or gases, and within rheids. Convection takes place through advection, diffusion or both, convection cannot take place in solids because neither bulk current flows nor significant diffusion can take place in solids. Diffusion of heat can take place in solids, but that is called heat conduction, convective heat transfer is one of the major types of heat transfer, and convection is also a major mode of mass transfer in fluids. In the context of heat and mass transfer, the convection is used to refer to the sum of advective and diffusive transfer. In common use the term convection may refer loosely to heat transfer by convection, as opposed to mass transfer by convection, sometimes convection is even used to refer specifically to free heat convection as opposed to forced heat convection. However, in mechanics the correct use of the word is the general sense, convection can be qualified in terms of being natural, forced, gravitational, granular, or thermomagnetic. It may also be said to be due to combustion, capillary action, or Marangoni, heat transfer by natural convection plays a role in the structure of Earths atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be seen as clouds, natural convection also plays a role in stellar physics. The word convection may have different but related usages in different scientific or engineering contexts or applications. The broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause, however, in thermodynamics convection often refers specifically to heat transfer by convection. Additionally, convection includes fluid movement both by bulk motion and by the motion of individual particles, however, in some cases, convection is taken to mean only advective phenomena. Convection occurs on a scale in atmospheres, oceans, planetary mantles. Fluid movement during convection may be slow, or it may be obvious and rapid. On astronomical scales, convection of gas and dust is thought to occur in the disks of black holes. Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion of fluids, heat is the entity of interest being advected, and diffused. Heat is transferred by convection in numerous examples of naturally occurring fluid flow, such as, wind, oceanic currents, convection is also used in engineering practices of homes, industrial processes, cooling of equipment, etc. The rate of heat transfer may be improved by the use of a heat sink. For instance, a typical computer CPU will have a fan to ensure its operating temperature is kept within tolerable limits
23.
Visible spectrum
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The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm, in terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not, however, contain all the colors that the human eyes, unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths. Colors containing only one wavelength are called pure colors or spectral colors. Visible wavelengths pass through the window, the region of the electromagnetic spectrum that allows wavelengths to pass largely unattenuated through the Earths atmosphere. An example of this phenomenon is that clean air scatters blue light more than red wavelengths, the optical window is also referred to as the visible window because it overlaps the human visible response spectrum. The near infrared window lies just out of the vision, as well as the Medium Wavelength IR window. In the 13th century, Roger Bacon theorized that rainbows were produced by a process to the passage of light through glass or crystal. In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light and he was the first to use the word spectrum in this sense in print in 1671 in describing his experiments in optics. The result is red light is bent less sharply than violet as it passes through the prism. Newton divided the spectrum into seven named colors, red, orange, yellow, green, blue, indigo, the human eye is relatively insensitive to indigos frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right. However, the evidence indicates that what Newton meant by indigo, comparing Newtons observation of prismatic colors to a color image of the visible light spectrum shows that indigo corresponds to what is today called blue, whereas blue corresponds to cyan. In the 18th century, Goethe wrote about optical spectra in his Theory of Colours, Goethe used the word spectrum to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors. Goethe argued that the spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow, the spectrum appears only when these edges are close enough to overlap. Young was the first to measure the wavelengths of different colors of light, the connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century
24.
Greenhouse effect
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The greenhouse effect is the process by which radiation from a planets atmosphere warms the planets surface to a temperature above what it would be without its atmosphere. If a planets atmosphere contains radiatively active gases the atmosphere radiate energy in all directions. Part of this radiation is directed towards the surface, warming it, greenhouse gases in the atmosphere radiate energy, some of which is directed to the surface and lower atmosphere. The mechanism that produces this difference between the surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect. Earth’s natural greenhouse effect is critical to supporting life, human activities, primarily the burning of fossil fuels and clearing of forests, have intensified the natural greenhouse effect, causing global warming. The mechanism is named after a faulty analogy with the effect of radiation passing through glass. The way a greenhouse retains heat is fundamentally different, as a works by reducing airflow. The existence of the effect was argued for by Joseph Fourier in 1824. The effect was more fully quantified by Svante Arrhenius in 1896, however, the term greenhouse was not used to refer to this effect by any of these scientists, the term was first used in this way by Nils Gustaf Ekholm in 1901. Earth receives energy from the Sun in the form of ultraviolet, visible, of the total amount of solar energy available at the top of the atmosphere, about 26% is reflected to space by the atmosphere and clouds and 19% is absorbed by the atmosphere and clouds. Most of the energy is absorbed at the surface of Earth. Because the Earths surface is colder than the photosphere of the Sun, most of this thermal radiation is absorbed by the atmosphere, thereby warming it. In addition to the absorption of solar and thermal radiation, the atmosphere gains heat by sensible, the atmosphere radiates energy both upwards and downwards, the part radiated downwards is absorbed by the surface of Earth. This leads to an equilibrium temperature than if the atmosphere were absent. An ideal thermally conductive blackbody at the distance from the Sun as Earth would have a temperature of about 5.3 °C. However, because Earth reflects about 30% of the incoming sunlight, the surface temperature of this hypothetical planet is 33 °C below Earths actual surface temperature of approximately 14 °C. The basic mechanism can be qualified in a number of ways, the atmosphere near the surface is largely opaque to thermal radiation, and most heat loss from the surface is by sensible heat and latent heat transport. Radiative energy losses become increasingly important higher in the atmosphere, largely because of the concentration of water vapor
25.
Adiabatic process
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In thermodynamics, an adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred only as work, the adiabatic process provides a rigorous conceptual basis for the theory used to expound the first law of thermodynamics, and as such it is a key concept in thermodynamics. The adiabatic flame temperature is the temperature that would be achieved by a if the process of combustion took place in the absence of heat loss to the surroundings. A process that does not involve the transfer of heat or matter into or out of a system, so that Q =0, is called an adiabatic process, the assumption that a process is adiabatic is a frequently made simplifying assumption. Even though the cylinders are not insulated and are quite conductive, the same can be said to be true for the expansion process of such a system. The assumption of adiabatic isolation of a system is a useful one, the behaviour of actual machines deviates from these idealizations, but the assumption of such perfect behaviour provide a useful first approximation of how the real world works. According to Laplace, when sound travels in a gas, there is no loss of heat in the medium and the propagation of sound is adiabatic. For this adiabatic process, the modulus of elasticity E = γP where γ is the ratio of specific heats at constant pressure and at constant volume, such a process is called an isentropic process and is said to be reversible. Fictively, if the process is reversed, the energy added as work can be recovered entirely as work done by the system, if the walls of a system are not adiabatic, and energy is transferred in as heat, entropy is transferred into the system with the heat. Such a process is neither adiabatic nor isentropic, having Q >0, naturally occurring adiabatic processes are irreversible. The transfer of energy as work into an isolated system can be imagined as being of two idealized extreme kinds. In one such kind, there is no entropy produced within the system, in nature, this ideal kind occurs only approximately, because it demands an infinitely slow process and no sources of dissipation. The other extreme kind of work is work, for which energy is added as work solely through friction or viscous dissipation within the system. The second law of thermodynamics observes that a process, of transfer of energy as work, always consists at least of isochoric work. Every natural process, adiabatic or not, is irreversible, with ΔS >0, the adiabatic compression of a gas causes a rise in temperature of the gas. Adiabatic expansion against pressure, or a spring, causes a drop in temperature, in contrast, free expansion is an isothermal process for an ideal gas. Adiabatic heating occurs when the pressure of a gas is increased from work done on it by its surroundings and this finds practical application in diesel engines which rely on the lack of quick heat dissipation during their compression stroke to elevate the fuel vapor temperature sufficiently to ignite it. Adiabatic heating occurs in the Earths atmosphere when an air mass descends, for example, in a wind, Foehn wind
26.
Enthalpy of vaporization
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The enthalpy of vaporization is a function of the pressure at which that transformation takes place. The heat of vaporization is temperature-dependent, though a constant heat of vaporization can be assumed for small temperature ranges, the heat of vaporization diminishes with increasing temperature and it vanishes completely at a certain point called the critical temperature. Above the critical temperature, the liquid and vapor phases are indistinguishable, values are usually quoted in J/mol or kJ/mol, although kJ/kg or J/g, and older units like kcal/mol, cal/g and Btu/lb are sometimes still used, among others. The increase in the energy can be viewed as the energy required to overcome the intermolecular interactions in the liquid. Hence helium has a particularly low enthalpy of vaporization,0.0845 kJ/mol, as the van der Waals forces between helium atoms are particularly weak. This is particularly true of metals, which often form covalently bonded molecules in the gas phase, in these cases, the enthalpy of atomization must be used to obtain a true value of the bond energy. An alternative description is to view the enthalpy of condensation as the heat which must be released to the surroundings to compensate for the drop in entropy when a gas condenses to a liquid. These two definitions are equivalent, the point is the temperature at which the increased entropy of the gas phase overcomes the intermolecular forces. Estimation of the enthalpy of vaporization of electrolyte solutions can be carried out using equations based on the chemical thermodynamic models. The vaporization of metals is a key step in metal vapor synthesis, gmelin-Handbuch der anorganischen Chemie /08 a. NIST Chemistry WebBook Young, Francis W. Sears, Mark W. Zemansky, Hugh D
27.
Dew point
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Dew point is the temperature to which air must be cooled to become saturated with water vapor. When further cooled, the water vapor will condense to form liquid dew. Dew point is called frost point when the temperature is below freezing. The measurement of dew point is related to humidity, a higher dew point means there will be more moisture in the air. Given that all the factors influencing humidity remain constant, at ground level the relative humidity rises as the temperature falls. This is because water vapor condenses as the temperature falls. Dew point temperature is never greater than the air temperature because relative humidity cannot exceed 100%. In technical terms, the dew point is the temperature at which the vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At temperatures below the dew point, the rate of condensation will be greater than that of evaporation, the condensed water is called dew when it forms on a solid surface. The condensed water is called either fog or a cloud, depending on its altitude, a high relative humidity implies that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature, when the moisture content remains constant and temperature increases, relative humidity decreases. General aviation pilots use dew point data to calculate the likelihood of carburetor icing and fog, at a given temperature but independent of barometric pressure, the dew point is a consequence of the absolute humidity, the mass of water per unit volume of air. If both the temperature and pressure rise, however, the dew point will increase and the humidity will decrease accordingly. Reducing the absolute humidity without changing other variables will bring the dew point back down to its initial value, in the same way, increasing the absolute humidity after a temperature drop brings the dew point back down to its initial level. If the temperature rises in conditions of constant pressure, then the dew point will remain constant but the relative humidity will drop. For this reason, a constant relative humidity with different temperatures implies that when it is hotter, a higher fraction of the air is present as water vapor compared to when it is cooler. At a given barometric pressure but independent of temperature, the dew point indicates the fraction of water vapor in the air, or, put differently. If the pressure rises without changing this mole fraction, the dew point will rise accordingly, reducing the mole fraction, i. e. making the air less humid, would bring the dew point back down to its initial value
28.
Effects of high altitude on humans
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The effects of high altitude on humans are considerable. The percentage oxygen saturation of hemoglobin determines the content of oxygen in blood, after the human body reaches around 2,100 m above sea level, the saturation of oxyhemoglobin begins to plummet. However, the body has both short-term and long-term adaptations to altitude that allow it to partially compensate for the lack of oxygen. Athletes use these adaptations to help their performance, there is a limit to the level of adaptation, mountaineers refer to the altitudes above 8,000 metres as the death zone, where it is generally believed that no human body can acclimatize. The human body can perform best at sea level, where the pressure is 101,325 Pa or 1013.25 millibars. The concentration of oxygen in air is 20. 9%. In healthy individuals, this saturates hemoglobin, the red pigment in red blood cells. Atmospheric pressure decreases exponentially with altitude while the O2 fraction remains constant to about 100 km, so pO2 decreases exponentially with altitude as well. It is about half of its value at 5,000 m, the altitude of the Everest Base Camp, and only a third at 8,848 m. When pO2 drops, the body responds with altitude acclimatization, the higher the altitude, the greater the risk. Research also indicates elevated risk of permanent brain damage in people climbing to extreme altitudes, expedition doctors commonly stock a supply of dexamethasone, or dex, to treat these conditions on site. Humans have survived for two years at 5,950 m, which is the highest recorded permanently tolerable altitude, at extreme altitudes, above 7,500 m, sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly. The death zone, in mountaineering, refers to altitudes above a point where the amount of oxygen is insufficient to sustain human life. This point is generally tagged as 8,000 m, many deaths in high-altitude mountaineering have been caused by the effects of the death zone, either directly or indirectly. In the death zone, the body cannot acclimatize. An extended stay in the zone without supplementary oxygen will result in deterioration of bodily functions, loss of consciousness, studies have shown that the approximately 140 million people who live at elevations above 2,500 metres have adapted to the lower oxygen levels. These adaptations are especially pronounced in people living in the Andes, compared with acclimatized newcomers, native Andean and Himalayan populations have better oxygenation at birth, enlarged lung volumes throughout life, and a higher capacity for exercise. Tibetans demonstrate an increase in cerebral blood flow, lower hemoglobin concentration
29.
Partial pressure
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In a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture. Gases dissolve, diffuse, and react according to their partial pressures and this general property of gases is also true in chemical reactions of gases in biology. For example, the amount of oxygen for human respiration. This is true across a wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood. Daltons law expresses the fact that the pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases in the mixture. This equality arises from the fact that in a gas the molecules are so far apart that they do not interact with each other. Most actual real-world gases come very close to this ideal. For example, given an ideal gas mixture of nitrogen, hydrogen and ammonia, the partial volume of a particular gas in a mixture is the volume of one component of the gas mixture. It is useful in gas mixtures, e. g. air, to focus on one particular gas component, most often the term is used to describe a liquids tendency to evaporate. It is a measure of the tendency of molecules and atoms to escape from a liquid or a solid, the higher the vapor pressure of a liquid at a given temperature, the lower the normal boiling point of the liquid. The vapor pressure chart displayed has graphs of the vapor pressures versus temperatures for a variety of liquids, as can be seen in the chart, the liquids with the highest vapor pressures have the lowest normal boiling points. For example, at any temperature, methyl chloride 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 of methyl chloride intersects the horizontal pressure line of one atmosphere of absolute vapor pressure. It is possible to work out the equilibrium constant for a reaction involving a mixture of gases given the partial pressure of each gas. However, the reaction kinetics may either oppose or enhance the equilibrium shift, in some cases, the reaction kinetics may be the overriding factor to consider. Gases will dissolve in liquids to an extent that is determined by the equilibrium between the gas and the gas that has dissolved in the liquid. This statement is known as Henrys law and the constant k is quite often referred to as the Henrys law constant
30.
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
31.
Long jump
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The long jump is a track and field event in which athletes combine speed, strength and agility in an attempt to leap as far as possible from a take off point. Along with the jump, the two events that measure jumping for distance as a group are referred to as the horizontal jumps. This event has a history in the Ancient Olympic Games and has been a modern Olympic event for men since the first Olympics in 1896 and for women since 1948. If the competitor starts the leap with any part of the foot past the foul line, a layer of plasticine is placed immediately after the board to detect this occurrence. An official will also watch the jump and make the determination, therefore, it is in the best interest of the competitor to get as close to the foul line as possible. Competitors are allowed to place two marks along the side of the runway in order to assist them to jump accurately. At a lesser meet and facilities, the plasticine will likely not exist, at a smaller meet, the number of attempts might also be limited to four or three. Each competitor has a set number of attempts and that would normally be three trials, with three additional jumps being awarded to the best 8 or 9 competitors. All legal marks will be recorded but only the longest legal jump counts towards the results, the competitor with the longest legal jump at the end of competition is declared the winner. In the event of a tie, then comparing the next best jumps of the tied competitors will be used to determine place. In a large, multi-day elite competition, a set number of competitors will advance to the final round, a set of 3 trial round jumps will be held in order to select those finalists. For record purposes, the maximum accepted wind assistance is two metres per second, the long jump is the only known jumping event of Ancient Greeces original Olympics pentathlon events. All events that occurred at the Olympic Games were initially supposed to act as a form of training for warfare, the long jump emerged probably because it mirrored the crossing of obstacles such as streams and ravines. After investigating the surviving depictions of the ancient event it is believed that unlike the modern event, the athletes carried a weight in each hand, which were called halteres. These weights were swung forward as the athlete jumped in order to increase momentum and it is commonly believed that the jumper would throw the weights behind him in midair to increase his forward momentum, however, halteres were held throughout the duration of the jump. Swinging them down and back at the end of the jump would change the center of gravity and allow the athlete to stretch his legs outward. The jump itself was made from the bater and it was most likely a simple board placed on the stadium track which was removed after the event. The jumpers would land in what was called a skamma, the idea that this was a pit full of sand is wrong
32.
Triple jump
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The triple jump, sometimes referred to as the hop, step and jump or the hop, skip and jump, is a track and field event, similar to the long jump. As a group, the two events are referred to as the horizontal jumps, the competitor runs down the track and performs a hop, a bound and then a jump into the sand pit. The triple jump was inspired by the ancient Olympic Games and has been a modern Olympics event since the Games inception in 1896. The current male and female world record holders are Jonathan Edwards of Great Britain, with a jump of 18.29 m, both records were set during 1995 World Championships in Gothenburg. Historical sources on the ancient Olympic Games occasionally mention jumps of 15 meters or more and this led sports historians to conclude that these must have been a series of jumps, thus providing the basis for the triple jump. The triple jump was a part of the inaugural modern Olympics in Athens, in fact, the first modern Olympic champion, James Connolly, was a triple jumper. Early Olympics also included the standing jump, although this has since been removed from the Olympic program and is rarely performed in competition today. The womens triple jump was introduced into the Atlanta Olympics in 1996, in Irish mythology the geal-ruith, was an event contested in the ancient Irish Tailteann Games as early as 1829 BC. The athlete sprints down a runway to a mark, from which the triple jump is measured. The takeoff mark is commonly a physical piece of wood or similar material embedded in the runway and these boards are placed at different places on the run way depending on how far the athlete can jump. Typically the boards are set, 40ft, 32ft, and 24ft and these are the most common boards you see at the high school and collegiate levels, but boards can be placed anywhere on the runway. There are three phases of the jump, the hop phase, the bound or step phase. These three phases are executed in one continuous sequence, the hop starts with the athlete jumping from the take off board on one leg, which for descriptive purposes will be the right leg. The objective of the first phase is to hop out, focusing all momentum forward, the hop landing phase is very active, involving a powerful backward pawing action of the right leg, with the right take-off foot landing heel first on the runway. This leads to the familiar step-phase mid-air position, with the take off leg trailing flexed at the knee. The step landing forms the beginning of the take-off of the final phase, the jump phase is very similar to the long jump although most athletes have lost too much speed by this time to manage a full hitch kick, and most use a hang or sail technique. When landing in the pit, the jumper should aim to avoid sitting back on landing. The sand pit usually begins 13m from the take off board for international competition, or 11m from the board for international female
33.
Altitude training
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At intermediate altitudes, the air still contains approximately 20. 9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced. Some athletes live permanently at high altitude, only returning to sea level to compete, hypoventilation training, which consists of reducing the breathing frequency while exercising, can also mimic altitude training by significantly decreasing blood and muscle oxygenation. The study of altitude training was heavily delved into during and after the 1968 Olympics and it was during these Olympic Games that endurance events saw significant below-record finishes while anaerobic, sprint events broke all types of records. This was attributed not only to less resistance during movement—due to the less dense air—but also to the nature of the sprint events. Ultimately, these games inspired investigations into altitude training from which unique training principles were developed with the aim of avoiding underperformance, athletes or individuals who wish to gain a competitive edge for endurance events can take advantage of exercising at high altitude. High altitude is defined as any elevation above 1,500 metres. One suggestion for optimizing adaptations and maintaining performance is the live-high, due to the environmental differences at high altitude, it may be necessary to decrease the intensity of workouts. For example, it has shown that athletes performing primarily anaerobic activity do not necessarily benefit from altitude training as they do not rely on oxygen to fuel their performances. A non-training elevation of 2, 100–2,500 metres and training at 1,250 metres or less has shown to be the approach for altitude training. Good venues for live-high train-low include Mammoth Lakes, California, Flagstaff, Arizona, altitude training can produce increases in speed, strength, endurance, and recovery by maintaining altitude exposure for a significant period of time. A study using simulated altitude exposure for 18 days, yet training closer to sea-level, altitude training can produce slow recovery due to the stress of hypoxia. Exposure to extreme hypoxia at altitudes above 16,000 feet can lead to deterioration of skeletal muscle tissue. Five weeks at this leads to a loss of muscle volume of the order of 10–15%. In the live-high, train-high regime, an athlete lives and trains at a desired altitude, the stimulus on the body is constant because the athlete is continuously in a hypoxic environment. Initially VO2 max drops considerably, by around 7% for every 1000 m above sea level) at high altitudes, athletes will no longer be able to metabolize as much oxygen as they would at sea level. Any given velocity must be performed at a higher relative intensity at altitude, however, after long periods of training at altitude, highly trained athletes returning to sea level do not exhibit increased red blood cell count or improved performance on 4000 m cycling tests. In repeated sprints in hypoxia, athletes run short sprints under 30 seconds as fast as they can and they experience incomplete recoveries in hypoxic conditions. The exercise to rest time ratio is less than 1,4, when comparing RSH and repeated sprints in normoxia, studies show that RSH improved time to fatigue and power output
. PMID 9774298.