177-519: The Milky Way is the galaxy that includes the Solar System , with the name describing the galaxy's appearance from Earth : a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye . The Milky Way is a barred spiral galaxy with a D 25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years ), but only about 1,000 light-years thick at
354-483: A conjunction of Jupiter and Mars in 1106 or 1107 as evidence. The Persian astronomer Nasir al-Din al-Tusi (1201–1274) in his Tadhkira wrote: "The Milky Way, i.e. the Galaxy, is made up of a very large number of small, tightly clustered stars, which, on account of their concentration and smallness, seem to be cloudy patches. Because of this, it was likened to milk in color." Ibn Qayyim al-Jawziyya (1292–1350) proposed that
531-647: A radius of about 39.5 kpc (130,000 ly), over twice as much as was determined in earlier studies, suggesting that about 90% of the mass of the galaxy is dark matter . In September 2023, astronomers reported that the virial mass of the Milky Way Galaxy is only 2.06 10 solar masses , only a 10th of the mass of previous studies. The mass was determined from data of the Gaia spacecraft . The Milky Way contains between 100 and 400 billion stars and at least that many planets. An exact figure would depend on counting
708-599: A 2016 study. Such Earth-sized planets may be more numerous than gas giants, though harder to detect at great distances given their small size. Besides exoplanets, " exocomets ", comets beyond the Solar System, have also been detected and may be common in the Milky Way. More recently, in November 2020, over 300 million habitable exoplanets are estimated to exist in the Milky Way Galaxy. When compared to other more distant galaxies in
885-473: A certain sense, therefore, Latin was studied as a dead language, while it was still a living." Also problematic in Teuffel's scheme is its appropriateness to the concept of classical Latin. Cruttwell addresses the issue by altering the concept of the classical. The "best" Latin is defined as "golden" Latin, the second of the three periods. The other two periods (considered "classical") are left hanging. By assigning
1062-452: A chain reaction of star-building that spreads throughout the gaseous region. Only when the available gas is nearly consumed or dispersed does the activity end. Starbursts are often associated with merging or interacting galaxies. The prototype example of such a starburst-forming interaction is M82 , which experienced a close encounter with the larger M81 . Irregular galaxies often exhibit spaced knots of starburst activity. A radio galaxy
1239-606: A debate took place between Harlow Shapley and Heber Curtis , the Great Debate , concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift. In 1922, the Estonian astronomer Ernst Öpik gave
1416-433: A detailed analysis of style, whereas Teuffel was more concerned with history. Like Teuffel, Cruttwell encountered issues while attempting to condense the voluminous details of time periods in an effort to capture the meaning of phases found in their various writing styles. Like Teuffel, he has trouble finding a name for the first of the three periods (the current Old Latin phase), calling it "from Livius to Sulla ." He says
1593-518: A dim un-resolved "milky" glowing band arching across the night sky. The term is a translation of the Classical Latin via lactea , in turn derived from the Hellenistic Greek γαλαξίας , short for γαλαξίας κύκλος ( galaxías kýklos ), meaning "milky circle". The Ancient Greek γαλαξίας ( galaxias ) – from root γαλακτ -, γάλα ("milk") + -ίας (forming adjectives) – is also
1770-524: A distance determination that supported the theory that the Andromeda Nebula is indeed a distant extra-galactic object. Using the new 100-inch Mt. Wilson telescope, Edwin Hubble was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables , thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of
1947-467: A form of Greek that was considered model. Before then, the term classis , in addition to being a naval fleet, was a social class in one of the diachronic divisions of Roman society in accordance with property ownership under the Roman constitution. The word is a transliteration of Greek κλῆσις (clēsis, or "calling") used to rank army draftees by property from first to fifth class. Classicus refers to those in
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#17328374090702124-418: A function of their radius (or distance from their cores) falls off more slowly than their smaller counterparts. The formation of these cD galaxies remains an active area of research, but the leading model is that they are the result of the mergers of smaller galaxies in the environments of dense clusters, or even those outside of clusters with random overdensities. These processes are the mechanisms that drive
2301-453: A great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but very prominent when viewed from rural areas when the Moon is below the horizon. Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of
2478-402: A huge number of stars held together by gravitational forces, akin to the Solar System but on a much larger scale, and that the resulting disk of stars could be seen as a band on the sky from a perspective inside it. In his 1755 treatise, Immanuel Kant elaborated on Wright's idea about the Milky Way's structure. The first project to describe the shape of the Milky Way and the position of
2655-429: A low portion of open clusters and a reduced rate of new star formation. Instead, they are dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions. The stars contain low abundances of heavy elements because star formation ceases after the initial burst. In this sense they have some similarity to the much smaller globular clusters . The largest galaxies are
2832-459: A measurement of the radial velocity of halo stars found that the mass enclosed within 80 kilo parsecs is 7 × 10 M ☉ . In a 2014 study, the mass of the entire Milky Way is estimated to be 8.5 × 10 M ☉ , but this is only half the mass of the Andromeda Galaxy. A recent 2019 mass estimate for the Milky Way is 1.29 × 10 M ☉ . Much of the mass of
3009-403: A mortal woman, the infant Heracles , on Hera 's breast while she is asleep so the baby will drink her divine milk and thus become immortal. Hera wakes up while breastfeeding and then realises she is nursing an unknown baby: she pushes the baby away, some of her milk spills, and it produces the band of light known as the Milky Way. In the astronomical literature, the capitalised word "Galaxy"
3186-552: A part of the Milky Way, but their true composition and natures remained a mystery. Observations using larger telescopes of a few nearby bright galaxies, like the Andromeda Galaxy , began resolving them into huge conglomerations of stars, but based simply on the apparent faintness and sheer population of stars, the true distances of these objects placed them well beyond the Milky Way. For this reason they were popularly called island universes , but this term quickly fell into disuse, as
3363-417: A pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant angular velocity . The spiral arms are thought to be areas of high-density matter, or " density waves ". As stars move through an arm, the space velocity of each stellar system is modified by the gravitational force of
3540-407: A phase of styles. The ancient authors themselves first defined style by recognizing different kinds of sermo , or "speech". By valuing Classical Latin as "first class", it was better to write with Latinitas selected by authors who were attuned to literary and upper-class languages of the city as a standardized style. All sermo that differed from it was a different style. Thus, in rhetoric, Cicero
3717-400: A plane, the majority of mass in spiral galaxies exists in a roughly spherical halo of dark matter which extends beyond the visible component, as demonstrated by the universal rotation curve concept. Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. In
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#17328374090703894-400: A range in mass, as large as 4.5 × 10 M ☉ and as small as 8 × 10 M ☉ . By comparison, the total mass of all the stars in the Milky Way is estimated to be between 4.6 × 10 M ☉ and 6.43 × 10 M ☉ . In addition to the stars, there is also interstellar gas, comprising 90% hydrogen and 10% helium by mass, with two thirds of
4071-438: A reserve of cold gas that forms giant molecular clouds . Some galaxies have been observed to form stars at an exceptional rate, which is known as a starburst . If they continue to do so, they would consume their reserve of gas in a time span less than the galaxy's lifespan. Hence starburst activity usually lasts only about ten million years, a relatively brief period in a galaxy's history. Starburst galaxies were more common during
4248-401: A ring-like filament of stars called Triangulum–Andromeda Ring (TriAnd Ring) rippling above and below the relatively flat galactic plane , which alongside Monoceros Ring were both suggested to be primarily the result of disk oscillations and wrapping around the Milky Way, at a diameter of at least 50 kpc (160,000 ly), which may be part of the Milky Way's outer disk itself, hence making
4425-435: A rotating bar structure in the center of this galaxy. With improved radio telescopes , hydrogen gas could also be traced in other galaxies. In the 1970s, Vera Rubin uncovered a discrepancy between observed galactic rotation speed and that predicted by the visible mass of stars and gas. Today, the galaxy rotation problem is thought to be explained by the presence of large quantities of unseen dark matter . Beginning in
4602-488: A single larger galaxy; the Milky Way has at least a dozen such satellites, with an estimated 300–500 yet to be discovered. Most of the information we have about dwarf galaxies come from observations of the local group , containing two spiral galaxies, the Milky Way and Andromeda, and many dwarf galaxies. These dwarf galaxies are classified as either irregular or dwarf elliptical / dwarf spheroidal galaxies . A study of 27 Milky Way neighbors found that in all dwarf galaxies,
4779-530: A slight alteration in approach, making it clear that his terms applied to Latin and not just to the period. He also changed his dating scheme from AUC to modern BC/AD. Though he introduces das silberne Zeitalter der römischen Literatur , (The Silver Age of Roman Literature) from the death of Augustus to the death of Trajan (14–117 AD), he also mentions parts of a work by Seneca the Elder , a wenig Einfluss der silbernen Latinität (a slight influence of silver Latin). It
4956-419: A smaller companion galaxy—that as the two galaxy centers approach, they start to oscillate around a center point, and the oscillation creates gravitational ripples forming the shells of stars, similar to ripples spreading on water. For example, galaxy NGC 3923 has over 20 shells. Spiral galaxies resemble spiraling pinwheels . Though the stars and other visible material contained in such a galaxy lie mostly on
5133-413: A treatise in 1755, Immanuel Kant , drawing on earlier work by Thomas Wright , speculated (correctly) that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the Solar System but on much larger scales. The resulting disk of stars would be seen as a band on the sky from our perspective inside the disk. Wright and Kant also conjectured that some of
5310-528: Is 3C 236 , with lobes 15 million light-years across. It should however be noted that radio emissions are not always considered part of the main galaxy itself. A giant radio galaxy is a special class of objects characterized by the presence of radio lobes generated by relativistic jets powered by the central galaxy's supermassive black hole . Giant radio galaxies are different from ordinary radio galaxies in that they can extend to much larger scales, reaching upwards to several megaparsecs across, far larger than
5487-729: Is Cruttwell's Augustan Epoch (42 BC – 14 AD). The literary histories list includes all authors from Canonical to the Ciceronian Age—even those whose works are fragmented or missing altogether. With the exception of a few major writers, such as Cicero, Caesar, Virgil and Catullus, ancient accounts of Republican literature praise jurists and orators whose writings, and analyses of various styles of language cannot be verified because there are no surviving records. The reputations of Aquilius Gallus, Quintus Hortensius Hortalus , Lucius Licinius Lucullus , and many others who gained notoriety without readable works, are presumed by their association within
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5664-425: Is a disk of gas and dust called the interstellar medium . This disk has at least a comparable extent in radius to the stars, whereas the thickness of the gas layer ranges from hundreds of light-years for the colder gas to thousands of light-years for warmer gas. The disk of stars in the Milky Way does not have a sharp edge beyond which there are no stars. Rather, the concentration of stars decreases with distance from
5841-512: Is a galaxy with giant regions of radio emission extending well beyond its visible structure. These energetic radio lobes are powered by jets from its active galactic nucleus . Radio galaxies are classified according to their Fanaroff–Riley classification . The FR I class have lower radio luminosity and exhibit structures which are more elongated; the FR II class are higher radio luminosity. The correlation of radio luminosity and structure suggests that
6018-485: Is a spiral galaxy having the number 109 in the catalogue of Messier. It also has the designations NGC 3992, UGC 6937, CGCG 269–023, MCG +09-20-044, and PGC 37617 (or LEDA 37617), among others. Millions of fainter galaxies are known by their identifiers in sky surveys such as the Sloan Digital Sky Survey . Greek philosopher Democritus (450–370 BCE) proposed that the bright band on the night sky known as
6195-562: Is also used to observe distant, red-shifted galaxies that were formed much earlier. Water vapor and carbon dioxide absorb a number of useful portions of the infrared spectrum, so high-altitude or space-based telescopes are used for infrared astronomy . The first non-visual study of galaxies, particularly active galaxies, was made using radio frequencies . The Earth's atmosphere is nearly transparent to radio between 5 MHz and 30 GHz. The ionosphere blocks signals below this range. Large radio interferometers have been used to map
6372-581: Is an intense radio source known as Sagittarius A* , a supermassive black hole of 4.100 (± 0.034) million solar masses . The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang . Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that
6549-470: Is approximately 890 billion to 1.54 trillion times the mass of the Sun in total (8.9 × 10 to 1.54 × 10 solar masses), although stars and planets make up only a small part of this. Estimates of the mass of the Milky Way vary, depending upon the method and data used. The low end of the estimate range is 5.8 × 10 solar masses ( M ☉ ), somewhat less than that of the Andromeda Galaxy . Measurements using
6726-472: Is asleep so the baby will drink her divine milk and become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away, some of her milk spills, and it produces the band of light known as the Milky Way. In another Greek story, the abandoned Heracles is given by Athena to Hera for feeding, but Heracles' forcefulness causes Hera to rip him from her breast in pain. Llys Dôn (literally "The Court of Dôn ")
6903-524: Is called the Galactic Center . The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter . Consequently, these galaxies also have
7080-447: Is called the Zone of Avoidance . The Milky Way has a relatively low surface brightness . Its visibility can be greatly reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is approximately +5.1 or better and shows
7257-520: Is celestial. This idea would be influential later in the Muslim world . The Persian astronomer Al-Biruni (973–1048) proposed that the Milky Way is "a collection of countless fragments of the nature of nebulous stars". The Andalusian astronomer Avempace ( d 1138) proposed that the Milky Way was made up of many stars but appeared to be a continuous image in the Earth's atmosphere, citing his observation of
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7434-443: Is clear that his mindset had shifted from Golden and Silver Ages to Golden and Silver Latin, also to include Latinitas , which at this point must be interpreted as Classical Latin. He may have been influenced in that regard by one of his sources E. Opitz, who in 1852 had published specimen lexilogiae argenteae latinitatis , which includes Silver Latinity. Though Teuffel's First Period was equivalent to Old Latin and his Second Period
7611-498: Is derived from the Greek galaxias ( γαλαξίας ), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System . Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass . Most of
7788-467: Is estimated to contain 100–400 billion stars and at least that number of planets . The Solar System is located at a radius of about 27,000 light-years (8.3 kpc) from the Galactic Center , on the inner edge of the Orion Arm , one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The Galactic Center
7965-604: Is filled with a tenuous gas (the intergalactic medium ) with an average density of less than one atom per cubic metre. Most galaxies are gravitationally organised into groups , clusters and superclusters . The Milky Way is part of the Local Group , which it dominates along with the Andromeda Galaxy . The group is part of the Virgo Supercluster . At the largest scale , these associations are generally arranged into sheets and filaments surrounded by immense voids . Both
8142-457: Is given by the Hubble sequence . Since the Hubble sequence is entirely based upon visual morphological type (shape), it may miss certain important characteristics of galaxies such as star formation rate in starburst galaxies and activity in the cores of active galaxies . Many galaxies are thought to contain a supermassive black hole at their center. This includes the Milky Way, whose core region
8319-470: Is inclined by about 60° to the ecliptic (the plane of Earth's orbit ). Relative to the celestial equator , it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux , indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane. The north galactic pole is situated at right ascension 12 49, declination +27.4° ( B1950 ) near β Comae Berenices , and
8496-467: Is not that of the golden age... Evidently, Teuffel received ideas about golden and silver Latin from an existing tradition and embedded them in a new system, transforming them as he thought best. In Cruttwell's introduction, the Golden Age is dated 80 BC – AD 14 (from Cicero to Ovid ), which corresponds to Teuffel's findings. Of the "Second Period", Cruttwell paraphrases Teuffel by saying it "represents
8673-659: Is often used to refer to the Milky Way galaxy, to distinguish it from the other galaxies in the observable universe . The English term Milky Way can be traced back to a story by Geoffrey Chaucer c. 1380 : See yonder, lo, the Galaxyë Which men clepeth the Milky Wey , For hit is whyt. Galaxies were initially discovered telescopically and were known as spiral nebulae . Most 18th- to 19th-century astronomers considered them as either unresolved star clusters or anagalactic nebulae , and were just thought of as
8850-432: Is significantly smaller than the Andromeda Galaxy's isophotal diameter, and slightly below the mean isophotal sizes of the galaxies being at 28.3 kpc (92,000 ly). The paper concludes that the Milky Way and Andromeda Galaxy were not overly large spiral galaxies, nor were among the largest known (if the former not being the largest) as previously widely believed, but rather average ordinary spiral galaxies. To compare
9027-417: Is sometimes referred to as a flocculent spiral galaxy ; in contrast to the grand design spiral galaxy that has prominent and well-defined spiral arms. The speed in which a galaxy rotates is thought to correlate with the flatness of the disc as some spiral galaxies have thick bulges, while others are thin and dense. In spiral galaxies, the spiral arms do have the shape of approximate logarithmic spirals ,
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#17328374090709204-588: Is that period in which the climax was reached in the perfection of form, and in most respects also in the methodical treatment of the subject-matters. It may be subdivided between the generations, in the first of which (the Ciceronian Age) prose culminated, while poetry was principally developed in the Augustan Age. The Ciceronian Age was dated 671–711 AUC (83–43 BC), ending just after the death of Marcus Tullius Cicero. The Augustan 711–67 AUC (43 BC – 14 AD) ends with
9381-635: Is the Large Sagittarius Star Cloud , a portion of the central bulge of the galaxy. Dark regions within the band, such as the Great Rift and the Coalsack , are areas where interstellar dust blocks light from distant stars. Peoples of the southern hemisphere, including the Inca and Australian aborigines , identified these regions as dark cloud constellations . The area of sky that the Milky Way obscures
9558-583: Is the first known reference (possibly innovated during this time) to Classical Latin applied by authors, evidenced in the authentic language of their works. Imitating Greek grammarians, Romans such as Quintilian drew up lists termed indices or ordines modeled after the ones created by the Greeks, which were called pinakes . The Greek lists were considered classical, or recepti scriptores ("select writers"). Aulus Gellius includes authors like Plautus , who are considered writers of Old Latin and not strictly in
9735-401: Is the traditional Welsh name for the constellation Cassiopeia . At least three of Dôn's children also have astronomical associations: Caer Gwydion ("The fortress of Gwydion ") is the traditional Welsh name for the Milky Way, and Caer Arianrhod ("The Fortress of Arianrhod ") being the constellation of Corona Borealis . In Western culture, the name "Milky Way" is derived from its appearance as
9912-483: Is visible as a hazy band of white light, some 30° wide, arching the night sky . Although all the individual naked-eye stars in the entire sky are part of the Milky Way Galaxy, the term "Milky Way" is limited to this band of light. The light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane . Brighter regions around the band appear as soft visual patches known as star clouds . The most conspicuous of these
10089-608: The Antonines ), and the 3rd through 6th centuries. Of the Silver Age proper, Teuffel points out that anything like freedom of speech had vanished with Tiberius : ...the continual apprehension in which men lived caused a restless versatility... Simple or natural composition was considered insipid; the aim of language was to be brilliant... Hence it was dressed up with abundant tinsel of epigrams, rhetorical figures and poetical terms... Mannerism supplanted style, and bombastic pathos took
10266-571: The University of Nottingham , used 20 years of Hubble images to estimate that the observable universe contained at least two trillion ( 2 × 10 ) galaxies. However, later observations with the New Horizons space probe from outside the zodiacal light reduced this to roughly 200 billion ( 2 × 10 ). Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance
10443-486: The Very Long Baseline Array in 2009 found velocities as large as 254 km/s (570,000 mph) for stars at the outer edge of the Milky Way. Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 × 10 M ☉ within 160,000 ly (49 kpc) of its center. In 2010,
10620-478: The classici scriptores declined in the medieval period as the best form of the language yielded to medieval Latin , inferior to classical standards. The Renaissance saw a revival in Roman culture, and with it, the return of Classic ("the best") Latin. Thomas Sébillet 's Art Poétique (1548), "les bons et classiques poètes françois", refers to Jean de Meun and Alain Chartier , who the first modern application of
10797-463: The light-gathering power of this new telescope, he was able to produce astronomical photographs that resolved the outer parts of some spiral nebulae as collections of individual stars. He was also able to identify some Cepheid variables that he could use as a benchmark to estimate the distance to the nebulae. He found that the Andromeda Nebula is 275,000 parsecs from the Sun, far too distant to be part of
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#173283740907010974-594: The magnetic fields of the Milky Way were reported. The Sun is near the inner rim of the Orion Arm , within the Local Fluff of the Local Bubble , between the Radcliffe wave and Split linear structures (formerly Gould Belt ). Based upon studies of stellar orbits around Sgr A* by Gillessen et al. (2016), the Sun lies at an estimated distance of 27.14 ± 0.46 kly (8.32 ± 0.14 kpc) from
11151-437: The nebulae visible in the night sky might be separate "galaxies" themselves, similar to our own. Kant referred to both the Milky Way and the "extragalactic nebulae" as "island universes", a term still current up to the 1930s. The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of
11328-453: The observable universe . Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years ) and are separated by distances in the order of millions of parsecs (or megaparsecs). For comparison, the Milky Way has a diameter of at least 26,800 parsecs (87,400 ly) and is separated from the Andromeda Galaxy , its nearest large neighbour, by just over 750,000 parsecs (2.5 million ly). The space between galaxies
11505-466: The prima classis ("first class"), such as the authors of polished works of Latinitas , or sermo urbanus . It contains nuances of the certified and the authentic, or testis classicus ("reliable witness"). It was under this construct that Marcus Cornelius Fronto (an African - Roman lawyer and language teacher) used scriptores classici ("first-class" or "reliable authors") in the second century AD. Their works were viewed as models of good Latin. This
11682-460: The solar apex , is the direction that the Sun travels through space in the Milky Way. The general direction of the Sun's Galactic motion is towards the star Vega near the constellation of Hercules , at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun's orbit about the Milky Way is expected to be roughly elliptical with the addition of perturbations due to
11859-537: The spectra invisible to humans (radio telescopes, infrared cameras, and x-ray telescopes ) allows detection of other galaxies that are not detected by Hubble. Particularly, surveys in the Zone of Avoidance (the region of sky blocked at visible-light wavelengths by the Milky Way) have revealed a number of new galaxies. A 2016 study published in The Astrophysical Journal , led by Christopher Conselice of
12036-420: The speed of light . The Sun moves through the heliosphere at 84,000 km/h (52,000 mph). At this speed, it takes around 1,400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU ( astronomical unit ). The Solar System is headed in the direction of the zodiacal constellation Scorpius , which follows the ecliptic. A galactic quadrant, or quadrant of
12213-519: The type-cD galaxies . First described in 1964 by a paper by Thomas A. Matthews and others, they are a subtype of the more general class of D galaxies, which are giant elliptical galaxies, except that they are much larger. They are popularly known as the supergiant elliptical galaxies and constitute the largest and most luminous galaxies known. These galaxies feature a central elliptical nucleus with an extensive, faint halo of stars extending to megaparsec scales. The profile of their surface brightnesses as
12390-512: The "Great Andromeda Nebula", as the Andromeda Galaxy, Messier object M31 , was then known. Searching the photographic record, he found 11 more novae . Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within this galaxy. As a result, he was able to come up with a distance estimate of 150,000 parsecs . He became a proponent of the so-called "island universes" hypothesis, which holds that spiral nebulae are actually independent galaxies. In 1920
12567-515: The 1990s, the Hubble Space Telescope yielded improved observations. Among other things, its data helped establish that the missing dark matter in this galaxy could not consist solely of inherently faint and small stars. The Hubble Deep Field , an extremely long exposure of a relatively empty part of the sky, provided evidence that there are about 125 billion ( 1.25 × 10 ) galaxies in the observable universe. Improved technology in detecting
12744-554: The Babylonian national god , after slaying her. This story was once thought to have been based on an older Sumerian version in which Tiamat is instead slain by Enlil of Nippur , but is now thought to be purely an invention of Babylonian propagandists with the intention to show Marduk as superior to the Sumerian deities. In Greek mythology , Zeus places his son born by a mortal woman, the infant Heracles , on Hera 's breast while she
12921-458: The English translation of A History of Roman Literature gained immediate success. In 1877, Charles Thomas Cruttwell produced a similar work in English. In his preface, Cruttwell notes "Teuffel's admirable history, without which many chapters in the present work could not have attained completeness." He also credits Wagner. Cruttwell adopts the time periods found in Teuffel's work, but he presents
13098-559: The Galactic Center is about 180,000 ly (55 kpc). At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds. Hence, such objects would probably be ejected from the vicinity of the Milky Way. The integrated absolute visual magnitude of the Milky Way is estimated to be around −20.9. Both gravitational microlensing and planetary transit observations indicate that there may be at least as many planets bound to stars as there are stars in
13275-516: The Galactic Center. Boehle et al. (2016) found a smaller value of 25.64 ± 0.46 kly (7.86 ± 0.14 kpc), also using a star orbit analysis. The Sun is currently 5–30 parsecs (16–98 ly) above, or north of, the central plane of the Galactic disk. The distance between the local arm and the next arm out, the Perseus Arm , is about 2,000 parsecs (6,500 ly). The Sun, and thus
13452-422: The Galactic spiral arms and non-uniform mass distributions. In addition, the Sun passes through the Galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (damping) term. These oscillations were until recently thought to coincide with mass lifeform extinction periods on Earth. A reanalysis of the effects of the Sun's transit through
13629-421: The Golden Age. A list of canonical authors of the period whose works survived in whole or in part is shown here: The Golden Age is divided by the assassination of Julius Caesar . In the wars that followed, a generation of Republican literary figures was lost. Cicero and his contemporaries were replaced by a new generation who spent their formative years under the old constructs, and forced to make their mark under
13806-432: The Hubble classification scheme, spiral galaxies are listed as type S , followed by a letter ( a , b , or c ) which indicates the degree of tightness of the spiral arms and the size of the central bulge. An Sa galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an Sc galaxy has open, well-defined arms and a small core region. A galaxy with poorly defined arms
13983-639: The IC ( Index Catalogue ), the CGCG ( Catalogue of Galaxies and of Clusters of Galaxies ), the MCG ( Morphological Catalogue of Galaxies ), the UGC ( Uppsala General Catalogue of Galaxies), and the PGC ( Catalogue of Principal Galaxies , also known as LEDA). All the well-known galaxies appear in one or more of these catalogues but each time under a different number. For example, Messier 109 (or "M109")
14160-584: The Imperial Period, and is divided into die Zeit der julischen Dynastie ( 14–68); die Zeit der flavischen Dynastie (69–96), and die Zeit des Nerva und Trajan (96–117). Subsequently, Teuffel goes over to a century scheme: 2nd, 3rd, etc., through 6th. His later editions (which came about towards the end of the 19th century) divide the Imperial Age into parts: 1st century (Silver Age), 2nd century (the Hadrian and
14337-598: The Large Magellanic Cloud in his Book of Fixed Stars , referring to "Al Bakr of the southern Arabs", since at a declination of about 70° south it was not visible where he lived. It was not well known to Europeans until Magellan 's voyage in the 16th century. The Andromeda Galaxy was later independently noted by Simon Marius in 1612. In 1734, philosopher Emanuel Swedenborg in his Principia speculated that there might be other galaxies outside that were formed into galactic clusters that were minuscule parts of
14514-574: The Latin used in different periods deviated from "Classical" Latin, efforts were periodically made to relearn and reapply the models of the Classical period, for instance by Alcuin during the reign of Charlemagne , and later during the Renaissance , producing the highly classicising form of Latin now known as Neo-Latin . "Good Latin" in philology is known as "classical" Latin literature . The term refers to
14691-522: The Local Group and the Virgo Supercluster are contained in a much larger cosmic structure named Laniakea . The word galaxy was borrowed via French and Medieval Latin from the Greek term for the Milky Way, galaxías (kúklos) γαλαξίας ( κύκλος ) 'milky (circle)', named after its appearance as a milky band of light in the sky. In Greek mythology , Zeus places his son, born by
14868-518: The Milky Way contained all the stars in the Universe . Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis , observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. In the Babylonian epic poem Enūma Eliš , the Milky Way is created from the severed tail of the primeval salt water dragoness Tiamat , set in the sky by Marduk ,
15045-489: The Milky Way galaxy emerged. A few galaxies outside the Milky Way are visible on a dark night to the unaided eye , including the Andromeda Galaxy , Large Magellanic Cloud , Small Magellanic Cloud , and the Triangulum Galaxy . In the 10th century, Persian astronomer Abd al-Rahman al-Sufi made the earliest recorded identification of the Andromeda Galaxy, describing it as a "small cloud". In 964, he probably mentioned
15222-401: The Milky Way is "a myriad of tiny stars packed together in the sphere of the fixed stars". Proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. Galileo also concluded that the appearance of the Milky Way was due to refraction of the Earth's atmosphere. In
15399-487: The Milky Way is a barred spiral galaxy , rather than an ordinary spiral galaxy , in the 1960s. These conjectures were confirmed by the Spitzer Space Telescope observations in 2005 that showed the Milky Way's central bar to be larger than previously thought. Galaxy A galaxy is a system of stars , stellar remnants , interstellar gas , dust , and dark matter bound together by gravity . The word
15576-448: The Milky Way is the glow of stars not directly visible due to Earth's shadow, while other stars receive their light from the Sun, but have their glow obscured by solar rays. Aristotle himself believed that the Milky Way was part of the Earth's upper atmosphere, along with the stars, and that it was a byproduct of stars burning that did not dissipate because of its outermost location in the atmosphere, composing its great circle . He said that
15753-457: The Milky Way might consist of distant stars. Aristotle (384–322 BCE), however, believed the Milky Way was caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere , in the region of the World that is continuous with the heavenly motions ." Neoplatonist philosopher Olympiodorus
15930-424: The Milky Way seems to be dark matter , an unknown and invisible form of matter that interacts gravitationally with ordinary matter. A dark matter halo is conjectured to spread out relatively uniformly to a distance beyond one hundred kiloparsecs (kpc) from the Galactic Center. Mathematical models of the Milky Way suggest that the mass of dark matter is 1–1.5 × 10 M ☉ . 2013 and 2014 studies indicate
16107-431: The Milky Way was a flattened disk of stars, and that some of the nebulae visible in the night sky might be separate Milky Ways. Toward the end of the 18th century, Charles Messier compiled a catalog containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae. In 1845, Lord Rosse examined the nebulae catalogued by Herschel and observed
16284-403: The Milky Way". Viewing from the north galactic pole with 0° (zero degrees) as the ray that runs starting from the Sun and through the Galactic Center, the quadrants are: with the galactic longitude (ℓ) increasing in the counter-clockwise direction ( positive rotation ) as viewed from north of the Galactic Center (a view-point several hundred thousand light-years distant from Earth in
16461-508: The Milky Way's galactic plane occupies an area of the sky that includes 30 constellations . The Galactic Center lies in the direction of Sagittarius , where the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga . The band then continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two roughly equal hemispheres . The galactic plane
16638-521: The Milky Way, and microlensing measurements indicate that there are more rogue planets not bound to host stars than there are stars. The Milky Way contains an average of at least one planet per star, resulting in 100–400 billion planets, according to a January 2013 study of the five-planet star system Kepler-32 by the Kepler space observatory. A different January 2013 analysis of Kepler data estimated that at least 17 billion Earth-sized exoplanets reside in
16815-413: The Milky Way, refers to one of four circular sectors in the division of the Milky Way. In astronomical practice, the delineation of the galactic quadrants is based upon the galactic coordinate system , which places the Sun as the origin of the mapping system . Quadrants are described using ordinals – for example, "1st galactic quadrant", "second galactic quadrant", or "third quadrant of
16992-481: The Milky Way. Despite the prominence of large elliptical and spiral galaxies, most galaxies are dwarf galaxies. They are relatively small when compared with other galactic formations, being about one hundredth the size of the Milky Way, with only a few billion stars. Blue compact dwarf galaxies contains large clusters of young, hot, massive stars . Ultra-compact dwarf galaxies have been discovered that are only 100 parsecs across. Many dwarf galaxies may orbit
17169-432: The Milky Way. In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest exoplanet may be 4.2 light-years away, orbiting the red dwarf Proxima Centauri , according to
17346-434: The Milky Way. The ESA spacecraft Gaia provides distance estimates by determining the parallax of a billion stars and is mapping the Milky Way with four planned releases of maps in 2016, 2018, 2021 and 2024. Data from Gaia has been described as "transformational". It has been estimated that Gaia has expanded the number of observations of stars from about 2 million stars as of the 1990s to 2 billion. It has expanded
17523-402: The Milky Way. In 1926 Hubble produced a classification of galactic morphology that is used to this day. Advances in astronomy have always been driven by technology. After centuries of success in optical astronomy , infrared astronomy was attempted in the 1830s, but only blossomed in the early 1900s. Radio astronomy was born in the 1930s, and matured by the 1950s and 1960s. The problem
17700-486: The Roman Empire . Once again, Cruttwell evidences some unease with his stock pronouncements: "The Natural History of Pliny shows how much remained to be done in fields of great interest." The idea of Pliny as a model is not consistent with any sort of decline. Moreover, Pliny did his best work under emperors who were as tolerant as Augustus had been. To include some of the best writings of the Silver Age, Cruttwell extended
17877-467: The Second Period in his major work, das goldene Zeitalter der römischen Literatur ( Golden Age of Roman Literature ), dated 671–767 AUC (83 BC – AD 14), according to his own recollection. The timeframe is marked by the dictatorship of Lucius Cornelius Sulla Felix and the death of the emperor Augustus . Wagner's translation of Teuffel's writing is as follows: The golden age of the Roman literature
18054-499: The Solar System, is located in the Milky Way's galactic habitable zone . There are about 208 stars brighter than absolute magnitude 8.5 within a sphere with a radius of 15 parsecs (49 ly) from the Sun, giving a density of one star per 69 cubic parsecs, or one star per 2,360 cubic light-years (from List of nearest bright stars ). On the other hand, there are 64 known stars (of any magnitude, not counting 4 brown dwarfs ) within 5 parsecs (16 ly) of
18231-427: The Sun was undertaken by William Herschel in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the Solar System close to the center . Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on
18408-411: The Sun, giving a density of about one star per 8.2 cubic parsecs, or one per 284 cubic light-years (from List of nearest stars ). This illustrates the fact that there are far more faint stars than bright stars: in the entire sky, there are about 500 stars brighter than apparent magnitude 4 but 15.5 million stars brighter than apparent magnitude 14. The apex of the Sun's way, or
18585-497: The Younger ( c. 495 –570 CE) was critical of this view, arguing that if the Milky Way was sublunary (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have parallax , which it did not. In his view, the Milky Way was celestial. According to Mohani Mohamed, Arabian astronomer Ibn al-Haytham (965–1037) made
18762-407: The active jets emitted from active nuclei. Ultraviolet and X-ray telescopes can observe highly energetic galactic phenomena. Ultraviolet flares are sometimes observed when a star in a distant galaxy is torn apart from the tidal forces of a nearby black hole. The distribution of hot gas in galactic clusters can be mapped by X-rays. The existence of supermassive black holes at the cores of galaxies
18939-430: The advance would be perceptible by us." In time, some of Cruttwell's ideas become established in Latin philology. While praising the application of rules to classical Latin (most intensely in the Golden Age, he says "In gaining accuracy, however, classical Latin suffered a grievous loss. It became cultivated as distinct from a natural language... Spontaneity, therefore, became impossible and soon invention also ceased... In
19116-399: The ancient definition, and some of the very best writing of any period in world history was deemed stilted, degenerate, unnatural language. The Silver Age furnishes the only two extant Latin novels: Apuleius's The Golden Ass and Petronius's Satyricon . Writers of the Silver Age include: Of the additional century granted by Cruttwell to Silver Latin, Teuffel says: "The second century
19293-488: The canonical relevance of literary works written in Latin in the late Roman Republic , and early to middle Roman Empire . "[T]hat is to say, that of belonging to an exclusive group of authors (or works) that were considered to be emblematic of a certain genre." The term classicus (masculine plural classici ) was devised by the Romans to translate Greek ἐγκριθέντες (encrithentes), and "select" which refers to authors who wrote in
19470-412: The cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the centre. Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane ; but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters , the present picture of
19647-477: The center of the Milky Way. Beyond a radius of roughly 40,000 light years (13 kpc) from the center, the number of stars per cubic parsec drops much faster with radius. Surrounding the galactic disk is a spherical galactic halo of stars and globular clusters that extends farther outward, but is limited in size by the orbits of two Milky Way satellites, the Large and Small Magellanic Clouds , whose closest approach to
19824-749: The central mass is approximately 10 million solar masses , regardless of whether it has thousands or millions of stars. This suggests that galaxies are largely formed by dark matter , and that the minimum size may indicate a form of warm dark matter incapable of gravitational coalescence on a smaller scale. Interactions between galaxies are relatively frequent, and they can play an important role in galactic evolution . Near misses between galaxies result in warping distortions due to tidal interactions , and may cause some exchange of gas and dust. Collisions occur when two galaxies pass directly through each other and have sufficient relative momentum not to merge. The stars of interacting galaxies usually do not collide, but
20001-442: The core, or else due to a tidal interaction with another galaxy. Many barred spiral galaxies are active, possibly as a result of gas being channeled into the core along the arms. Our own galaxy, the Milky Way , is a large disk-shaped barred-spiral galaxy about 30 kiloparsecs in diameter and a kiloparsec thick. It contains about two hundred billion (2×10 ) stars and has a total mass of about six hundred billion (6×10 ) times
20178-399: The core, then merges into the spiral arm structure. In the Hubble classification scheme, these are designated by an SB , followed by a lower-case letter ( a , b or c ) which indicates the form of the spiral arms (in the same manner as the categorization of normal spiral galaxies). Bars are thought to be temporary structures that can occur as a result of a density wave radiating outward from
20355-470: The death of Augustus. The Ciceronian Age is further divided by the consulship of Cicero in 691 AUC (63 BC) into a first and second half. Authors are assigned to these periods by years of principal achievements. The Golden Age had already made an appearance in German philology, but in a less systematic way. In a translation of Bielfeld's Elements of universal erudition (1770): The Second Age of Latin began about
20532-469: The diameters of their host galaxies. Classical Latin Classical Latin is the form of Literary Latin recognized as a literary standard by writers of the late Roman Republic and early Roman Empire . It formed parallel to Vulgar Latin around 75 BC out of Old Latin , and developed by the 3rd century AD into Late Latin . In some later periods, the former was regarded as good or proper Latin;
20709-412: The direction of the constellation Coma Berenices ); if viewed from south of the Galactic Center (a view-point similarly distant in the constellation Sculptor ), ℓ would increase in the clockwise direction ( negative rotation ). The Milky Way is one of the two largest galaxies in the Local Group (the other being the Andromeda Galaxy ), although the size for its galactic disc and how much it defines
20886-443: The extinction of freedom... Hence arose a declamatory tone, which strove by frigid and almost hysterical exaggeration to make up for the healthy stimulus afforded by daily contact with affairs. The vein of artificial rhetoric, antithesis and epigram... owes its origin to this forced contentment with an uncongenial sphere. With the decay of freedom, taste sank... In Cruttwell's view (which had not been expressed by Teuffel), Silver Latin
21063-424: The first attempt at observing and measuring the Milky Way's parallax, and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere." Persian astronomer al-Biruni (973–1048) proposed the Milky Way galaxy was "a collection of countless fragments of the nature of nebulous stars." Andalusian astronomer Avempace ( d. 1138) proposed that it
21240-400: The formation of fossil groups or fossil clusters, where a large, relatively isolated, supergiant elliptical resides in the middle of the cluster and are surrounded by an extensive cloud of X-rays as the residue of these galactic collisions. Another older model posits the phenomenon of cooling flow , where the heated gases in clusters collapses towards their centers as they cool, forming stars in
21417-422: The fundamental characteristics of a language. The latter provides unity, allowing it to be referred to by a single name. Thus Old Latin, Classical Latin, Vulgar Latin , etc., are not considered different languages, but are all referred to by the term, Latin . This is an ancient practice continued by moderns rather than a philological innovation of recent times. That Latin had case endings is a fundamental feature of
21594-566: The galaxies' original morphology. If one of the galaxies is much more massive than the other, the result is known as cannibalism , where the more massive larger galaxy remains relatively undisturbed, and the smaller one is torn apart. The Milky Way galaxy is currently in the process of cannibalizing the Sagittarius Dwarf Elliptical Galaxy and the Canis Major Dwarf Galaxy . Stars are created within galaxies from
21771-448: The gas and dust within the two forms interacts, sometimes triggering star formation. A collision can severely distort the galaxies' shapes, forming bars, rings or tail-like structures. At the extreme of interactions are galactic mergers, where the galaxies' relative momentums are insufficient to allow them to pass through each other. Instead, they gradually merge to form a single, larger galaxy. Mergers can result in significant changes to
21948-471: The higher register that they called latinitas , sometimes translated as "Latinity". Latinitas was also called sermo familiaris ("speech of the good families"), sermo urbanus ("speech of the city"), and in rare cases sermo nobilis ("noble speech"). Besides the noun Latinitas , it was referred to with the adverb latine ("in (good) Latin", literally "Latinly") or its comparative latinius ("in better Latin", literally "more Latinly"). Latinitas
22125-470: The higher density. (The velocity returns to normal after the stars depart on the other side of the arm.) This effect is akin to a "wave" of slowdowns moving along a highway full of moving cars. The arms are visible because the high density facilitates star formation, and therefore they harbor many bright and young stars. A majority of spiral galaxies, including the Milky Way galaxy, have a linear, bar-shaped band of stars that extends outward to either side of
22302-564: The highest excellence in prose and poetry." The Ciceronian Age (known today as the "Republican Period") is dated 80–42 BC, marked by the Battle of Philippi . Cruttwell omits the first half of Teuffel's Ciceronian, and starts the Golden Age at Cicero's consulship in 63 BC—an error perpetuated in Cruttwell's second edition. He likely meant 80 BC, as he includes Varro in Golden Latin. Teuffel's Augustan Age
22479-405: The hydrogen found in the atomic form and the remaining one-third as molecular hydrogen . The mass of the Milky Way's interstellar gas is equal to between 10% and 15% of the total mass of its stars. Interstellar dust accounts for an additional 1% of the total mass of the gas. In March 2019, astronomers reported that the virial mass of the Milky Way Galaxy is 1.54 trillion solar masses within
22656-433: The isophotal diameter is not well understood. It is estimated that the significant bulk of stars in the galaxy lies within the 26 kiloparsecs (80,000 light-years) diameter, and that the number of stars beyond the outermost disc dramatically reduces to a very low number, with respect to an extrapolation of the exponential disk with the scale length of the inner disc. There are several methods being used in astronomy in defining
22833-457: The language "is marked by immaturity of art and language, by a vigorous but ill-disciplined imitation of Greek poetical models, and in prose by a dry sententiousness of style, gradually giving way to a clear and fluent strength..." These abstracts have little meaning to those not well-versed in Latin literature. In fact, Cruttwell admits "The ancients, indeed, saw a difference between Ennius , Pacuvius , and Accius , but it may be questioned whether
23010-511: The language. Whether a given form of speech prefers to use prepositions such as ad , ex , de, for "to", "from" and "of" rather than simple case endings is a matter of style. Latin has a large number of styles. Each and every author has a style, which typically allows his prose or poetry to be identified by experienced Latinists. Problems in comparative literature have risen out of group styles finding similarity by period, in which case one may speak of Old Latin, Silver Latin, Late Latin as styles or
23187-499: The latter as debased, degenerate, or corrupted. The word Latin is now understood by default to mean "Classical Latin"; for example, modern Latin textbooks almost exclusively teach Classical Latin. Cicero and his contemporaries of the late republic referred to the Latin language, in contrast to other languages such as Greek, as lingua latina or sermo latinus . They distinguished the common vernacular , however, as Vulgar Latin ( sermo vulgaris and sermo vulgi ), in contrast to
23364-466: The mass in a typical galaxy is in the form of dark matter , with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies. Galaxies are categorised according to their visual morphology as elliptical , spiral , or irregular . The Milky Way is an example of a spiral galaxy. It is estimated that there are between 200 billion ( 2 × 10 ) to 2 trillion galaxies in
23541-421: The mass of the Sun. Recently, researchers described galaxies called super-luminous spirals. They are very large with an upward diameter of 437,000 light-years (compared to the Milky Way's 87,400 light-year diameter). With a mass of 340 billion solar masses, they generate a significant amount of ultraviolet and mid-infrared light. They are thought to have an increased star formation rate around 30 times faster than
23718-524: The measurable volume of space by a factor of 100 in radius and a factor of 1,000 in precision. A study in 2020 concluded that Gaia detected a wobbling motion of the galaxy, which might be caused by " torques from a misalignment of the disc's rotation axis with respect to the principal axis of a non-spherical halo, or from accreted matter in the halo acquired during late infall, or from nearby, interacting satellite galaxies and their consequent tides". In April 2024, initial studies (and related maps) involving
23895-465: The milky appearance of the Milky Way Galaxy is due to the refraction of the Earth's atmosphere. The Neoplatonist philosopher Olympiodorus the Younger ( c. 495 –570 AD) criticized this view, arguing that if the Milky Way were sublunary , it should appear different at different times and places on Earth, and that it should have parallax , which it does not. In his view, the Milky Way
24072-507: The nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift . The controversy was conclusively settled by Edwin Hubble in the early 1920s using the Mount Wilson observatory 2.5 m (100 in) Hooker telescope . With
24249-400: The number of very-low-mass stars, which are difficult to detect, especially at distances of more than 300 ly (90 pc) from the Sun. As a comparison, the neighboring Andromeda Galaxy contains an estimated one trillion (10) stars. The Milky Way may contain ten billion white dwarfs , a billion neutron stars , and a hundred million stellar black holes . Filling the space between the stars
24426-426: The old population of the galactic halo. A 2020 study predicted the edge of the Milky Way's dark matter halo being around 292 ± 61 kpc (952,000 ± 199,000 ly ), which translates to a diameter of 584 ± 122 kpc (1.905 ± 0.3979 Mly ). The Milky Way's stellar disk is also estimated to be approximately up to 1.35 kpc (4,000 ly) thick. The Milky Way
24603-495: The ones in the Milky Way, and modelling the relationship to their surface brightnesses. This gave an isophotal diameter for the Milky Way at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years), by assuming that the galactic disc is well represented by an exponential disc and adopting a central surface brightness of the galaxy (μ 0 ) of 22.1 ± 0.3 B -mag/arcsec and a disk scale length ( h ) of 5.0 ± 0.5 kpc (16,300 ± 1,600 ly). This
24780-448: The other, would savour of artificial restriction rather than that of a natural classification." The contradiction remains—Terence is, and is not a classical author, depending on the context. Teuffel's definition of the "First Period" of Latin was based on inscriptions, fragments, and the literary works of the earliest known authors. Though he does use the term "Old Roman" at one point, most of these findings remain unnamed. Teuffel presents
24957-552: The period of classical Latin. The classical Romans distinguished Old Latin as prisca Latinitas and not sermo vulgaris . Each author's work in the Roman lists was considered equivalent to one in the Greek. In example, Ennius was the Latin Homer , Aeneid was the equivalent of Iliad , etc. The lists of classical authors were as far as the Roman grammarians went in developing a philology . The topic remained at that point while interest in
25134-410: The period through the death of Marcus Aurelius (180 AD). The philosophic prose of a good emperor was in no way compatible with either Teuffel's view of unnatural language, or Cruttwell's depiction of a decline. Having created these constructs, the two philologists found they could not entirely justify them. Apparently, in the worst implication of their views, there was no such thing as Classical Latin by
25311-575: The philological notion of classical Latin through a typology similar to the Ages of Man , setting out the Golden and Silver Ages of classical Latin. Wilhem Wagner, who published Teuffel's work in German, also produced an English translation which he published in 1873. Teuffel's classification, still in use today (with modifications), groups classical Latin authors into periods defined by political events rather than by style. Teuffel went on to publish other editions, but
25488-466: The photographic record, he found 11 more novae . Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within the Milky Way. As a result, he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the "island universes" hypothesis, which held that the spiral nebulae were independent galaxies. In 1920 the Great Debate took place between Harlow Shapley and Heber Curtis, concerning
25665-419: The place of quiet power. The content of new literary works was continually proscribed by the emperor, who exiled or executed existing authors and played the role of literary man, himself (typically badly). Artists therefore went into a repertory of new and dazzling mannerisms, which Teuffel calls "utter unreality." Cruttwell picks up this theme: The foremost of these [characteristics] is unreality, arising from
25842-467: The process, a phenomenon observed in clusters such as Perseus , and more recently in the Phoenix Cluster . A shell galaxy is a type of elliptical galaxy where the stars in its halo are arranged in concentric shells. About one-tenth of elliptical galaxies have a shell-like structure, which has never been observed in spiral galaxies. These structures are thought to develop when a larger galaxy absorbs
26019-401: The relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter (24.3 mm (0.955 in)), the Milky Way would be approximately at least the greatest north–south line of the contiguous United States . An even older study from 1978 gave a lower diameter for Milky Way about 23 kpc (75,000 ly). A 2015 paper discovered that there is
26196-521: The root of "galaxy", the name for our, and later all such, collections of stars. The Milky Way, or "milk circle", was just one of 11 "circles" the Greeks identified in the sky, others being the zodiac , the meridian , the horizon , the equator , the tropics of Cancer and Capricorn , the Arctic Circle and the Antarctic Circle , and two colure circles passing through both poles. The Milky Way
26373-510: The size of a galaxy, and each of them can yield different results with respect to one another. The most commonly employed method is the D 25 standard – the isophote where the photometric brightness of a galaxy in the B-band (445 nm wavelength of light, in the blue part of the visible spectrum ) reaches 25 mag/arcsec. An estimate from 1997 by Goodwin and others compared the distribution of Cepheid variable stars in 17 other spiral galaxies to
26550-439: The sources in these two types of galaxies may differ. Radio galaxies can also be classified as giant radio galaxies (GRGs), whose radio emissions can extend to scales of megaparsecs (3.26 million light-years). Alcyoneus is an FR II class low-excitation radio galaxy which has the largest observed radio emission, with lobed structures spanning 5 megaparsecs (16×10 ly ). For comparison, another similarly sized giant radio galaxy
26727-490: The south galactic pole is near α Sculptoris . Because of this high inclination, depending on the time of night and year, the Milky Way arch may appear relatively low or relatively high in the sky. For observers from latitudes approximately 65° north to 65° south, the Milky Way passes directly overhead twice a day. In Meteorologica , Aristotle (384–322 BC) states that the Greek philosophers Anaxagoras ( c. 500 –428 BC) and Democritus (460–370 BC) proposed that
26904-461: The sphere of the fixed stars." Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer Galileo Galilei used a telescope to study it and discovered it was composed of a huge number of faint stars. In 1750, English astronomer Thomas Wright , in his An Original Theory or New Hypothesis of the Universe , correctly speculated that it might be a rotating body of
27081-463: The spiral arms (more at the bulge). Recent simulations suggest that a dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years (613 kpc). The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster , which is itself a component of the Laniakea Supercluster . It
27258-460: The spiral structure based on CO data has failed to find a correlation. It takes the Solar System about 240 million years to complete one orbit of the Milky Way (a galactic year ), so the Sun is thought to have completed 18–20 orbits during its lifetime and 1/1250 of a revolution since the origin of humans . The orbital speed of the Solar System about the center of the Milky Way is approximately 220 km/s (490,000 mph) or 0.073% of
27435-568: The spiral structure of Messier object M51 , now known as the Whirlpool Galaxy. In 1912, Vesto M. Slipher made spectrographic studies of the brightest spiral nebulae to determine their composition. Slipher discovered that the spiral nebulae have high Doppler shifts , indicating that they are moving at a rate exceeding the velocity of the stars he had measured. He found that the majority of these nebulae are moving away from us. In 1917, Heber Doust Curtis observed nova S Andromedae within
27612-510: The stellar disk larger by increasing to this size. A more recent 2018 paper later somewhat ruled out this hypothesis, and supported a conclusion that the Monoceros Ring, A13 and TriAnd Ring were stellar overdensities rather kicked out from the main stellar disk, with the velocity dispersion of the RR Lyrae stars found to be higher and consistent with halo membership. Another 2018 study revealed
27789-437: The term "pre-classical" to Old Latin and implicating it to post-classical (or post-Augustan) and silver Latin, Cruttwell realized that his construct was not accordance with ancient usage and assertions: "[T]he epithet classical is by many restricted to the authors who wrote in it [golden Latin]. It is best, however, not to narrow unnecessarily the sphere of classicity; to exclude Terence on the one hand or Tacitus and Pliny on
27966-421: The time of Caesar [his ages are different from Teuffel's], and ended with Tiberius. This is what is called the Augustan Age, which was perhaps of all others the most brilliant, a period at which it should seem as if the greatest men, and the immortal authors, had met together upon the earth, in order to write the Latin language in its utmost purity and perfection... and of Tacitus, his conceits and sententious style
28143-498: The universe that extended far beyond what could be seen. These views "are remarkably close to the present-day views of the cosmos." In 1745, Pierre Louis Maupertuis conjectured that some nebula -like objects were collections of stars with unique properties, including a glow exceeding the light its stars produced on their own, and repeated Johannes Hevelius 's view that the bright spots were massive and flattened due to their rotation. In 1750, Thomas Wright correctly speculated that
28320-442: The universe's early history, but still contribute an estimated 15% to total star production. Starburst galaxies are characterized by dusty concentrations of gas and the appearance of newly formed stars, including massive stars that ionize the surrounding clouds to create H II regions . These stars produce supernova explosions, creating expanding remnants that interact powerfully with the surrounding gas. These outbursts trigger
28497-452: The universe, the Milky Way galaxy has a below average amount of neutrino luminosity making our galaxy a " neutrino desert ". The Milky Way consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. The mass distribution within the Milky Way closely resembles the type Sbc in the Hubble classification , which represents spiral galaxies with relatively loosely wound arms. Astronomers first began to conjecture that
28674-399: The very probable presence of disk stars at 26–31.5 kpc (84,800–103,000 ly) from the Galactic Center or perhaps even farther, significantly beyond approximately 13–20 kpc (40,000–70,000 ly), in which it was once believed to be the abrupt drop-off of the stellar density of the disk, meaning that few or no stars were expected to be above this limit, save for stars that belong to
28851-475: The visible sky. He produced a diagram of the shape of the Milky Way with the Solar System close to the center. In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral-shaped nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture. In 1904, studying the proper motions of stars, Jacobus Kapteyn reported that these were not random, as it
29028-549: The watchful eye of a new emperor. The demand for great orators had ceased, shifting to an emphasis on poetry. Other than the historian Livy , the most remarkable writers of the period were the poets Virgil , Horace , and Ovid . Although Augustus evidenced some toleration to republican sympathizers, he exiled Ovid, and imperial tolerance ended with the continuance of the Julio-Claudian dynasty . Augustan writers include: In his second volume, Imperial Period , Teuffel initiated
29205-693: The word universe implied the entirety of existence. Instead, they became known simply as galaxies. Millions of galaxies have been catalogued, but only a few have well-established names, such as the Andromeda Galaxy , the Magellanic Clouds , the Whirlpool Galaxy , and the Sombrero Galaxy . Astronomers work with numbers from certain catalogues, such as the Messier catalogue , the NGC ( New General Catalogue ),
29382-489: The words. According to Merriam Webster's Collegiate Dictionary , the term classical (from classicus) entered modern English in 1599, some 50 years after its re-introduction to the continent. In Governor William Bradford 's Dialogue (1648), he referred to synods of a separatist church as "classical meetings", defined by meetings between "young men" from New England and "ancient men" from Holland and England. In 1715, Laurence Echard 's Classical Geographical Dictionary
29559-442: Was a "rank, weed-grown garden," a "decline." Cruttwell had already decried what he saw as a loss of spontaneity in Golden Latin. Teuffel regarded the Silver Age as a loss of natural language, and therefore of spontaneity, implying that it was last seen in the Golden Age. Instead, Tiberius brought about a "sudden collapse of letters." The idea of a decline had been dominant in English society since Edward Gibbon 's Decline and Fall of
29736-487: Was a form of sermo (spoken language), and as such, retains spontaneity. No texts by Classical Latin authors are noted for the type of rigidity evidenced by stylized art, with the exception of repetitious abbreviations and stock phrases found on inscriptions. The standards, authors and manuals from the Classical Latin period formed the model for the language taught and used in later periods across Europe and beyond. While
29913-478: Was a happy period for the Roman State, the happiest indeed during the whole Empire... But in the world of letters the lassitude and enervation, which told of Rome's decline, became unmistakeable... its forte is in imitation." Teuffel, however, excepts the jurists; others find other "exceptions", recasting Teuffels's view. Style of language refers to repeatable features of speech that are somewhat less general than
30090-455: Was able to define sublime, intermediate, and low styles within Classical Latin. St. Augustine recommended low style for sermons. Style was to be defined by deviation in speech from a standard. Teuffel termed this standard "Golden Latin". John Edwin Sandys , who was an authority in Latin style for several decades, summarizes the differences between Golden and Silver Latin as follows: Silver Latin
30267-502: Was believed in that time; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that Kapteyn's data had been the first evidence of the rotation of our galaxy, which ultimately led to the finding of galactic rotation by Bertil Lindblad and Jan Oort . In 1917, Heber Doust Curtis had observed the nova S Andromedae within the Great Andromeda Nebula ( Messier object 31). Searching
30444-416: Was composed of many stars that almost touched one another, and appeared to be a continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars as evidence of this occurring when two objects were near. In the 14th century, Syrian-born Ibn Qayyim al-Jawziyya proposed the Milky Way galaxy was "a myriad of tiny stars packed together in
30621-405: Was confirmed through X-ray astronomy. In 1944, Hendrik van de Hulst predicted that microwave radiation with wavelength of 21 cm would be detectable from interstellar atomic hydrogen gas; and in 1951 it was observed. This radiation is not affected by dust absorption, and so its Doppler shift can be used to map the motion of the gas in this galaxy. These observations led to the hypothesis of
30798-400: Was equal to the Golden Age, his Third Period die römische Kaiserheit encompasses both the Silver Age and the centuries now termed Late Latin , in which the forms seemed to break loose from their foundation and float freely. That is, men of literature were confounded about the meaning of "good Latin." The last iteration of Classical Latin is known as Silver Latin. The Silver Age is the first of
30975-721: Was published. In 1736, Robert Ainsworth 's Thesaurus Linguae Latinae Compendarius turned English words and expressions into "proper and classical Latin." In 1768, David Ruhnken 's Critical History of the Greek Orators recast the molded view of the classical by applying the word "canon" to the pinakes of orators after the Biblical canon , or list of authentic books of the Bible. In doing so, Ruhnken had secular catechism in mind. In 1870, Wilhelm Sigismund Teuffel 's Geschichte der Römischen Literatur ( A History of Roman Literature ) defined
31152-410: Was spoken and written. It was the language taught in schools. Prescriptive rules therefore applied to it, and when special subjects like poetry or rhetoric were taken into consideration, additional rules applied. Since spoken Latinitas has become extinct (in favor of subsequent registers), the rules of politus (polished) texts may give the appearance of an artificial language. However, Latinitas
31329-493: Was that air only allows visible light and radio waves to pass, with a little bit of near infrared. The first ultraviolet telescope was launched in 1968, and since then there's been major progress in all regions of the electromagnetic spectrum . The dust present in the interstellar medium is opaque to visual light. It is more transparent to far-infrared , which can be used to observe the interior regions of giant molecular clouds and galactic cores in great detail. Infrared
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