Wikipedia

Astronomy

This article is about the scientific study of celestial objects. For other uses, seeAstronomy (disambiguation).
Not to be confused withastrology,a pseudoscience.

Astronomyis anatural sciencethat studiescelestial objectsand thephenomenathat occur in the cosmos. It usesmathematics,physics,andchemistryin order to explain their origin and their overallevolution.Objects of interest includeplanets,moons,stars,nebulae,galaxies,meteoroids,asteroids,andcomets.Relevant phenomena includesupernovaexplosions,gamma ray bursts,quasars,blazars,pulsars,andcosmic microwave background radiation.More generally, astronomy studies everything that originates beyondEarth's atmosphere.Cosmologyis a branch of astronomy that studies theuniverseas a whole.

TheParanal ObservatoryofEuropean Southern Observatoryshooting alaser guide starto theGalactic Center

Astronomy is one of the oldest natural sciences. The early civilizations inrecorded historymade methodical observations of thenight sky.These include theEgyptians,Babylonians,Greeks,Indians,Chinese,Maya,and many ancientindigenous peoples of the Americas.In the past, astronomy included disciplines as diverse asastrometry,celestial navigation,observational astronomy,and the making ofcalendars.

Professional astronomy is split intoobservationalandtheoreticalbranches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.

Astronomy is one of the few sciences in which amateurs play anactive role.This is especially true for the discovery and observation oftransient events.Amateur astronomershave helped with many important discoveries, such as finding new comets.

Etymology

Astronomical Observatory, New South Wales, Australia 1873
19th-centuryQuito Astronomical Observatoryis located 12 minutes south of theEquatorinQuito,Ecuador.[1]

Astronomy(from theGreekἀστρονομίαfromἄστρονastron,"star" and -νομία-nomiafromνόμοςnomos,"law" or "culture" ) means "law of the stars" (or "culture of the stars" depending on the translation). Astronomy should not be confused withastrology,the belief system which claims that human affairs are correlated with the positions of celestial objects.[2]Although thetwo fieldsshare a common origin, they are now entirely distinct.[3]

Use of terms "astronomy" and "astrophysics"

"Astronomy" and "astrophysics"are synonyms.[4][5][6]Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties",[7]while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena".[8]In some cases, as in the introduction of the introductory textbookThe Physical UniversebyFrank Shu,"astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject.[9]However, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics.[4]Some fields, such asastrometry,are purely astronomy rather than also astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics", partly depending on whether the department is historically affiliated with a physics department,[5]and many professionalastronomershave physics rather than astronomy degrees.[6]Some titles of the leading scientific journals in this field includeThe Astronomical Journal,The Astrophysical Journal,andAstronomy & Astrophysics.

History

Main article:History of astronomy
For a chronological guide, seeTimeline of astronomy.
Further information:ArchaeoastronomyandList of astronomers
A celestial map from the 17th century, by the Dutch cartographerFrederik de Wit

Ancient times

In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye. In some locations, early cultures assembled massive artifacts that may have had some astronomical purpose. In addition to their ceremonial uses, theseobservatoriescould be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year.[10]

Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye. As civilizations developed, most notably inEgypt,Mesopotamia,Greece,Persia,India,China,andCentral America,astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to asastrometry.From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon and the Earth in the Universe were explored philosophically. The Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as thegeocentric modelof the Universe, or thePtolemaic system,named afterPtolemy.[11]

The Suryaprajnaptisūtra, a 6th-century BC astronomy text ofJainsat The Schoyen Collection, London. Above: its manuscript fromc. 1500AD.[12]

A particularly important early development was the beginning of mathematical and scientific astronomy, which began amongthe Babylonians,who laid the foundations for the later astronomical traditions that developed in many other civilizations.[13]TheBabyloniansdiscovered thatlunar eclipsesrecurred in a repeating cycle known as asaros.[14]

Greek equatorialsundial,Alexandria on the Oxus,present-day Afghanistan 3rd–2nd century BC

Following the Babylonians, significant advances in astronomy were made inancient Greeceand theHellenisticworld.Greek astronomyis characterized from the start by seeking a rational, physical explanation for celestial phenomena.[15]In the 3rd century BC,Aristarchus of Samosestimated thesize and distance of the Moon and Sun,and he proposed a model of theSolar Systemwhere the Earth and planets rotated around the Sun, now called theheliocentricmodel.[16]In the 2nd century BC,Hipparchusdiscoveredprecession,calculated the size and distance of the Moon and invented the earliest known astronomical devices such as theastrolabe.[17]Hipparchus also created a comprehensive catalog of 1020 stars, and most of theconstellationsof the northern hemisphere derive from Greek astronomy.[18]TheAntikythera mechanism(c. 150–80 BC) was an earlyanalog computerdesigned to calculate the location of theSun,Moon,andplanetsfor a given date. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanicalastronomical clocksappeared in Europe.[19]

Middle Ages

Medieval Europe housed a number of important astronomers.Richard of Wallingford(1292–1336) made major contributions to astronomy andhorology,including the invention of the first astronomical clock, theRectanguluswhich allowed for the measurement of angles between planets and other astronomical bodies, as well as anequatoriumcalled theAlbionwhich could be used for astronomical calculations such aslunar,solarandplanetarylongitudesand could predicteclipses.Nicole Oresme(1320–1382) andJean Buridan(1300–1361) first discussed evidence for the rotation of the Earth, furthermore, Buridan also developed the theory of impetus (predecessor of the modern scientific theory ofinertia) which was able to show planets were capable of motion without the intervention of angels.[20]Georg von Peuerbach(1423–1461) andRegiomontanus(1436–1476) helped make astronomical progress instrumental to Copernicus's development of the heliocentric model decades later.

Astronomy flourished in the Islamic worldand other parts of the world. This led to the emergence of the first astronomicalobservatoriesin theMuslim worldby the early 9th century.[21][22][23]In 964, theAndromeda Galaxy,the largestgalaxyin theLocal Group,was described by the Persian Muslim astronomerAbd al-Rahman al-Sufiin hisBook of Fixed Stars.[24]TheSN 1006supernova,the brightestapparent magnitudestellar event in recorded history, was observed by the Egyptian Arabic astronomerAli ibn RidwanandChinese astronomersin 1006. Iranian scholarAl-Biruniobserved that, contrary toPtolemy,the Sun'sapogee(highest point in the heavens) was mobile, not fixed.[25]Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science includeAl-Battani,Thebit,Abd al-Rahman al-Sufi,Biruni,Abū Ishāq Ibrāhīm al-Zarqālī,Al-Birjandi,and the astronomers of theMaraghehandSamarkandobservatories. Astronomers during that time introduced manyArabic names now used for individual stars.[26][27]

It is also believed that the ruins atGreat ZimbabweandTimbuktu[28]may have housed astronomical observatories.[29]InPost-classicalWest Africa,Astronomers studied the movement of stars and relation to seasons, crafting charts of the heavens as well as precise diagrams of orbits of the other planets based on complex mathematical calculations.SonghaihistorianMahmud Katidocumented ameteor showerin August 1583.[30][31] Europeans had previously believed that there had been no astronomical observation insub-Saharan Africaduring the pre-colonial Middle Ages, but modern discoveries show otherwise.[32][33][34][35]

For over six centuries (from the recovery of ancient learning during the late Middle Ages into the Enlightenment), theRoman Catholic Churchgave more financial and social support to the study of astronomy than probably all other institutions. Among the Church's motives was finding thedate for Easter.[36]

Scientific revolution

Galileo's sketches and observations of theMoonrevealed that the surface was mountainous.
An astronomical chart from an early scientific manuscript,c. 1000

During theRenaissance,Nicolaus Copernicusproposed a heliocentric model of the solar system. His work was defended byGalileo Galileiand expanded upon byJohannes Kepler.Kepler was the first to devise a system that correctly described the details of the motion of the planets around the Sun. However, Kepler did not succeed in formulating a theory behind the laws he wrote down.[37]It wasIsaac Newton,with his invention ofcelestial dynamicsand hislaw of gravitation,who finally explained the motions of the planets. Newton also developed thereflecting telescope.[38]

Improvements in the size and quality of the telescope led to further discoveries. The English astronomerJohn Flamsteedcatalogued over 3000 stars,[39]More extensive star catalogues were produced byNicolas Louis de Lacaille.The astronomerWilliam Herschelmade a detailed catalog of nebulosity and clusters, and in 1781 discovered the planetUranus,the first new planet found.[40]

During the 18–19th centuries, the study of thethree-body problembyLeonhard Euler,Alexis Claude Clairaut,andJean le Rond d'Alembertled to more accurate predictions about the motions of the Moon and planets. This work was further refined byJoseph-Louis LagrangeandPierre Simon Laplace,allowing the masses of the planets and moons to be estimated from their perturbations.[41]

Significant advances in astronomy came about with the introduction of new technology, including thespectroscopeandphotography.Joseph von Fraunhoferdiscovered about 600 bands in the spectrum of the Sun in 1814–15, which, in 1859,Gustav Kirchhoffascribed to the presence of different elements. Stars were proven to be similar to the Earth's own Sun, but with a wide range oftemperatures,masses,and sizes.[26]

The existence of the Earth's galaxy, theMilky Way,as its own group of stars was only proved in the 20th century, along with the existence of "external" galaxies. The observed recession of those galaxies led to the discovery of the expansion of theUniverse.[42]Theoretical astronomy led to speculations on the existence of objects such asblack holesandneutron stars,which have been used to explain such observed phenomena asquasars,pulsars,blazars,andradio galaxies.Physical cosmologymade huge advances during the 20th century. In the early 1900s the model of theBig Bangtheory was formulated, heavily evidenced bycosmic microwave background radiation,Hubble's law,and thecosmological abundances of elements.Space telescopeshave enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.[43]In February 2016, it was revealed that theLIGOproject haddetected evidenceofgravitational wavesin the previous September.[44][45]

Observational astronomy

Main article:Observational astronomy
Overview of types of observational astronomy by observed wavelengths and their observability

The main source of information aboutcelestial bodiesand other objects isvisible light,or more generallyelectromagnetic radiation.[46]Observational astronomy may be categorized according to the corresponding region of theelectromagnetic spectrumon which the observations are made. Some parts of the spectrum can be observed from the Earth's surface, while other parts are only observable from either high altitudes or outside the Earth's atmosphere. Specific information on these subfields is given below.

Radio astronomy

TheVery Large ArrayinNew Mexico,an example of aradio telescope
Main article:Radio astronomy

Radio astronomy uses radiation withwavelengthsgreater than approximately one millimeter, outside the visible range.[47]Radio astronomy is different from most other forms of observational astronomy in that the observedradio wavescan be treated aswavesrather than as discretephotons.Hence, it is relatively easier to measure both theamplitudeandphaseof radio waves, whereas this is not as easily done at shorter wavelengths.[47]

Although someradio wavesare emitted directly by astronomical objects, a product ofthermal emission,most of the radio emission that is observed is the result ofsynchrotron radiation,which is produced whenelectronsorbitmagnetic fields.[47]Additionally, a number ofspectral linesproduced byinterstellar gas,notably thehydrogenspectral line at 21 cm, are observable at radio wavelengths.[9][47]

A wide variety of other objects are observable at radio wavelengths, includingsupernovae,interstellar gas,pulsars,andactive galactic nuclei.[9][47]

Infrared astronomy

ALMAObservatory is one of the highest observatory sites on Earth. Atacama, Chile.[48]
Main article:Infrared astronomy

Infrared astronomy is founded on the detection and analysis ofinfraredradiation, wavelengths longer than red light and outside the range of our vision. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets,circumstellar disksor nebulae whose light is blocked by dust. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded inmolecular cloudsand the cores of galaxies. Observations from theWide-field Infrared Survey Explorer(WISE) have been particularly effective at unveiling numerous galacticprotostarsand their hoststar clusters.[49][50] With the exception of infraredwavelengthsclose to visible light, such radiation is heavily absorbed by the atmosphere, or masked, as the atmosphere itself produces significant infrared emission. Consequently, infrared observatories have to be located in high, dry places on Earth or in space.[51]Some molecules radiate strongly in the infrared. This allows the study of the chemistry of space; more specifically it can detect water in comets.[52]

Optical astronomy

TheSubaru Telescope(left) andKeck Observatory(center) onMauna Kea,both examples of an observatory that operates at near-infrared and visible wavelengths. TheNASA Infrared Telescope Facility(right) is an example of a telescope that operates only at near-infrared wavelengths.
Main article:Optical astronomy

Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy.[53]Images of observations were originally drawn by hand. In the late 19th century and most of the 20th century, images were made using photographic equipment. Modern images are made using digital detectors, particularly usingcharge-coupled devices(CCDs) and recorded on modern medium. Although visible light itself extends from approximately 4000Åto 7000 Å (400nmto 700 nm),[53]that same equipment can be used to observe somenear-ultravioletandnear-infraredradiation.

Ultraviolet astronomy

Main article:Ultraviolet astronomy

Ultraviolet astronomy employsultravioletwavelengths between approximately 100 and 3200 Å (10 to 320 nm).[47]Light at those wavelengths is absorbed by the Earth's atmosphere, requiring observations at these wavelengths to be performed from the upper atmosphere or from space. Ultraviolet astronomy is best suited to the study of thermal radiation and spectral emission lines from hot bluestars(OB stars) that are very bright in this wave band. This includes the blue stars in other galaxies, which have been the targets of several ultraviolet surveys. Other objects commonly observed in ultraviolet light includeplanetary nebulae,supernova remnants,and active galactic nuclei.[47]However, as ultraviolet light is easily absorbed byinterstellar dust,an adjustment of ultraviolet measurements is necessary.[47]

X-ray astronomy

Main article:X-ray astronomy
X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe

X-ray astronomy usesX-ray wavelengths.Typically, X-ray radiation is produced bysynchrotron emission(the result of electrons orbiting magnetic field lines),thermal emission from thin gasesabove 107(10 million)kelvins,andthermal emission from thick gasesabove 107Kelvin.[47]Since X-rays are absorbed by theEarth's atmosphere,all X-ray observations must be performed fromhigh-altitude balloons,rockets,orX-ray astronomy satellites.NotableX-ray sourcesincludeX-ray binaries,pulsars,supernova remnants,elliptical galaxies,clusters of galaxies,andactive galactic nuclei.[47]

Gamma-ray astronomy

Main article:Gamma ray astronomy

Gamma ray astronomy observes astronomical objects at the shortest wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as theCompton Gamma Ray Observatoryor by specialized telescopes calledatmospheric Cherenkov telescopes.[47]The Cherenkov telescopes do not detect the gamma rays directly but instead detect the flashes of visible light produced when gamma rays are absorbed by the Earth's atmosphere.[54]

Mostgamma-rayemitting sources are actuallygamma-ray bursts,objects which only produce gamma radiation for a few milliseconds to thousands of seconds before fading away. Only 10% of gamma-ray sources are non-transient sources. These steady gamma-ray emitters include pulsars,neutron stars,andblack holecandidates such as active galactic nuclei.[47]

Fields not based on the electromagnetic spectrum

In addition to electromagnetic radiation, a few other events originating from great distances may be observed from the Earth.

Inneutrino astronomy,astronomers use heavily shieldedunderground facilitiessuch asSAGE,GALLEX,andKamioka II/IIIfor the detection ofneutrinos.The vast majority of the neutrinos streaming through the Earth originate from theSun,but 24 neutrinos were also detected fromsupernova 1987A.[47]Cosmic rays,which consist of very high energy particles (atomic nuclei) that can decay or be absorbed when they enter the Earth's atmosphere, result in a cascade of secondary particles which can be detected by current observatories.[55]Some futureneutrino detectorsmay also be sensitive to the particles produced when cosmic rays hit the Earth's atmosphere.[47]

Gravitational-wave astronomyis an emerging field of astronomy that employsgravitational-wave detectorsto collect observational data about distant massive objects. A few observatories have been constructed, such as theLaser Interferometer Gravitational ObservatoryLIGO.LIGO made itsfirst detectionon 14 September 2015, observing gravitational waves from abinary black hole.[56]A secondgravitational wavewas detected on 26 December 2015 and additional observations should continue butgravitational wavesrequire extremely sensitive instruments.[57][58]

The combination of observations made using electromagnetic radiation, neutrinos or gravitational waves and other complementary information, is known asmulti-messenger astronomy.[59][60]

Astrometry and celestial mechanics

Main articles:AstrometryandCelestial mechanics
Star clusterPismis 24with a nebula

One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects. Historically, accurate knowledge of the positions of the Sun, Moon, planets and stars has been essential incelestial navigation(the use of celestial objects to guide navigation) and in the making ofcalendars.[61]: 39 

Careful measurement of the positions of the planets has led to a solid understanding of gravitationalperturbations,and an ability to determine past and future positions of the planets with great accuracy, a field known ascelestial mechanics.More recently the tracking ofnear-Earth objectswill allow for predictions of close encounters or potential collisions of the Earth with those objects.[62]

The measurement ofstellar parallaxof nearby stars provides a fundamental baseline in thecosmic distance ladderthat is used to measure the scale of the Universe. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared. Measurements of theradial velocityandproper motionof stars allow astronomers to plot the movement of these systems through the Milky Way galaxy. Astrometric results are the basis used to calculate the distribution of speculateddark matterin the galaxy.[63]

During the 1990s, the measurement of thestellar wobbleof nearby stars wasused to detectlargeextrasolar planetsorbiting those stars.[64]

Theoretical astronomy

Main article:Theoretical astronomy

Theoretical astronomers use several tools includinganalytical modelsandcomputationalnumerical simulations;each has its particular advantages. Analytical models of a process are better for giving broader insight into the heart of what is going on. Numerical models reveal the existence of phenomena and effects otherwise unobserved.[65][66]

Theorists in astronomy endeavor to create theoretical models that are based on existing observations and known physics, and to predict observational consequences of those models. The observation of phenomena predicted by a model allows astronomers to select between several alternative or conflicting models. Theorists also modify existing models to take into account new observations. In some cases, a large amount of observational data that is inconsistent with a model may lead to abandoning it largely or completely, as forgeocentric theory,the existence ofluminiferous aether,and thesteady-state modelof cosmic evolution.

Phenomena modeled by theoretical astronomers include:

Modern theoretical astronomy reflects dramatic advances in observation since the 1990s, including studies of thecosmic microwave background,distantsupernovaeandgalaxy redshifts,which have led to the development of astandard model of cosmology.This model requires the universe to contain large amounts ofdark matteranddark energywhose nature is currently not well understood, but the model gives detailed predictions that are in excellent agreement with many diverse observations.[67]

Specific subfields

Astrophysics

Main article:Astrophysics
Astrophysics appliesphysicsandchemistryto understand the measurements made by astronomy. Representation of the Observable Universe that includes images fromHubbleand othertelescopes.

Astrophysics is the branch of astronomy that employs the principles of physics andchemistry"to ascertain the nature of theastronomical objects,rather than their positions or motions in space ".[68][69]Among the objects studied are theSun,otherstars,galaxies,extrasolar planets,theinterstellar mediumand thecosmic microwave background.[70][71]Their emissions are examined across all parts of theelectromagnetic spectrum,and the properties examined includeluminosity,density,temperature,andchemicalcomposition. Because astrophysics is a very broad subject,astrophysiciststypically apply many disciplines of physics, includingmechanics,electromagnetism,statistical mechanics,thermodynamics,quantum mechanics,relativity,nuclearandparticle physics,andatomic and molecular physics.

In practice, modern astronomical research often involves a substantial amount of work in the realms oftheoreticaland observational physics. Some areas of study for astrophysicists include their attempts to determine the properties ofdark matter,dark energy,andblack holes;whether or nottime travelis possible,wormholescan form, or themultiverseexists; and theoriginandultimate fate of the universe.[70]Topics also studied by theoretical astrophysicists includeSolar System formation and evolution;stellar dynamicsandevolution;galaxy formation and evolution;magnetohydrodynamics;large-scale structureofmatterin the universe; origin ofcosmic rays;general relativityandphysical cosmology,includingstringcosmology andastroparticle physics.

Astrochemistry

Main article:Astrochemistry

Astrochemistry is the study of the abundance and reactions ofmoleculesin theUniverse,and their interaction withradiation.The discipline is an overlap of astronomy andchemistry.The word "astrochemistry" may be applied to both theSolar Systemand theinterstellar medium.The study of the abundance of elements andisotoperatios in Solar System objects, such asmeteorites,is also calledcosmochemistry,while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate ofmolecular gas cloudsis of special interest, because it is from these clouds that solar systems form. Studies in this field contribute to the understanding of theformation of the Solar System,Earth's origin and geology,abiogenesis,and the origin of climate and oceans.[72]

Astrobiology

Main article:Astrobiology

Astrobiology is an interdisciplinary scientific field concerned with theorigins,early evolution,distribution, and future oflifein theuniverse.Astrobiology considers the question of whetherextraterrestrial lifeexists, and how humans can detect it if it does.[73]The term exobiology is similar.[74]

Astrobiology makes use ofmolecular biology,biophysics,biochemistry,chemistry,astronomy,physical cosmology,exoplanetologyandgeologyto investigate the possibility of life on other worlds and help recognizebiospheresthat might be different from that on Earth.[75]The originand early evolution of life is an inseparable part of the discipline of astrobiology.[76]Astrobiology concerns itself with interpretation of existingscientific data,and although speculation is entertained to give context, astrobiology concerns itself primarily withhypothesesthat fit firmly into existingscientific theories.

Thisinterdisciplinaryfield encompasses research on the origin ofplanetary systems,origins oforganic compounds in space,rock-water-carbon interactions,abiogenesison Earth,planetary habitability,research onbiosignaturesfor life detection, and studies on the potential forlife to adapt to challengeson Earth and inouter space.[77][78][79]

Physical cosmology

Main article:Physical cosmology

Cosmology(from the Greekκόσμος(kosmos) "world, universe" andλόγος(logos) "word, study" or literally "logic" ) could be considered the study of the Universe as a whole.

Hubble Extreme Deep Field

Observations of thelarge-scale structure of the Universe,a branch known asphysical cosmology,have provided a deep understanding of the formation and evolution of the cosmos. Fundamental to modern cosmology is the well-accepted theory of theBig Bang,wherein our Universe began at a singlepoint in time,and thereafterexpandedover the course of 13.8 billion years[80]to its present condition.[81]The concept of the Big Bang can be traced back to the discovery of themicrowave background radiationin 1965.[81]

In the course of this expansion, the Universe underwent several evolutionary stages. In the very early moments, it is theorized that the Universe experienced a very rapidcosmic inflation,which homogenized the starting conditions. Thereafter,nucleosynthesisproduced the elemental abundance of the early Universe.[81](See alsonucleocosmochronology.)

When the first neutralatomsformed from a sea of primordial ions, space became transparent to radiation, releasing the energy viewed today as the microwave background radiation. The expanding Universe then underwent a Dark Age due to the lack of stellar energy sources.[82]

A hierarchical structure of matter began to form from minute variations in the mass density of space. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars, thePopulation III stars.These massive stars triggered thereionizationprocess and are believed to have created many of the heavy elements in the early Universe, which, through nuclear decay, create lighter elements, allowing the cycle of nucleosynthesis to continue longer.[83]

Gravitational aggregations clustered into filaments, leaving voids in the gaps. Gradually, organizations of gas and dust merged to form the first primitive galaxies. Over time, these pulled in more matter, and were often organized intogroups and clustersof galaxies, then into larger-scale superclusters.[84]

Fundamental to the structure of the Universe is the existence ofdark matteranddark energy.These are now thought to be its dominant components, forming 96% of the mass of the Universe. For this reason, much effort is expended in trying to understand the physics of these components.[85]

Extragalactic astronomy

This image shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by thegravitational lenseffect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.
Main article:Extragalactic astronomy

The study of objects outside our galaxy is a branch of astronomy concerned with theformation and evolution of galaxies,their morphology (description) andclassification,the observation ofactive galaxies,and at a larger scale, thegroups and clusters of galaxies.Finally, the latter is important for the understanding of thelarge-scale structure of the cosmos.[61]

Mostgalaxiesare organized into distinct shapes that allow for classification schemes. They are commonly divided intospiral,ellipticalandIrregulargalaxies.[86]

As the name suggests, an elliptical galaxy has the cross-sectional shape of anellipse.The stars move alongrandomorbits with no preferred direction. These galaxies contain little or no interstellar dust, few star-forming regions, and older stars.[61]: 877–878 Elliptical galaxies may have been formed by other galaxies merging.[61]: 939 

A spiral galaxy is organized into a flat, rotating disk, usually with a prominent bulge or bar at the center, and trailing bright arms that spiral outward. The arms are dusty regions of star formation within which massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Both theMilky Wayand one of our nearest galaxy neighbors, theAndromeda Galaxy,are spiral galaxies.[61]: 875 

Irregular galaxies are chaotic in appearance, and are neither spiral nor elliptical.[61]: 879 About a quarter of all galaxies are irregular, and the peculiar shapes of such galaxies may be the result of gravitational interaction.[87]

An active galaxy is a formation that emits a significant amount of its energy from a source other than its stars, dust and gas. It is powered by a compact region at the core, thought to be a supermassive black hole that is emitting radiation from in-falling material.[61]: 907 Aradio galaxyis an active galaxy that is very luminous in the radio portion of the spectrum, and is emitting immense plumes or lobes of gas. Active galaxies that emit shorter frequency, high-energy radiation includeSeyfert galaxies,quasars,andblazars.Quasars are believed to be the most consistently luminous objects in the known universe.[88]

Thelarge-scale structure of the cosmosis represented by groups and clusters of galaxies. This structure is organized into a hierarchy of groupings, with the largest being thesuperclusters.The collective matter is formed intofilamentsand walls, leaving largevoidsbetween.[89]

Galactic astronomy

Observed structure of theMilky Way's spiral arms
Main article:Galactic astronomy

TheSolar Systemorbits within theMilky Way,abarred spiral galaxythat is a prominent member of theLocal Groupof galaxies. It is a rotating mass of gas, dust, stars and other objects, held together by mutual gravitational attraction. As the Earth is located within the dusty outer arms, there are large portions of the Milky Way that are obscured from view.[61]: 837–842, 944 

In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be asupermassive black holeat its center. This is surrounded by four primary arms that spiral from the core. This is a region of active star formation that contains many younger,population Istars. The disk is surrounded by aspheroid haloof older,population IIstars, as well as relatively dense concentrations of stars known asglobular clusters.[90]

Between the stars lies theinterstellar medium,a region of sparse matter. In the densest regions,molecular cloudsofmolecular hydrogenand other elements create star-forming regions. These begin as a compactpre-stellar coreordark nebulae,which concentrate and collapse (in volumes determined by theJeans length) to form compact protostars.[91]

As the more massive stars appear, they transform the cloud into anH II region(ionized atomic hydrogen) of glowing gas and plasma. Thestellar windand supernova explosions from these stars eventually cause the cloud to disperse, often leaving behind one or more youngopen clustersof stars. These clusters gradually disperse, and the stars join the population of the Milky Way.[92]

Kinematic studies of matter in the Milky Way and other galaxies have demonstrated that there is more mass than can be accounted for by visible matter. Adark matter haloappears to dominate the mass, although the nature of this dark matter remains undetermined.[93]

Stellar astronomy

Mz 3,often referred to as the Ant planetary nebula. Ejecting gas from the dying central star shows symmetrical patterns unlike the chaotic patterns of ordinary explosions.
Main article:Star
See also:Solar astronomy

The study of stars andstellar evolutionis fundamental to our understanding of the Universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior.[94]Star formationoccurs in dense regions of dust and gas, known asgiant molecular clouds.When destabilized, cloud fragments can collapse under the influence of gravity, to form aprotostar.A sufficiently dense, and hot, core region will triggernuclear fusion,thus creating amain-sequence star.[91]

Almost all elements heavier thanhydrogenandheliumwerecreatedinside the cores of stars.[94]

The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it fuses its hydrogen fuel into helium in its core. Over time, this hydrogen fuel is completely converted into helium, and the star begins toevolve.The fusion of helium requires a higher core temperature. A star with a high enough core temperature will push its outer layers outward while increasing its core density. The resultingred giantformed by the expanding outer layers enjoys a brief life span, before the helium fuel in the core is in turn consumed. Very massive stars can also undergo a series of evolutionary phases, as they fuse increasingly heavier elements.[95]

The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapsesupernovae;[96]while smaller stars blow off their outer layers and leave behind the inert core in the form of awhite dwarf.The ejection of the outer layers forms aplanetary nebula.[97]The remnant of a supernova is a denseneutron star,or, if the stellar mass was at least three times that of the Sun, ablack hole.[98]Closely orbiting binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova.[99]Planetary nebulae and supernovae distribute the "metals"produced in the star by fusion to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone.[100]

Solar astronomy

Anultravioletimage of the Sun's activephotosphereas viewed by theTRACEspace telescope.NASAphoto
Solar observatoryLomnický štít(Slovakia) built in 1962
Main article:Sun
See also:Solar telescope

At a distance of about eight light-minutes, the most frequently studied star is theSun,a typical main-sequencedwarf starofstellar classG2 V, and about 4.6 billion years (Gyr) old. The Sun is not considered avariable star,but it does undergo periodic changes in activity known as thesunspot cycle.This is an 11-year oscillation insunspot number.Sunspots are regions of lower-than- average temperatures that are associated with intense magnetic activity.[101]

The Sun has steadily increased in luminosity by 40% since it first became a main-sequence star. The Sun has also undergone periodic changes in luminosity that can have a significant impact on the Earth.[102]TheMaunder minimum,for example, is believed to have caused theLittle Ice Agephenomenon during theMiddle Ages.[103]

At the center of the Sun is the core region, a volume of sufficient temperature and pressure fornuclear fusionto occur. Above the core is theradiation zone,where the plasma conveys the energy flux by means of radiation. Above that is theconvection zonewhere the gas material transports energy primarily through physical displacement of the gas known as convection. It is believed that the movement of mass within the convection zone creates the magnetic activity that generates sunspots.[101]The visible outer surface of the Sun is called thephotosphere.Above this layer is a thin region known as thechromosphere.This is surrounded by a transition region of rapidly increasing temperatures, and finally by the super-heatedcorona.[61]: 498–502 

A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches theheliopause.As the solar wind passes the Earth, it interacts with theEarth's magnetic field(magnetosphere) and deflects the solar wind, but traps some creating theVan Allen radiation beltsthat envelop the Earth. Theauroraare created when solar wind particles are guided by the magnetic flux lines into the Earth's polar regions where the lines then descend into theatmosphere.[104]

Planetary science

The black spot at the top is adust devilclimbing a crater wall onMars.This moving, swirling column ofMartian atmosphere(comparable to a terrestrialtornado) created the long, dark streak.
Main articles:Planetary scienceandPlanetary geology

Planetary science is the study of the assemblage ofplanets,moons,dwarf planets,comets,asteroids,and other bodies orbiting the Sun, as well as extrasolar planets. TheSolar Systemhas been relatively well-studied, initially through telescopes and then later by spacecraft. This has provided a good overall understanding of the formation and evolution of the Sun's planetary system, although many new discoveries are still being made.[105]

The Solar System is divided into theinner Solar System(subdivided into the inner planets and theasteroid belt), theouter Solar System(subdivided into the outer planets andcentaurs), comets, the trans-Neptunian region (subdivided into theKuiper belt,and thescattered disc) and the farthest regions (e.g., boundaries of theheliosphere,and theOort Cloud,which may extend as far as a light-year). The innerterrestrial planetsconsist ofMercury,Venus,Earth, andMars.The outergiant planetsare thegas giants(JupiterandSaturn) and theice giants(UranusandNeptune).[106]

The planets were formed 4.6 billion years ago in theprotoplanetary diskthat surrounded the early Sun. Through a process that included gravitational attraction, collision, and accretion, the disk formed clumps of matter that, with time, became protoplanets. Theradiation pressureof thesolar windthen expelled most of the unaccreted matter, and only those planets with sufficient mass retained their gaseous atmosphere. The planets continued to sweep up, or eject, the remaining matter during a period of intense bombardment, evidenced by the manyimpact craterson the Moon. During this period, some of the protoplanets may have collided and one such collision may haveformed the Moon.[107]

Once a planet reaches sufficient mass, the materials of different densities segregate within, duringplanetary differentiation.This process can form a stony or metallic core, surrounded by a mantle and an outer crust. The core may include solid and liquid regions, and some planetary cores generate their ownmagnetic field,which can protect their atmospheres from solar wind stripping.[108]

A planet or moon's interior heat is produced from the collisions that created the body, by the decay of radioactive materials (e.g.uranium,thorium,and26Al), ortidal heatingcaused by interactions with other bodies. Some planets and moons accumulate enough heat to drive geologic processes such asvolcanismand tectonics. Those that accumulate or retain anatmospherecan also undergo surfaceerosionfrom wind or water. Smaller bodies, without tidal heating, cool more quickly; and their geological activity ceases with the exception of impact cratering.[109]

Interdisciplinary studies

Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields.Archaeoastronomyis the study of ancient or traditional astronomies in their cultural context, utilizingarchaeologicalandanthropologicalevidence.Astrobiologyis the study of the advent and evolution of biological systems in the Universe, with particular emphasis on the possibility of non-terrestrial life.Astrostatisticsis the application of statistics to astrophysics to the analysis of a vast amount of observational astrophysical data.[110]

The study ofchemicalsfound in space, including their formation, interaction and destruction, is calledastrochemistry.These substances are usually found inmolecular clouds,although they may also appear in low-temperature stars, brown dwarfs and planets.Cosmochemistryis the study of the chemicals found within the Solar System, including the origins of the elements and variations in theisotoperatios. Both of these fields represent an overlap of the disciplines of astronomy and chemistry. As "forensic astronomy",finally, methods from astronomy have been used to solve problems of art history[111][112]and occasionally of law.[113]

Amateur astronomy

Amateur astronomers can build their own equipment, and hold star parties and gatherings, such asStellafane.
Main article:Amateur astronomy

Astronomy is one of the sciences to which amateurs can contribute the most.[114]

Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with consumer-level equipment orequipment that they build themselves.Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets,meteor showers,and a variety ofdeep-sky objectssuch as star clusters, galaxies, and nebulae. Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to observe all the objects in the Messier (110 objects) or Herschel 400 catalogues of points of interest in the night sky. One branch of amateur astronomy,astrophotography,involves the taking of photos of the night sky. Many amateurs like to specialize in the observation of particular objects, types of objects, or types of events that interest them.[115][116]

Most amateurs work at visible wavelengths, but many experiment with wavelengths outside the visible spectrum. This includes the use of infrared filters on conventional telescopes, and also the use of radio telescopes. The pioneer of amateur radio astronomy wasKarl Jansky,who started observing the sky at radio wavelengths in the 1930s. A number of amateur astronomers use either homemade telescopes or use radio telescopes which were originally built for astronomy research but which are now available to amateurs (e.g.theOne-Mile Telescope).[117][118]

Amateur astronomers continue to make scientific contributions to the field of astronomy and it is one of the few scientific disciplines where amateurs can still make significant contributions. Amateurs can make occultation measurements that are used to refine the orbits of minor planets. They can also discover comets, and perform regular observations of variable stars. Improvements in digital technology have allowed amateurs to make impressive advances in the field of astrophotography.[119][120][121]

Unsolved problems in astronomy

Main article:List of unsolved problems in astronomy

In the 21st century there remain important unanswered questions in astronomy. Some are cosmic in scope: for example, what aredark matteranddark energy?These dominate the evolution and fate of the cosmos, yet their true nature remains unknown.[122]What will be theultimate fate of the universe?[123]Why is the abundance oflithiumin the cosmos four times lower than predicted by the standardBig Bangmodel?[124]Others pertain to more specific classes of phenomena. For example, is theSolar Systemnormal or atypical?[125]What is the origin of the stellar mass spectrum? That is, why do astronomers observe the same distribution of stellar masses—theinitial mass function—apparently regardless of the initial conditions?[126]Likewise, questions remain about the formation of thefirst galaxies,[127]the origin ofsupermassive black holes,[128]the source ofultra-high-energy cosmic rays,[129]and more.

Is there otherlife in the Universe?Especially, is there other intelligent life? If so, what is the explanation for theFermi paradox?The existence of life elsewhere has important scientific and philosophical implications.[130][131]

See also

Lists

References

  1. ^"Inicio"(in Spanish).Quito Astronomical Observatory.Archivedfrom the original on 28 March 2018.
  2. ^Losev, Alexandre (2012). "'Astronomy' or 'astrology': A brief history of an apparent confusion ".Journal of Astronomical History and Heritage.15(1): 42–46.arXiv:1006.5209.Bibcode:2012JAHH...15...42L.doi:10.3724/SP.J.1440-2807.2012.01.05.S2CID51802196.
  3. ^Unsöld, Albrecht; Baschek, Bodo (2001).The New Cosmos: An Introduction to Astronomy and Astrophysics.Translated by Brewer, W.D. Berlin, New York: Springer.ISBN978-3-540-67877-9.
  4. ^abScharringhausen, B. (January 2002)."What is the difference between astronomy and astrophysics?".Curious About Astronomy.Archived fromthe originalon 9 June 2007.Retrieved17 November2016.
  5. ^abOdenwald, Sten."Archive of Astronomy Questions and Answers: What is the difference between astronomy and astrophysics?".The Astronomy Cafe. Archived fromthe originalon 8 July 2007.Retrieved20 June2007.
  6. ^ab"School of Science-Astronomy and Astrophysics".Penn State Erie.18 July 2005. Archived fromthe originalon 1 November 2007.Retrieved20 June2007.
  7. ^"astronomy".Merriam-Webster Online.Archivedfrom the original on 17 June 2007.Retrieved20 June2007.
  8. ^"astrophysics".Merriam-Webster Online.Archivedfrom the original on 21 September 2012.Retrieved20 June2007.
  9. ^abcShu, F.H. (1983).The Physical Universe.Mill Valley, California: University Science Books.ISBN978-0-935702-05-7.
  10. ^Forbes, George (1909).History of Astronomy.London: Plain Label Books.ISBN978-1-60303-159-2.Archivedfrom the original on 28 August 2018.Retrieved7 April2019.
  11. ^DeWitt, Richard (2010). "The Ptolemaic System".Worldviews: An Introduction to the History and Philosophy of Science.Chichester, England: Wiley. p. 113.ISBN978-1-4051-9563-8.
  12. ^SuryaprajnaptiSūtraArchived15 June 2017 at theWayback Machine,The Schoyen Collection, London/Oslo
  13. ^Aaboe, A. (1974). "Scientific Astronomy in Antiquity".Philosophical Transactions of the Royal Society.276(1257): 21–42.Bibcode:1974RSPTA.276...21A.doi:10.1098/rsta.1974.0007.JSTOR74272.S2CID122508567.
  14. ^"Eclipses and the Saros".NASA. Archived fromthe originalon 30 October 2007.Retrieved28 October2007.
  15. ^Krafft, Fritz (2009). "Astronomy". In Cancik, Hubert; Schneider, Helmuth (eds.).Brill's New Pauly.
  16. ^Berrgren, J.L.; Sidoli, Nathan (May 2007). "Aristarchus's On the Sizes and Distances of the Sun and the Moon: Greek and Arabic Texts".Archive for History of Exact Sciences.61(3): 213–54.doi:10.1007/s00407-006-0118-4.S2CID121872685.
  17. ^"Hipparchus of Rhodes".School of Mathematics and Statistics,University of St Andrews,Scotland.Archivedfrom the original on 23 October 2007.Retrieved28 October2007.
  18. ^Thurston, H. (1996).Early Astronomy.Springer Science & Business Media. p. 2.ISBN978-0-387-94822-5.Archivedfrom the original on 3 February 2021.Retrieved20 June2015.
  19. ^Marchant, Jo (2006)."In search of lost time".Nature.444(7119): 534–38.Bibcode:2006Natur.444..534M.doi:10.1038/444534a.PMID17136067.
  20. ^Hannam, James.God's philosophers: how the medieval world laid the foundations of modern science.Icon Books Ltd, 2009, 180
  21. ^Kennedy, Edward S. (1962). "Review:The Observatory in Islam and Its Place in the General History of the Observatoryby Aydin Sayili ".Isis.53(2): 237–39.doi:10.1086/349558.
  22. ^Micheau, Françoise. Rashed, Roshdi; Morelon, Régis (eds.). "The Scientific Institutions in the Medieval Near East".Encyclopedia of the History of Arabic Science.3:992–93.
  23. ^Nas, Peter J (1993).Urban Symbolism.Brill Academic Publishers. p. 350.ISBN978-90-04-09855-8.
  24. ^Kepple, George Robert; Sanner, Glen W. (1998).The Night Sky Observer's Guide.Vol. 1. Willmann-Bell, Inc. p. 18.ISBN978-0-943396-58-3.
  25. ^Covington, Richard (2007)."Rediscovering Arabic Science".Aramco World.Vol. 58, no. 3.Archivedfrom the original on 1 March 2021.Retrieved6 March2023.
  26. ^abBerry, Arthur (1961).A Short History of Astronomy From Earliest Times Through the 19th Century.New York: Dover Publications, Inc.ISBN978-0-486-20210-5.
  27. ^Hoskin, Michael, ed. (1999).The Cambridge Concise History of Astronomy.Cambridge University Press.ISBN978-0-521-57600-0.
  28. ^McKissack, Pat; McKissack, Frederick (1995).The royal kingdoms of Ghana, Mali, and Songhay: life in medieval Africa.H. Holt. p.103.ISBN978-0-8050-4259-7.
  29. ^Clark, Stuart; Carrington, Damian (2002)."Eclipse brings claim of medieval African observatory".New Scientist.Archivedfrom the original on 30 April 2015.Retrieved3 February2010.
  30. ^Hammer, Joshua (2016).The Bad-Ass Librarians of Timbuktu And Their Race to Save the World's Most Precious Manuscripts.New York: Simon & Schuster. pp. 26–27.ISBN978-1-4767-7743-6.
  31. ^Holbrook, Jarita C.; Medupe, R. Thebe;Johnson Urama(2008).African Cultural Astronomy.Springer.ISBN978-1-4020-6638-2.Archivedfrom the original on 17 August 2021.Retrieved19 October2020.
  32. ^"Cosmic Africa explores Africa's astronomy".Science in Africa. Archived fromthe originalon 3 December 2003.Retrieved3 February2002.
  33. ^Holbrook, Jarita C.; Medupe, R. Thebe; Urama, Johnson O. (2008).African Cultural Astronomy.Springer.ISBN978-1-4020-6638-2.Archivedfrom the original on 26 August 2016.Retrieved26 August2020.
  34. ^"Africans studied astronomy in medieval times".The Royal Society. 30 January 2006. Archived fromthe originalon 9 June 2008.Retrieved3 February2010.
  35. ^Stenger, Richard"Star sheds light on African 'Stonehenge'".CNN.5 December 2002. Archived fromthe originalon 12 May 2011..CNN. 5 December 2002. Retrieved on 30 December 2011.
  36. ^J.L. Heilbron,The Sun in the Church: Cathedrals as Solar Observatories(1999), p. 3
  37. ^Forbes 1909,pp. 49–58
  38. ^Forbes 1909,pp. 58–64
  39. ^Chambers, Robert (1864)Chambers Book of Days
  40. ^Forbes 1909,pp. 79–81
  41. ^Forbes 1909,pp. 74–76
  42. ^Belkora, Leila (2003).Minding the heavens: the story of our discovery of the Milky Way.CRC Press.pp. 1–14.ISBN978-0-7503-0730-7.Archivedfrom the original on 27 October 2020.Retrieved26 August2020.
  43. ^McLean, Ian S. (2008). "Beating the atmosphere".Electronic Imaging in Astronomy.Springer Praxis Books. Berlin, Heidelberg: Springer. pp. 39–75.doi:10.1007/978-3-540-76583-7_2.ISBN978-3-540-76582-0.
  44. ^Castelvecchi, Davide; Witze, Witze (11 February 2016)."Einstein's gravitational waves found at last".Nature News.doi:10.1038/nature.2016.19361.S2CID182916902.Archivedfrom the original on 12 February 2016.Retrieved11 February2016.
  45. ^B.P. Abbott; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). "Observation of Gravitational Waves from a Binary Black Hole Merger".Physical Review Letters.116(6): 061102.arXiv:1602.03837.Bibcode:2016PhRvL.116f1102A.doi:10.1103/PhysRevLett.116.061102.PMID26918975.S2CID124959784.
  46. ^"Electromagnetic Spectrum".NASA. Archived fromthe originalon 5 September 2006.Retrieved17 November2016.
  47. ^abcdefghijklmnCox, A.N., ed. (2000).Allen's Astrophysical Quantities.New York: Springer-Verlag. p. 124.ISBN978-0-387-98746-0.Archivedfrom the original on 19 November 2020.Retrieved26 August2020.
  48. ^"In Search of Space".Picture of the Week.European Southern Observatory.Archivedfrom the original on 13 August 2020.Retrieved5 August2014.
  49. ^"Wide-field Infrared Survey Explorer Mission".NASAUniversity of California, Berkeley.30 September 2014. Archived fromthe originalon 12 January 2010.Retrieved17 November2016.
  50. ^Majaess, D. (2013). "Discovering protostars and their host clusters via WISE".Astrophysics and Space Science.344(1): 175–186.arXiv:1211.4032.Bibcode:2013Ap&SS.344..175M.doi:10.1007/s10509-012-1308-y.S2CID118455708.
  51. ^Staff (11 September 2003)."Why infrared astronomy is a hot topic".ESA.Archivedfrom the original on 30 July 2012.Retrieved11 August2008.
  52. ^"Infrared Spectroscopy – An Overview".NASACalifornia Institute of Technology.Archived fromthe originalon 5 October 2008.Retrieved11 August2008.
  53. ^abMoore, P. (1997).Philip's Atlas of the Universe.Great Britain: George Philis Limited.ISBN978-0-540-07465-5.
  54. ^Penston, Margaret J. (14 August 2002)."The electromagnetic spectrum".Particle Physics and Astronomy Research Council. Archived fromthe originalon 8 September 2012.Retrieved17 November2016.
  55. ^Gaisser, Thomas K. (1990).Cosmic Rays and Particle Physics.Cambridge University Press. pp.1–2.ISBN978-0-521-33931-5.
  56. ^Abbott, Benjamin P.; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). "Observation of Gravitational Waves from a Binary Black Hole Merger".Physical Review Letters.116(6): 061102.arXiv:1602.03837.Bibcode:2016PhRvL.116f1102A.doi:10.1103/PhysRevLett.116.061102.PMID26918975.S2CID124959784.
  57. ^Tammann, Gustav-Andreas;Thielemann, Friedrich-Karl;Trautmann, Dirk (2003)."Opening new windows in observing the Universe".Europhysics News. Archived fromthe originalon 6 September 2012.Retrieved17 November2016.
  58. ^LIGO Scientific Collaboration and Virgo Collaboration; Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T. (15 June 2016). "GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence".Physical Review Letters.116(24): 241103.arXiv:1606.04855.Bibcode:2016PhRvL.116x1103A.doi:10.1103/PhysRevLett.116.241103.PMID27367379.S2CID118651851.
  59. ^"Planning for a bright tomorrow: Prospects for gravitational-wave astronomy with Advanced LIGO and Advanced Virgo".LIGO Scientific Collaboration.Archivedfrom the original on 23 April 2016.Retrieved31 December2015.
  60. ^Xing, Zhizhong; Zhou, Shun (2011).Neutrinos in Particle Physics, Astronomy and Cosmology.Springer. p. 313.ISBN978-3-642-17560-2.Archivedfrom the original on 3 February 2021.Retrieved20 June2015.
  61. ^abcdefghiFraknoi, Andrew; et al. (2022).Astronomy 2e(2e ed.). OpenStax.ISBN978-1-951693-50-3.OCLC1322188620.Archivedfrom the original on 23 February 2023.Retrieved16 March2023.
  62. ^Calvert, James B. (28 March 2003)."Celestial Mechanics".University of Denver. Archived fromthe originalon 7 September 2006.Retrieved21 August2006.
  63. ^"Hall of Precision Astrometry".University of VirginiaDepartment of Astronomy. Archived fromthe originalon 26 August 2006.Retrieved17 November2016.
  64. ^Wolszczan, A.; Frail, D. A. (1992). "A planetary system around the millisecond pulsar PSR1257+12".Nature.355(6356): 145–47.Bibcode:1992Natur.355..145W.doi:10.1038/355145a0.S2CID4260368.
  65. ^Roth, H. (1932). "A Slowly Contracting or Expanding Fluid Sphere and its Stability".Physical Review.39(3): 525–29.Bibcode:1932PhRv...39..525R.doi:10.1103/PhysRev.39.525.
  66. ^Eddington, A.S. (1926)."Internal Constitution of the Stars".Science.52(1341). Cambridge University Press: 233–40.Bibcode:1920Sci....52..233E.doi:10.1126/science.52.1341.233.ISBN978-0-521-33708-3.PMID17747682.Archivedfrom the original on 17 August 2021.Retrieved4 November2020.
  67. ^Beringer, J.; et al. (Particle Data Group) (2012)."2013 Review of Particle Physics"(PDF).Phys. Rev. D.86(1): 010001.Bibcode:2012PhRvD..86a0001B.doi:10.1103/PhysRevD.86.010001.Archived(PDF)from the original on 9 October 2022.
  68. ^Keeler, James E.(November 1897)."The Importance of Astrophysical Research and the Relation of Astrophysics to the Other Physical Sciences".The Astrophysical Journal.6(4): 271–88.Bibcode:1897ApJ.....6..271K.doi:10.1086/140401.PMID17796068.[Astrophysics] is closely allied on the one hand to astronomy, of which it may properly be classed as a branch, and on the other hand to chemistry and physics.… It seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—whatthey are, rather thanwherethey are.… That which is perhaps most characteristic of astrophysics is the special prominence which it gives to the study of radiation.
  69. ^"astrophysics".Merriam-Webster, Incorporated.Archivedfrom the original on 10 June 2011.Retrieved22 May2011.
  70. ^ab"Focus Areas – NASA Science".nasa.gov.Archivedfrom the original on 16 May 2017.Retrieved12 November2018.
  71. ^"astronomy".Encyclopædia Britannica.Archivedfrom the original on 10 May 2015.Retrieved12 November2018.
  72. ^"Astrochemistry".cfa.harvard.edu/.15 July 2013. Archived fromthe originalon 20 November 2016.Retrieved20 November2016.
  73. ^"About Astrobiology".NASA Astrobiology Institute.NASA. 21 January 2008. Archived fromthe originalon 11 October 2008.Retrieved20 October2008.
  74. ^Mirriam Webster Dictionary entry "Exobiology"Archived4 September 2018 at theWayback Machine(accessed 11 April 2013)
  75. ^Ward, P.D.; Brownlee, D. (2004).The life and death of planet Earth.New York: Owl Books.ISBN978-0-8050-7512-0.
  76. ^"Origins of Life and Evolution of Biospheres".Journal: Origins of Life and Evolution of Biospheres.Archivedfrom the original on 8 February 2020.Retrieved6 April2015.
  77. ^"Release of the First Roadmap for European Astrobiology".European Science Foundation.Astrobiology Web. 29 March 2016.Archivedfrom the original on 10 June 2020.Retrieved2 April2016.
  78. ^Corum, Jonathan (18 December 2015)."Mapping Saturn's Moons".The New York Times.Archivedfrom the original on 20 May 2020.Retrieved18 December2015.
  79. ^Cockell, Charles S. (4 October 2012)."How the search for aliens can help sustain life on Earth".CNN News.Archivedfrom the original on 10 September 2016.Retrieved8 October2012.
  80. ^"Cosmic Detectives".The European Space Agency (ESA). 2 April 2013.Archivedfrom the original on 11 February 2019.Retrieved15 April2013.
  81. ^abcDodelson, Scott (2003).Modern cosmology.Academic Press.pp. 1–22.ISBN978-0-12-219141-1.
  82. ^Hinshaw, Gary (13 July 2006)."Cosmology 101: The Study of the Universe".NASA WMAP.Archivedfrom the original on 13 August 2006.Retrieved10 August2006.
  83. ^Dodelson, 2003, pp. 216–61
  84. ^"Galaxy Clusters and Large-Scale Structure".University of Cambridge.Archivedfrom the original on 10 October 2006.Retrieved8 September2006.
  85. ^Preuss, Paul."Dark Energy Fills the Cosmos".U.S. Department of Energy, Berkeley Lab.Archivedfrom the original on 11 August 2006.Retrieved8 September2006.
  86. ^Keel, Bill (1 August 2006)."Galaxy Classification".University of Alabama.Archivedfrom the original on 1 September 2006.Retrieved8 September2006.
  87. ^"A lopsided lynx".esahubble.org.European Space Agency.8 August 2016.Archivedfrom the original on 9 July 2021.Retrieved17 March2023.
  88. ^"Active Galaxies and Quasars".NASA. Archived fromthe originalon 31 August 2006.Retrieved17 November2016.
  89. ^Michael Zeilik(2002).Astronomy: The Evolving Universe(8th ed.). Wiley.ISBN978-0-521-80090-7.
  90. ^Ott, Thomas (24 August 2006)."The Galactic Centre".Max-Planck-Institut für extraterrestrische Physik. Archived fromthe originalon 4 September 2006.Retrieved17 November2016.
  91. ^abSmith, Michael David (2004)."Cloud formation, Evolution and Destruction".The Origin of Stars.Imperial College Press. pp. 53–86.ISBN978-1-86094-501-4.Archivedfrom the original on 13 August 2021.Retrieved26 August2020.
  92. ^Smith, Michael David (2004)."Massive stars".The Origin of Stars.Imperial College Press. pp. 185–99.ISBN978-1-86094-501-4.Archivedfrom the original on 13 August 2021.Retrieved26 August2020.
  93. ^Van den Bergh, Sidney (1999). "The Early History of Dark Matter".Publications of the Astronomical Society of the Pacific.111(760): 657–60.arXiv:astro-ph/9904251.Bibcode:1999PASP..111..657V.doi:10.1086/316369.S2CID5640064.
  94. ^abHarpaz, 1994, pp. 7–18
  95. ^Harpaz, 1994
  96. ^Harpaz, 1994, pp. 173–78
  97. ^Harpaz, 1994, pp. 111–18
  98. ^Audouze, Jean; Israel, Guy, eds. (1994).The Cambridge Atlas of Astronomy(3rd ed.). Cambridge University Press.ISBN978-0-521-43438-6.
  99. ^Harpaz, 1994, pp. 189–210
  100. ^Harpaz, 1994, pp. 245–56
  101. ^abJohansson, Sverker(27 July 2003)."The Solar FAQ".Talk.Origins Archive.Archivedfrom the original on 7 September 2006.Retrieved11 August2006.
  102. ^Lerner, K. Lee; Lerner, Brenda Wilmoth (2006)."Environmental issues: essential primary sources".Thomson Gale. Archived fromthe originalon 10 July 2012.Retrieved17 November2016.
  103. ^Pogge, Richard W. (1997)."The Once & Future Sun".New Vistas in Astronomy.Archived fromthe original(lecture notes)on 27 May 2005.Retrieved3 February2010.
  104. ^Stern, D.P.; Peredo, M. (28 September 2004)."The Exploration of the Earth's Magnetosphere".NASA.Archivedfrom the original on 24 August 2006.Retrieved22 August2006.
  105. ^Bell III, J. F.; Campbell, B.A.; Robinson, M.S. (2004).Remote Sensing for the Earth Sciences: Manual of Remote Sensing(3rd ed.). John Wiley & Sons. Archived fromthe originalon 11 August 2006.Retrieved17 November2016.
  106. ^Grayzeck, E.; Williams, D.R. (11 May 2006)."Lunar and Planetary Science".NASA.Archivedfrom the original on 20 August 2006.Retrieved21 August2006.
  107. ^Montmerle, Thierry; Augereau, Jean-Charles; Chaussidon, Marc; et al. (2006). "Solar System Formation and Early Evolution: the First 100 Million Years".Earth, Moon, and Planets.98(1–4): 39–95.Bibcode:2006EM&P...98...39M.doi:10.1007/s11038-006-9087-5.S2CID120504344.
  108. ^Montmerle, 2006, pp. 87–90
  109. ^Beatty, J.K.; Petersen, C.C.; Chaikin, A., eds. (1999).The New Solar System.Cambridge press. p. 70edition = 4th.ISBN978-0-521-64587-4.Archivedfrom the original on 30 March 2015.Retrieved26 August2020.
  110. ^Hilbe, Joseph M. (2017). "Astrostatistics".Wiley StatsRef:Statistics Reference Online.Wiley. pp. 1–5.doi:10.1002/9781118445112.stat07961.ISBN9781118445112.
  111. ^Ouellette, Jennifer (13 May 2016)."Scientists Used the Stars to Confirm When a Famous Sapphic Poem Was Written".Gizmodo.Archivedfrom the original on 24 March 2023.Retrieved24 March2023.
  112. ^Ash, Summer (17 April 2018)."'Forensic Astronomy' Reveals the Secrets of an Iconic Ansel Adams Photo ".Scientific American.Archivedfrom the original on 24 March 2023.Retrieved24 March2023.
  113. ^Marché, Jordan D. (2005)."Epilogue".Theaters of Time and Space: American Planetaria, 1930–1970.Rutgers University Press. pp. 170–178.ISBN0-813-53576-X.JSTORj.ctt5hjd29.14.
  114. ^Mims III, Forrest M. (1999). "Amateur Science—Strong Tradition, Bright Future".Science.284(5411): 55–56.Bibcode:1999Sci...284...55M.doi:10.1126/science.284.5411.55.S2CID162370774.Astronomy has traditionally been among the most fertile fields for serious amateurs [...]
  115. ^"The American Meteor Society".Archivedfrom the original on 22 August 2006.Retrieved24 August2006.
  116. ^Lodriguss, Jerry."Catching the Light: Astrophotography".Archivedfrom the original on 1 September 2006.Retrieved24 August2006.
  117. ^Ghigo, F. (7 February 2006)."Karl Jansky and the Discovery of Cosmic Radio Waves".National Radio Astronomy Observatory.Archivedfrom the original on 31 August 2006.Retrieved24 August2006.
  118. ^"Cambridge Amateur Radio Astronomers".Archivedfrom the original on 24 May 2012.Retrieved24 August2006.
  119. ^"The International Occultation Timing Association".Archived fromthe originalon 21 August 2006.Retrieved24 August2006.
  120. ^"Edgar Wilson Award".IAU Central Bureau for Astronomical Telegrams. Archived fromthe originalon 24 October 2010.Retrieved24 October2010.
  121. ^"American Association of Variable Star Observers".AAVSO.Archivedfrom the original on 2 February 2010.Retrieved3 February2010.
  122. ^"11 Physics Questions for the New Century".Pacific Northwest National Laboratory. Archived fromthe originalon 3 February 2006.Retrieved12 August2006.
  123. ^Hinshaw, Gary (15 December 2005)."What is the Ultimate Fate of the Universe?".NASA WMAP.Archivedfrom the original on 29 May 2007.Retrieved28 May2007.
  124. ^Howk, J. Christopher; Lehner, Nicolas; Fields, Brian D.; Mathews, Grant J. (6 September 2012). "Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud".Nature.489(7414): 121–23.arXiv:1207.3081.Bibcode:2012Natur.489..121H.doi:10.1038/nature11407.PMID22955622.S2CID205230254.
  125. ^Beer, M. E.; King, A. R.; Livio, M.; Pringle, J. E. (November 2004). "How special is the Solar system?".Monthly Notices of the Royal Astronomical Society.354(3): 763–768.arXiv:astro-ph/0407476.Bibcode:2004MNRAS.354..763B.doi:10.1111/j.1365-2966.2004.08237.x.S2CID119552423.
  126. ^Kroupa, Pavel (2002). "The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems".Science.295(5552): 82–91.arXiv:astro-ph/0201098.Bibcode:2002Sci...295...82K.doi:10.1126/science.1067524.PMID11778039.S2CID14084249.
  127. ^"FAQ – How did galaxies form?".NASA. Archived fromthe originalon 28 June 2015.Retrieved28 July2015.
  128. ^"Supermassive Black Hole".Swinburne University.Archivedfrom the original on 14 August 2020.Retrieved28 July2015.
  129. ^Hillas, A.M. (September 1984). "The Origin of Ultra-High-Energy Cosmic Rays".Annual Review of Astronomy and Astrophysics.22:425–44.Bibcode:1984ARA&A..22..425H.doi:10.1146/annurev.aa.22.090184.002233.This poses a challenge to these models, because [...]
  130. ^"Rare Earth: Complex Life Elsewhere in the Universe?".Astrobiology Magazine.15 July 2002. Archived from the original on 28 June 2011.Retrieved12 August2006.{{cite web}}:CS1 maint: unfit URL (link)
  131. ^Sagan, Carl."The Quest for Extraterrestrial Intelligence".Cosmic Search Magazine.Archivedfrom the original on 18 August 2006.Retrieved12 August2006.

Bibliography

Wikimedia Commons has media related toAstronomy.
Wikibooks has more on the topic of:Astronomy

Retrieved from "https://en.wikipedia.org/w/index.php?title=Astronomy&oldid=1230650774"