In physics, special relativity is the accepted and experimentally well-confirmed physical theory regarding the relationship between space and time. In Albert Einstein's original pedagogical treatment, it is based on two postulates: the laws of physics are invariant in all inertial systems. Special relativity was proposed by Albert Einstein in a paper published 26 September 1905 titled "On the Electrodynamics of Moving Bodies"; the inconsistency of Newtonian mechanics with Maxwell's equations of electromagnetism and the lack of experimental confirmation for a hypothesized luminiferous aether led to the development of special relativity, which corrects mechanics to handle situations involving all motions and those at a significant fraction of the speed of light. Today, special relativity is the most accurate model of motion at any speed when gravitational effects are negligible. So, the Newtonian mechanics model is still valid as a simple and high accuracy approximation at low velocities relative to the speed of light.
Special relativity implies a wide range of consequences, which have been experimentally verified, including length contraction, time dilation, relativistic mass, mass–energy equivalence, a universal speed limit, the speed of causality and relativity of simultaneity. It has replaced the conventional notion of an absolute universal time with the notion of a time, dependent on reference frame and spatial position. Rather than an invariant time interval between two events, there is an invariant spacetime interval. Combined with other laws of physics, the two postulates of special relativity predict the equivalence of mass and energy, as expressed in the mass–energy equivalence formula E = mc2, where c is the speed of light in a vacuum. A defining feature of special relativity is the replacement of the Galilean transformations of Newtonian mechanics with the Lorentz transformations. Time and space cannot be defined separately from each other. Rather and time are interwoven into a single continuum known as "spacetime".
Events that occur at the same time for one observer can occur at different times for another. Not until Einstein developed general relativity, introducing a curved spacetime to incorporate gravity, was the phrase "special relativity" employed. A translation, used is "restricted relativity"; the theory is "special" in that it only applies in the special case where the spacetime is flat, i.e. the curvature of spacetime, described by the energy-momentum tensor and causing gravity, is negligible. In order to accommodate gravity, Einstein formulated general relativity in 1915. Special relativity, contrary to some outdated descriptions, is capable of handling accelerations as well as accelerated frames of reference; as Galilean relativity is now accepted to be an approximation of special relativity, valid for low speeds, special relativity is considered an approximation of general relativity, valid for weak gravitational fields, i.e. at a sufficiently small scale and in conditions of free fall. Whereas general relativity incorporates noneuclidean geometry in order to represent gravitational effects as the geometric curvature of spacetime, special relativity is restricted to the flat spacetime known as Minkowski space.
As long as the universe can be modeled as a pseudo-Riemannian manifold, a Lorentz-invariant frame that abides by special relativity can be defined for a sufficiently small neighborhood of each point in this curved spacetime. Galileo Galilei had postulated that there is no absolute and well-defined state of rest, a principle now called Galileo's principle of relativity. Einstein extended this principle so that it accounted for the constant speed of light, a phenomenon, observed in the Michelson–Morley experiment, he postulated that it holds for all the laws of physics, including both the laws of mechanics and of electrodynamics. Einstein discerned two fundamental propositions that seemed to be the most assured, regardless of the exact validity of the known laws of either mechanics or electrodynamics; these propositions were the constancy of the speed of light in a vacuum and the independence of physical laws from the choice of inertial system. In his initial presentation of special relativity in 1905 he expressed these postulates as: The Principle of Relativity – the laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems in uniform translatory motion relative to each other.
The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity c, independent of the state of motion of the emitting body". That is, light in vacuum propagates with the speed c in at least one system of inertial coordinates, regardless of the state of motion of the light source; the constancy of the speed of light was motivated by Maxwell's theory of electromagnetism and the lack of evidence for the luminiferous ether. There is conflicting evidence on the extent to which Einstein was influenced by the null result of the Michelson–Morley experiment. In any case, the null result of the Michelson–Morley experiment helped the notion of the constancy of the speed of light gain widespread and rapid acce
A corona is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most seen during a total solar eclipse, but it is observable with a coronagraph; the word corona is a Latin word meaning "crown", from the Ancient Greek κορώνη. Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1,000,000 kelvins, much hotter than the surface of the Sun. Light from the corona comes from the same volume of space; the K-corona is created by sunlight scattering off free electrons. The F-corona is created by sunlight bouncing off dust particles, is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the E-corona is due to spectral emission lines produced by ions that are present in the coronal plasma. In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that the aura visible during a solar eclipse belongs to the Sun not to the Moon.
In 1809, Spanish astronomer José Joaquín de Ferrer coined the term'corona'. Based in his own observations of the 1806 solar eclipse at Kinderhook, de Ferrer proposed that the corona was part of the Sun and not of the Moon. English astronomer Norman Lockyer identified the first element unknown on Earth in the Sun's chromosphere, called helium. French astronomer Jules Jenssen noted that the size and shape of the corona changes with the sunspot cycle. In 1930, Bernard Lyot invented the coronograph, which allows to see the corona without a total eclipse. In 1952, American astronomer Eugene Parker proposed that the solar corona might be heated by myriad tiny'nanoflares', miniature brightenings resembling solar flares that would occur all over the surface of the Sun; the high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a unknown element, "coronium". Instead, these spectral features have since been explained by ionized iron.
Bengt Edlén, following the work of Grotrian, first identified the coronal spectral lines in 1940 as transitions from low-lying metastable levels of the ground configuration of ionised metals. The sun's corona is much hotter than the visible surface of the Sun: the photosphere's average temperature is 5800 kelvins compared to the corona's one to three million kelvins; the corona is 10−12 times as dense as the photosphere, so produces about one-millionth as much visible light. The corona is separated from the photosphere by the shallow chromosphere; the exact mechanism by which the corona is heated is still the subject of some debate, but possibilities include induction by the Sun's magnetic field and magnetohydrodynamic waves from below. The outer edges of the Sun's corona are being transported away due to open magnetic flux and hence generating the solar wind; the corona is not always evenly distributed across the surface of the sun. During periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions.
However, during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity. The solar cycle spans 11 years, from solar minimum to the following minimum. Since the solar magnetic field is continually wound up due to the faster rotation of mass at the sun's equator, sunspot activity will be more pronounced at solar maximum where the magnetic field is more twisted. Associated with sunspots are coronal loops, loops of magnetic flux, upwelling from the solar interior; the magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the dark sun spots. Since the corona has been photographed at high resolution in the X-ray range of the spectrum by the satellite Skylab in 1973, later by Yohkoh and the other following space instruments, it has been seen that the structure of the corona is quite varied and complex: different zones have been classified on the coronal disc.
The astronomers distinguish several regions, as described below. Active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops, they distribute in two zones of activity, which are parallel to the solar equator. The average temperature is between two and four million kelvins, while the density goes from 109 to 1010 particle per cm3. Active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights above the Sun's surface: sunspots and faculae, occur in the photosphere, spicules, Hα filaments and plages in the chromosphere, prominences in the chromosphere and transition region, flares and coronal mass ejections happen in the corona and chromosphere. If flares are violent, they can perturb the photosphere and generate a Moreton wave. On the contrary, quiescent prom
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word refers to visible light, the visible spectrum, visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared and the ultraviolet. This wavelength means a frequency range of 430–750 terahertz; the main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars in the form of starches, which release energy into the living things that digest them; this process of photosynthesis provides all the energy used by living things. Another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has replaced firelight; some species of animals generate their own light, a process called bioluminescence.
For example, fireflies use light to locate mates, vampire squids use it to hide themselves from prey. The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays and radio waves are light. Like all types of EM radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed; the absorbed energy of the EM waves is called a photon, represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave collapses to a single location, this location is where the photon "arrives."
This is. This dual wave-like and particle-like nature of light is known as the wave–particle duality; the study of light, known as optics, is an important research area in modern physics. EM radiation, or EMR, is classified by wavelength into radio waves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays, gamma rays; the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, lower frequencies have longer wavelengths; when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. EMR in the visible light region consists of quanta that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule. At the lower end of the visible light spectrum, EMR becomes invisible to humans because its photons no longer have enough individual energy to cause a lasting molecular change in the visual molecule retinal in the human retina, which change triggers the sensation of vision.
There exist animals that are sensitive to various types of infrared, but not by means of quantum-absorption. Infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, how these animals detect it. Above the range of visible light, ultraviolet light becomes invisible to humans because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. Various sources define visible light as narrowly as 420–680 nm to as broadly as 380–800 nm. Under ideal laboratory conditions, people can see infrared up to at least 1050 nm.
Plant growth is affected by the color spectrum of light, a process known as photomorphogenesis. The speed of light in a vacuum is defined to be 299,792,458 m/s; the fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at this same speed in vacuum. Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. An early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Rømer observed one of its moons, Io. Noting discrepancies in the apparent period of Io's orbit, he calculated that light takes about 22 minutes to traverse the diameter of Earth's orbit. However, its size was not known at that time. If Rømer had known the diameter of the Earth's orbit, he would have calculated a speed of 227,000,000 m/s. Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849.
A SQUID is a sensitive magnetometer used to measure subtle magnetic fields, based on superconducting loops containing Josephson junctions. SQUIDs are sensitive enough to measure fields as low as 5 aT with a few days of averaged measurements, their noise levels are as low as 3 fT·Hz−½. For comparison, a typical refrigerator magnet produces 0.01 tesla, some processes in animals produce small magnetic fields between 10−9 T and 10−6 T. Invented SERF atomic magnetometers are more sensitive and do not require cryogenic refrigeration but are orders of magnitude larger in size and must be operated in a near-zero magnetic field. There are two main types of SQUID: direct radio frequency. RF SQUIDs can work with only one Josephson junction, which might make them cheaper to produce, but are less sensitive; the DC SQUID was invented in 1964 by Robert Jaklevic, John J. Lambe, James Mercereau, Arnold Silver of Ford Research Labs after Brian David Josephson postulated the Josephson effect in 1962, the first Josephson junction was made by John Rowell and Philip Anderson at Bell Labs in 1963.
It has two Josephson junctions in parallel in a superconducting loop. It is based on the DC Josephson effect. In the absence of any external magnetic field, the input current I splits into the two branches equally. If a small external magnetic field is applied to the superconducting loop, a screening current, I s, begins circulating in the loop that generates a magnetic field canceling the applied external flux; the induced current is in the same direction as I in one of the branches of the superconducting loop, is opposite to I in the other branch. As soon as the current in either branch exceeds the critical current, I c, of the Josephson junction, a voltage appears across the junction. Now suppose the external flux is further increased until it exceeds Φ 0 / 2, half the magnetic flux quantum. Since the flux enclosed by the superconducting loop must be an integer number of flux quanta, instead of screening the flux the SQUID now energetically prefers to increase it to Φ 0; the current now flows in the opposite direction, opposing the difference between the admitted flux Φ 0 and the external field of just over Φ 0 / 2.
The current decreases as the external field is increased, is zero when the flux is Φ 0, again reverses direction as the external field is further increased. Thus, the current changes direction periodically, every time the flux increases by additional half-integer multiple of Φ 0, with a change at maximum amperage every half-plus-integer multiple of Φ 0 and at zero amps every integer multiple. If the input current is more than I c the SQUID always operates in the resistive mode; the voltage, in this case, is thus a function of the applied magnetic field and the period equal to Φ 0. Since the current-voltage characteristic of the DC SQUID is hysteretic, a shunt resistance, R is connected across the junction to eliminate the hysteresis; the screening current is the applied flux divided by the self-inductance of the ring. Thus Δ Φ can be estimated as the function of Δ V as follows: Δ V = R ⋅ Δ I 2 ⋅ I = 2 ⋅ Δ Φ L, where L is the self inductance of the superconducting ring Δ V = R L ⋅ Δ Φ The discussion in this Section assumed perfect flux quantization in the loop.
However, this is only true for big loops with a large self-inductance. According to the relations, given above, this implies small current and voltage variations. In practice the self-inductance L of the loop is not so large; the general case can be evaluated by introducing a parameter λ = i c L Φ 0 with i c the critical current of the SQUID. Λ is of order one. The RF SQUID was invented in 1965 by Robert Jaklevic, John J. Lambe, Arnold Silver, James Edwar
A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole; the boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways, a black hole acts like an ideal black body. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass; this temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it impossible to observe. Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.
The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; the discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. Black holes of stellar mass are expected to form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus. Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light.
Matter that falls onto a black hole can form an external accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location; such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses. On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves, which represented the first observation of a black hole merger; as of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope in 2017 of the supermassive black hole in Messier 87's galactic centre.
Larry Kimura, a Hawaiian language professor at the University of Hawaii at Hilo, named the hole Pōwehi—a Hawaiian phrase referring to an "embellished dark source of unending creation." The idea of a body so massive that light could not escape was proposed by astronomical pioneer and English clergyman John Michell in a letter published in November 1784. Michell's simplistic calculations assumed that such a body might have the same density as the Sun, concluded that such a body would form when a star's diameter exceeds the Sun's by a factor of 500, the surface escape velocity exceeds the usual speed of light. Michell noted that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies. Scholars of the time were excited by the proposal that giant but invisible stars might be hiding in plain view, but enthusiasm dampened when the wavelike nature of light became apparent in the early nineteenth century. If light were a wave rather than a "corpuscle", it became unclear what, if any, influence gravity would have on escaping light waves.
Modern relativity discredits Michell's notion of a light ray shooting directly from the surface of a supermassive star, being slowed down by the star's gravity and free-falling back to the star's surface. In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties; this solution had a peculiar behaviour at what is now called the Schwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time. In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates, although it took until 1933 for Georges Lemaître to realize that this meant the singularity at the Schwarzschild radius was a non-physical coordinate singularity.
Arthur Eddington did however comment on the possibility of a star with mass c
Washington University in St. Louis
Washington University in St. Louis is a private research university in St. Louis, Missouri. Founded in 1853, named after George Washington, the university has students and faculty from all 50 U. S. states and more than 120 countries. As of 2017, 24 Nobel laureates in economics and medicine, physics have been affiliated with Washington University, nine having done the major part of their pioneering research at the university. Washington University's undergraduate program is ranked 19th by U. S. News & World Report in 2018 and 11th by The Wall Street Journal in their 2018 rankings; the university is ranked 20th in the world in 2018 by the Academic Ranking of World Universities. The acceptance rate for the class of 2023 was 14%, with students selected from more than 31,000 applications. Of students admitted 90 percent were in the top 10 percent of their class. Washington University is made up of seven graduate and undergraduate schools that encompass a broad range of academic fields. To prevent confusion over its location, the Board of Trustees added the phrase "in St. Louis" in 1976.
Washington University was conceived by 17 St. Louis business and religious leaders concerned by the lack of institutions of higher learning in the Midwest. Missouri State Senator Wayman Crow and Unitarian minister William Greenleaf Eliot, grandfather of the poet T. S. Eliot, led the effort; the university's first chancellor was Joseph Gibson Hoyt. Crow secured the university charter from the Missouri General Assembly in 1853, Eliot was named President of the Board of Trustees. Early on, Eliot solicited support from members of the local business community, including John O'Fallon, but Eliot failed to secure a permanent endowment. Washington University is unusual among major American universities in not having had a prior financial endowment; the institution had no backing of a religious organization, single wealthy patron, or earmarked government support. During the three years following its inception, the university bore three different names; the board first approved "Eliot Seminary," but William Eliot was uncomfortable with naming a university after himself and objected to the establishment of a seminary, which would implicitly be charged with teaching a religious faith.
He favored a nonsectarian university. In 1854, the Board of Trustees changed the name to "Washington Institute" in honor of George Washington. Naming the University after the nation's first president, only seven years before the American Civil War and during a time of bitter national division, was no coincidence. During this time of conflict, Americans universally admired George Washington as the father of the United States and a symbol of national unity; the Board of Trustees believed that the university should be a force of unity in a divided Missouri. In 1856, the University amended its name to "Washington University." The university amended its name once more in 1976, when the Board of Trustees voted to add the suffix "in St. Louis" to distinguish the university from the nearly two dozen other universities bearing Washington's name. Although chartered as a university, for many years Washington University functioned as a night school located on 17th Street and Washington Avenue in the heart of downtown St. Louis.
Owing to limited financial resources, Washington University used public buildings. Classes began on October 1854, at the Benton School building. At first the university paid for the evening classes, but as their popularity grew, their funding was transferred to the St. Louis Public Schools; the board secured funds for the construction of Academic Hall and a half dozen other buildings. The university divided into three departments: the Manual Training School, Smith Academy, the Mary Institute. In 1867, the university opened the first private nonsectarian law school west of the Mississippi River. By 1882, Washington University had expanded to numerous departments, which were housed in various buildings across St. Louis. Medical classes were first held at Washington University in 1891 after the St. Louis Medical College decided to affiliate with the University, establishing the School of Medicine. During the 1890s, Robert Sommers Brookings, the president of the Board of Trustees, undertook the tasks of reorganizing the university's finances, putting them onto a sound foundation, buying land for a new campus.
Washington University spent its first half century in downtown St. Louis bounded by Washington Ave. Lucas Place, Locust Street. By the 1890s, owing to the dramatic expansion of the Manual School and a new benefactor in Robert Brookings, the University began to move west; the University board of directors began a process to find suitable ground and hired the landscape architecture firm Olmsted, Olmsted & Eliot of Boston. A committee of Robert S. Brookings, Henry Ware Eliot, William Huse found a site of 103 acres just beyond Forest Park, located west of the city limits in St. Louis County; the elevation of the land was thought to resemble the Acropolis and inspired the nickname of "Hilltop" campus, renamed the Danforth campus in 2006 to honor former chancellor William H. Danforth. In 1899, the university opened a national design contest for the new campus; the renowned Philadelphia firm Cope & Stewardson won unanimously with its plan for a row of Collegiate Gothic quadrangles inspired by Oxford and Cambridge Universities.
The cornerstone of the first building, Busch Hall, was laid on October 20, 1900. The construction of Brookings Hall and Cupples began shortly thereafter; the school delayed occupying these buildings until 1905 to accommodate the 1904 World's Fair and Olympics. The delay allowed the university to construct ten buildings instead of t
Outline of astronomy
The following outline is provided as an overview of and topical guide to astronomy: Astronomy – studies the universe beyond Earth, including its formation and development, the evolution, chemistry and motion of celestial objects and phenomena that originate outside the atmosphere of Earth. Astronomy can be described as all the following: An academic discipline: one with academic departments and degrees. A scientific field – recognized category of specialized expertise within science, embodies it A natural science – one that seeks to elucidate the rules that govern the natural world using empirical and scientific methods. A branch or field of space science A hobby or part-time pursuit for the satisfaction of personal curiosity or appreciation of beauty, the latter including astrophotography. Astrobiology – studies the advent and evolution of biological systems in the universe. Astrophysics – branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior.
Among the objects studied are galaxies, planets, the interstellar medium and the cosmic microwave background. The subdisciplines of theoretical astrophysics are: Compact objects – this subdiscipline studies dense matter in white dwarfs and neutron stars and their effects on environments including accretion. Physical cosmology – origin and evolution of the universe as a whole; the study of cosmology is theoretical astrophysics at its largest scale. Computational astrophysics – The study of astrophysics using computational methods and tools to develop computational models. Galactic astronomy – deals with the structure and components of our galaxy and of other galaxies. High energy astrophysics – studies phenomena occurring at high energies including active galactic nuclei, gamma-ray bursts and shocks. Interstellar astrophysics – study of the interstellar medium, intergalactic medium and dust. Extragalactic astronomy – study of objects outside our galaxy, including Galaxy formation and evolution.
Stellar astronomy – concerned with Star formation, physical properties, main sequence life span, stellar evolution and extinction. Plasma astrophysics – studies properties of plasma in outer space. Relativistic astrophysics – studies effects of special relativity and general relativity in astrophysical contexts including gravitational waves, gravitational lensing and black holes. Solar physics – Sun and its interaction with the remainder of the Solar System and interstellar space. Planetary Science – study of planets and planetary systems. Atmospheric science – study of atmospheres and weather. Exoplanetology – various planets outside of the Solar System Planetary formation – formation of planets and moons in the context of the formation and evolution of the Solar System. Planetary rings – dynamics and composition of planetary rings Magnetospheres – magnetic fields of planets and moons Planetary surfaces – surface geology of planets and moons Planetary interiors – interior composition of planets and moons Small Solar System bodies – smallest gravitationally bound bodies, including asteroids and Kuiper belt objects.
Astronomy divided by general technique used for astronomical research: Astrometry – study of the position of objects in the sky and their changes of position. Defines the system of coordinates the kinematics of objects in our galaxy. Observational astronomy – practice of observing celestial objects by using telescopes and other astronomical apparatus, it is concerned with recording data. The subdisciplines of observational astronomy are made by the specifications of the detectors: Radio astronomy – Above 300 µm Submillimetre astronomy – 200 µm to 1 mm Infrared astronomy – 0.7–350 µm Optical astronomy – 380–750 nm Ultraviolet astronomy – 10–320 nm X-ray astronomy – 0.01–10 nm Gamma-ray astronomy – Below 0.01 nm Cosmic ray astronomy – Cosmic rays, including plasma Neutrino astronomy – Neutrinos Gravitational wave astronomy – Gravitons Photometry – study of how bright celestial objects are when passed through different filters Spectroscopy – study of the spectra of astronomical objects Other disciplines that may be considered part of astronomy: Archaeoastronomy Astrochemistry Astronomical object Solar System Geology of solar terrestrial planets List of Solar System objects List of Solar System objects by size Galilean satellites Halley's comet Extrasolar planet – planet outside the Solar System.
A total of 899 such planets have been identified as of 27 June 2013. Super-Earth – Constellation Galaxy Andromeda Galaxy Magellanic Clouds Quasar See: Outline of space exploration Space agencies Algerian Space Agency National Authority for Remote Sensing and Space Sciences Egypt Remote Sensing Center Royal Centre for Remote Sensing National Remote Sensing Center National Space Research and Development Agency South African National Space Agency Canadian Space Agency Agencia Espacial Mexicana United States Department of Defense NASA Comisión Nacional de Actividades Espaciales Brazilian Space Agency Brazilian General Command for Aerospace Technology National Institute for Space Research Instituto Tecnológico de Aeronáutica Agencia Chilena del Espacio C