field_of_work atmosphere of earth
The kelvin is a unit of measure for temperature based upon an absolute scale . It is one of the seven base units in the International System of Units ( SI ) and is assigned the unit symbol K . The Kelvin scale is an absolute , thermodynamic temperature scale using as its null point absolute zero , the temperature at which all thermal motion ceases in the classical description of ___MASK92___ . The kelvin is defined as the fraction of the thermodynamic temperature of the triple point of water ( exactly 0 . 01 ° C or 32 . 018 ° F ). In other words , it is defined such that the triple point of water is exactly 273 . 16 K . The atmosphere of Earth is the layer of gases surrounding the planet Earth that is retained by Earth ' s gravity . The atmosphere protects life on Earth by absorbing ultraviolet solar radiation , warming the surface through heat retention ( greenhouse effect ) , and reducing temperature extremes between day and night ( the diurnal temperature variation ) . The common name air ( ___MASK42___ pronunciation : / r / ) is given to the atmospheric gases used in breathing and photosynthesis . By volume , dry air contains 78 . 09 % nitrogen , 20 . 95 % oxygen , 0 . 93 % argon , 0 . 039 % carbon dioxide , and small amounts of other gases . Air also contains a variable amount of water vapor , on average around 1 % at sea level , and 0 . 4 % over the entire atmosphere . Air content and atmospheric pressure vary at different layers , and air suitable for the survival of terrestrial plants and terrestrial animals is found only in Earth ' s troposphere and artificial atmospheres . The atmosphere has a mass of about 5 . 15 × 1018 kg , three quarters of which is within about 11 km ( 6 . 8 mi ; 36 , 000 ft ) of the surface . The atmosphere becomes thinner and thinner with increasing altitude , with no definite boundary between the atmosphere and outer space . The Kármán line , at 100 km ( 62 mi ) , or 1 . 57 % of Earth ' s radius , is often used as the border between the atmosphere and outer space . Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km ( 75 mi ) . Several layers can be distinguished in the atmosphere , based on characteristics such as temperature and composition . The study of Earth ' s atmosphere and its processes is called atmospheric science ( aerology ) . Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann . Measurement is the assignment of a number to a characteristic of an object or event , which can be compared with other objects or events . The scope and application of a measurement is dependent on the context and discipline . In the natural sciences and ___MASK19___ , measurements do not apply to nominal properties of objects or events , which is consistent with the guidelines of the " International vocabulary of metrology " published by the International Bureau of Weights and Measures . However , in other fields such as ___MASK72___ as well as the social and behavioral sciences , measurements can have multiple levels , which would include nominal , ordinal , interval , and ratio scales . The greenhouse effect is the process by which radiation from a planet ' s atmosphere warms the planet ' s surface to a temperature above what it would be without its atmosphere . X - radiation ( composed of X - rays ) is a form of electromagnetic radiation . Most X - rays have a wavelength ranging from 0 . 01 to 10 nanometers , corresponding to frequencies in the range 30 petahertz to 30 exahertz ( 3 × 10 Hz to 3 × 10 Hz ) and energies in the range 100 eV to 100 keV . X - ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays . In many languages , X - radiation is referred to with terms meaning Röntgen radiation , after the German ( German - Dutch to be precise ) ___MASK52___ Wilhelm Röntgen , who usually is credited as its discoverer , and who had named it " X - radiation " to signify an unknown type of radiation . Spelling of " X - ray ( s )" in the ___MASK42___ language includes the variants " x - ray ( s )", " xray ( s )", and " X ray ( s )". An electric arc or arc discharge is an electrical breakdown of a ___MASK46___ that produces an ongoing electrical discharge . The current through a normally nonconductive medium such as air produces a plasma ; the plasma may produce visible light . An arc discharge is characterized by a lower voltage than a glow discharge , and it relies on thermionic emission of electrons from the electrodes supporting the arc . An archaic term is voltaic arc , as used in the phrase " voltaic arc lamp ". ___MASK27___ ( from , from " phúsis " " ___MASK55___ ") is the natural science that involves the study of matter and its motion and behavior through space and time , along with related concepts such as energy and force . One of the most fundamental scientific disciplines , the main goal of physics is to understand how the universe behaves . Sunset or sundown , is the daily disappearance of the Sun below the horizon as a result of Earth ' s rotation . The Sun will set exactly due west at the equator on the the spring and fall equinoxes , each of which occurs only once a year . The time of sunset is defined in ___MASK4___ as the moment when the trailing edge of the Sun ' s disk disappears below the horizon . Near to the horizon , atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun ' s disk is already about one diameter below the horizon when sunset is observed . A greenhouse ( also called a glasshouse , or , if with sufficient heating , a hothouse ) is a structure with walls and roof made chiefly of transparent material , such as glass , in which plants requiring regulated climatic conditions are grown . These structures range in size from small sheds to industrial - sized buildings . A ___MASK39___ greenhouse is known as a cold frame . The interior of a greenhouse exposed to sunlight becomes significantly warmer than the external ambient temperature , protecting its contents in cold weather . A thermometer is a device that measures temperature or a temperature gradient . A thermometer has two important elements : ( 1 ) a temperature ___MASK16___ ( e . g . the bulb of a mercury - in - glass thermometer ) in which some physical change occurs with temperature , and ( 2 ) some means of converting this physical change into a numerical value ( e . g . the visible scale that is marked on a mercury - in - glass thermometer ). Thermometers are widely used in industry to control and regulate processes , in the study of weather , in ___MASK89___ , and in scientific ___MASK37___ . A temperature is an objective comparative measurement of hot or cold . It is measured by a thermometer . Several scales and units exist for measuring temperature , the most common being Celsius ( denoted ° C ; formerly called " centigrade "), Fahrenheit ( denoted ° F ), and , especially in ___MASK71___ , Kelvin ( denoted K ). A chemical reaction is a process that leads to the transformation of one set of chemical substances to another . Classically , chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms , with no change to the nuclei ( no change to the elements present ), and can often be described by a chemical equation . Nuclear ___MASK73___ is a sub - discipline of ___MASK73___ that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes may occur . In ___MASK81___ , diurnal temperature variation is the variation between a high temperature and a low temperature that occurs during the same day . Life is a characteristic distinguishing physical entities having biological processes , such as signaling and self - sustaining processes , from those that do not , either because such functions have ceased , or because they never had such functions and are classified as inanimate . Various forms of life exist , such as plants , animals , fungi , protists , archaea , and bacteria . The criteria can at times be ambiguous and may or may not define viruses , viroids , or potential artificial life as " living ". ___MASK3___ is the primary science concerned with the study of life , although many other sciences are involved . Ultraviolet ( UV ) is an electromagnetic radiation with a wavelength from 10 nm ( 30 PHz ) to 400 nm ( 750 THz ), shorter than that of visible light but longer than X - rays . UV radiation constitutes about 10 % of the total light output of the Sun , and is thus present in sunlight . It is also produced by electric arcs and specialized lights such as mercury - vapor lamps , tanning lamps , and black lights . Although it is not considered an ionizing radiation because its photons lack the energy to ionize atoms , long - wavelength ultraviolet radiation can cause chemical reactions and causes many substances to glow or fluoresce . Consequently , biological effects of UV are greater than simple heating effects , and many practical applications of UV radiation derive from its interactions with organic molecules . In ___MASK27___ , a wave is an oscillation accompanied by a transfer of energy that travels through a medium ( space or mass ). Frequency refers to the addition of time . " Wave motion " transfers energy from one point to another , which displace particles of the transmission medium  that is , with little or no associated mass transport . Waves consist , instead , of oscillations or vibrations ( of a physical quantity ), around almost fixed locations . In ___MASK27___ , energy is the property that must be transferred to an object in order to perform work on  or to heat  the object , and can be converted in form , but not created or destroyed . The SI unit of energy is the joule , which is the energy transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton . A mercury - vapor lamp is a ___MASK46___ discharge lamp that uses an electric arc through vaporized mercury to produce light . The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb . The outer bulb may be clear or coated with a phosphor ; in either case , the outer bulb provides thermal insulation , protection from the ultraviolet radiation the light produces , and a convenient mounting for the fused quartz arc tube . Fahrenheit is a temperature scale based on one proposed in 1724 by the ___MASK93___ Daniel Gabriel Fahrenheit ( 1686  1736 ), after whom the scale is named . It uses the degree Fahrenheit ( symbol ° F ) as the unit . There exist several accounts of how he originally defined his scale . The lower defining point , 0 ° F , was established as the temperature of a solution of brine made from equal parts of ice and salt . Further limits were established as the melting point of ice ( 32 ° F ) and his best estimate of the average human body temperature ( 96 ° F , about 2 . 6 ° F less than the modern value due to a later redefinition of the scale ). The scale is now usually defined by two fixed points : the temperature at which water freezes into ice is defined as 32 ° F , and the boiling point of water is defined to be 212 ° F , a 180 ° F separation , as defined at sea level and standard atmospheric pressure . In ___MASK27___ , radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium . This includes : The Sun is the star at the center of the Solar System . It is a nearly perfect sphere of hot plasma , with internal convective motion that generates a magnetic field via a dynamo process .< ref name =" doi10 . 1146 / annurev - astro - 081913 - 040012 "></ ref > It is by far the most important source of energy for life on Earth . Its diameter is about 109 times that of Earth , and its mass is about 330 , 000 times that of Earth , ___MASK99___ for about 99 . 86 % of the total mass of the Solar System . About three quarters of the Sun ' s mass consists of hydrogen (~ 73 %); the rest is mostly helium (~ 25 %), with much smaller quantities of heavier elements , including oxygen , carbon , neon , and iron . In ___MASK27___ , heat is that amount of energy flowing from one body to another spontaneously due to their temperature difference , or by any means other than through work or the transfer of matter . The transfer can be by contact between the source and the destination body , as in conduction ; or by radiation between remote bodies ; or by conduction and radiation through a thick solid wall ; or by way of an intermediate fluid body , as in convective circulation ; or by a combination of these . In ___MASK27___ , electromagnetic radiation ( EM radiation or EMR ) refers to the waves ( or their quanta , photons ) of the electromagnetic field , propagating ( radiating ) through space carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , ( visible ) light , ultraviolet , X -, and gamma radiation . In ___MASK27___ , the wavelength of a sinusoidal wave is the spatial period of the wave  the distance over which the wave ' s shape repeats , and thus the inverse of the spatial frequency . It is usually determined by considering the distance between consecutive corresponding points of the same phase , such as crests , troughs , or zero crossings and is a characteristic of both traveling waves and standing waves , as well as other spatial wave patterns . Wavelength is commonly designated by the Greek letter " lambda " (  ). The concept can also be applied to periodic waves of non - sinusoidal shape . The term " wavelength " is also sometimes applied to modulated waves , and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids . Earth , otherwise known as the world , 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 . Night or nighttime (" sp ." night - time or night time ) is the period of time between the sunset and the sunrise when the Sun is below the horizon . Celsius , also known as centigrade , is a scale and unit of measurement for temperature . As an SI derived unit , it is used by most countries in the world . It is named after the Swedish ___MASK25___ Anders Celsius ( 1701  1744 ), who developed a similar temperature scale . The degree Celsius (° C ) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval , a difference between two temperatures or an uncertainty . Before being renamed to honour Anders Celsius in 1948 , the unit was called " centigrade ", from the Latin " centum ", which means 100 , and " gradus ", which means steps . ___MASK81___ is the interdisciplinary scientific study of the atmosphere . The study of ___MASK81___ dates back millennia , though significant progress in ___MASK81___ did not occur until the 18th century . The 19th century saw modest progress in the field after weather observation networks were formed across broad regions . Prior attempts at prediction of weather depended on historical data . It wasn ' t until after the elucidation of the laws of physics and , more particularly , the development of the computer , allowing for the automated solution of a great many equations that model the weather , in the latter half of the 20th century that significant breakthroughs in weather forecasting were achieved .