Nova Scotia is one of Canada's three Maritime Provinces, one of the four provinces that form Atlantic Canada. Its provincial capital is Halifax. Nova Scotia is the second-smallest of Canada's ten provinces, with an area of 55,284 square kilometres, including Cape Breton and another 3,800 coastal islands; as of 2016, the population was 923,598. Nova Scotia is Canada's second-most-densely populated province, after Prince Edward Island, with 17.4 inhabitants per square kilometre. "Nova Scotia" means "New Scotland" in Latin and is the recognized English-language name for the province. In both French and Scottish Gaelic, the province is directly translated as "New Scotland". In general and Slavic languages use a direct translation of "New Scotland", while most other languages use direct transliterations of the Latin / English name; the province was first named in the 1621 Royal Charter granting to Sir William Alexander in 1632 the right to settle lands including modern Nova Scotia, Cape Breton Island, Prince Edward Island, New Brunswick and the Gaspé Peninsula.
Nova Scotia is Canada's smallest province in area after Prince Edward Island. The province's mainland is the Nova Scotia peninsula surrounded by the Atlantic Ocean, including numerous bays and estuaries. Nowhere in Nova Scotia is more than 67 km from the ocean. Cape Breton Island, a large island to the northeast of the Nova Scotia mainland, is part of the province, as is Sable Island, a small island notorious for its shipwrecks 175 km from the province's southern coast. Nova Scotia has many ancient fossil-bearing rock formations; these formations are rich on the Bay of Fundy's shores. Blue Beach near Hantsport, Joggins Fossil Cliffs, on the Bay of Fundy's shores, has yielded an abundance of Carboniferous-age fossils. Wasson's Bluff, near the town of Parrsboro, has yielded both Triassic- and Jurassic-age fossils; the province contains 5,400 lakes. Nova Scotia lies in the mid-temperate zone and, although the province is surrounded by water, the climate is closer to continental climate rather than maritime.
The winter and summer temperature extremes of the continental climate are moderated by the ocean. However, winters are cold enough to be classified as continental—still being nearer the freezing point than inland areas to the west; the Nova Scotian climate is in many ways similar to the central Baltic Sea coast in Northern Europe, only wetter and snowier. This is true in spite of Nova Scotia's being some fifteen parallels south. Areas not on the Atlantic coast experience warmer summers more typical of inland areas, winter lows a little colder. Described on the provincial vehicle licence plate as Canada's Ocean Playground, Nova Scotia is surrounded by four major bodies of water: the Gulf of Saint Lawrence to the north, the Bay of Fundy to the west, the Gulf of Maine to the southwest, Atlantic Ocean to the east; the province includes regions of the Mi'kmaq nation of Mi'kma'ki. The Mi'kmaq people inhabited Nova Scotia at the time the first European colonists arrived. In 1605, French colonists established the first permanent European settlement in the future Canada at Port Royal, founding what would become known as Acadia.
The British conquest of Acadia took place in 1710. The Treaty of Utrecht in 1713 formally recognized this and returned Cape Breton Island to the French. Present-day New Brunswick still formed a part of the French colony of Acadia. After the capture of Port Royal in 1710, Francis Nicholson announced it would be renamed Annapolis Royal in honor of Queen Anne. In 1749, the capital of Nova Scotia moved from Annapolis Royal to the newly established Halifax. In 1755 the vast majority of the French population was forcibly removed in the Expulsion of the Acadians. In 1763, most of Acadia became part of Nova Scotia. In 1769, St. John's Island became a separate colony. Nova Scotia included present-day New Brunswick until that province's establishment in 1784, after the arrival of United Empire Loyalists. In 1867, Nova Scotia became one of the four founding provinces of the Canadian Confederation; the warfare on Nova Scotian soil during the 17th and 18th centuries influenced the history of Nova Scotia. The Mi'kmaq had lived in Nova Scotia for centuries.
The French arrived in 1604, Catholic Mi'kmaq and Acadians formed the majority of the population of the colony for the next 150 years. During the first 80 years the French and Acadians lived in Nova Scotia, nine significant military clashes took place as the English and Scottish and French fought for possession of the area; these encounters happened at Port Royal, Saint John, Cap de Sable and Baleine. The Acadian Civil War took place from 1640 to 1645. Beginning with King William's War in 1688, six wars took place in Nova Scotia before the British defeated the French and made peace with the Mi'kmaq: King William's War, Queen Anne's War, Father Rale's War, King George's War, Father Le Loutre’s War The Seven Years' War called the French and Indian War The battles during these wars took place Port Royal, Saint John, Chignecto, Dartmouth and Grand-Pré. Despite the British conquest of Acadia in 1710, Nova Scotia remained occupied
A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth; the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the estimated 300 sextillion stars in the Universe are invisible to the naked eye from Earth, including all stars outside our galaxy, the Milky Way. For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and radiates into outer space. All occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime, for some stars by supernova nucleosynthesis when it explodes.
Near the end of its life, a star can contain degenerate matter. Astronomers can determine the mass, age and many other properties of a star by observing its motion through space, its luminosity, spectrum respectively; the total mass of a star is the main factor. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined. A star's life begins with the gravitational collapse of a gaseous nebula of material composed of hydrogen, along with helium and trace amounts of heavier elements; when the stellar core is sufficiently dense, hydrogen becomes converted into helium through nuclear fusion, releasing energy in the process. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective heat transfer processes.
The star's internal pressure prevents it from collapsing further under its own gravity. A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements in shells around the core; as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled as new stars. Meanwhile, the core becomes a stellar remnant: a white dwarf, a neutron star, or if it is sufficiently massive a black hole. Binary and multi-star systems consist of two or more stars that are gravitationally bound and move around each other in stable orbits; when two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy. Stars have been important to civilizations throughout the world, they have used for celestial navigation and orientation.
Many ancient astronomers believed that stars were permanently affixed to a heavenly sphere and that they were immutable. By convention, astronomers grouped stars into constellations and used them to track the motions of the planets and the inferred position of the Sun; the motion of the Sun against the background stars was used to create calendars, which could be used to regulate agricultural practices. The Gregorian calendar used nearly everywhere in the world, is a solar calendar based on the angle of the Earth's rotational axis relative to its local star, the Sun; the oldest dated star chart was the result of ancient Egyptian astronomy in 1534 BC. The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period; the first star catalogue in Greek astronomy was created by Aristillus in 300 BC, with the help of Timocharis. The star catalog of Hipparchus included 1020 stars, was used to assemble Ptolemy's star catalogue.
Hipparchus is known for the discovery of the first recorded nova. Many of the constellations and star names in use today derive from Greek astronomy. In spite of the apparent immutability of the heavens, Chinese astronomers were aware that new stars could appear. In 185 AD, they were the first to observe and write about a supernova, now known as the SN 185; the brightest stellar event in recorded history was the SN 1006 supernova, observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers. The SN 1054 supernova, which gave birth to the Crab Nebula, was observed by Chinese and Islamic astronomers. Medieval Islamic astronomers gave Arabic names to many stars that are still used today and they invented numerous astronomical instruments that could compute the positions of the stars, they built the first large observatory research institutes for the purpose of producing Zij star catalogues. Among these, the Book of Fixed Stars was written by the Persian astronomer Abd al-Rahman al-Sufi, who observed a number of stars, star clusters and galaxies.
According to A. Zahoor, in the 11th century, the Persian polymath scholar Abu Rayhan Biruni described the Milky
New Brunswick is one of four Atlantic provinces on the east coast of Canada. According to the Constitution of Canada, New Brunswick is the only bilingual province. About two thirds of the population declare themselves a third francophones. One third of the population describes themselves as bilingual. Atypically for Canada, only about half of the population lives in urban areas in Greater Moncton, Greater Saint John and the capital Fredericton. Unlike the other Maritime provinces, New Brunswick's terrain is forested uplands, with much of the land further from the coast, giving it a harsher climate. New Brunswick is 83% forested, less densely-populated than the rest of the Maritimes. Being close to Europe, New Brunswick was among the first places in North America to be explored and settled by Europeans, starting with the French in the early 1600s, who displaced the indigenous Mi'kmaq and the Passamaquoddy peoples; the French settlers were displaced when the area became part of the British Empire.
In 1784, after an influx of refugees from the American Revolutionary War, the province was partitioned from Nova Scotia. The province prospered in the early 1800s and the population grew reaching about a quarter of a million by mid-century. In 1867, New Brunswick was one of four founding provinces of the Canadian Confederation, along with Nova Scotia and the Province of Canada. After Confederation, wooden shipbuilding and lumbering declined, while protectionism disrupted trade ties with New England; the mid-1900s found New Brunswick to be one of the poorest regions of Canada, now mitigated by Canadian transfer payments and improved support for rural areas. As of 2002, provincial gross domestic product was derived as follows: services 43%. Tourism accounts for about 9 % of the labour force indirectly. Popular destinations include Fundy National Park and the Hopewell Rocks, Kouchibouguac National Park, Roosevelt Campobello International Park. In 2013, 64 cruise ships called at Port of Saint John carrying on average 2600 passengers each.
Indigenous peoples have been in the area since about 7000 BC. At the time of European contact, inhabitants were the Mi'kmaq, the Maliseet, the Passamaquoddy. Although these tribes did not leave a written record, their language is present in many placenames, such as Aroostook, Petitcodiac and Shediac. New Brunswick may have been part of Vinland during the Norse exploration of North America, Basque and Norman fishermen may have visited the Bay of Fundy in the early 1500s; the first documented European visits were by Jacques Cartier in 1534. In 1604, a party including Samuel de Champlain visited the mouth of the Saint John River on the eponymous Saint-Jean-Baptiste Day. Now Saint John, this was the site of the first permanent European settlement in New Brunswick. French settlement extended up the river to the site of present-day Fredericton. Other settlements in the southeast extended from Beaubassin, near the present-day border with Nova Scotia, to Baie Verte, up the Petitcodiac and Shepody Rivers.
By the early 1700s the area was part of the French colony of Acadia, in turn part of New France. Acadia covered what is now the Maritimes, as well as bits of Maine. In the early 1700s, rivalry between Britain and France for control of territory led to the 1713 Treaty of Utrecht, under which Acadia was reduced to Île Saint-Jean and Île-Royale; the ownership of New Brunswick being disputed, with an informal border on the Isthmus of Chignecto. The British prevailed, leading to the 1755 Expulsion of the Acadians. Present-day New Brunswick became part of the colony of Nova Scotia. Hostilities ended with the Treaty of Paris in 1763, Acadians returning from exile discovered several thousand immigrants from New England, on their former lands; some settled along the Saint John River. Settlement was slow. Pennsylvanian immigrants founded Moncton in 1766, English settlers from Yorkshire arrived in the Sackville area. After the American Revolution, about 10,000 loyalist refugees settled along the north shore of the Bay of Fundy, commemorated in the province's motto, Spem reduxit.
The number reached 14,000 by 1784, with about one in ten returning to America. The same year New Brunswick was partitioned from Nova Scotia and that year saw its first elected assembly; the colony was named New Brunswick in honour of George III, King of Great Britain, King of Ireland, Prince-elector of Brunswick-Lüneburg in what is now Germany. In 1785 Saint John became Canada's first incorporated city; the population of the colony reached 26,000 in 1806 and 35,000 in 1812. The 1800s saw an age of prosperity based on wood export and shipbuilding, bolstered by The Canadian–American Reciprocity Treaty of 1854 and demand from the American Civil War. St. Martins became the third most productive shipbuilding town in the Maritimes, producing over 500 vessels; the first half of the 1800s saw large-scale immigration from Ireland and Scotland, with the population reaching 252,047 by 1861. In 1848, responsible home government was granted and the 1850s saw the emergence of political parties organised along religious and ethnic lines.
The notion of unifying the separate colonies of British North America was discussed i
Psi¹ Draconis designated 31 Draconis, is a triple star system in the northern constellation of Draco. The system is close, is located about 75 light-years from the Sun, based on its parallax. Psi¹ Draconis was considered a binary star consisting of a F-type subgiant and a F-type main-sequence star, designated Psi¹ Draconis A and Psi¹ Draconis B, respectively. In 2015, Psi¹ Draconis A was itself found to be a double-lined spectroscopic binary, making the system a triple; the companion to Psi¹ Draconis A was designated Psi¹ Draconis C by its discoverers. In 2015, Psi¹ Draconis B was discovered to be orbited by an exoplanet, designated Psi¹ Draconis Bb. Ψ ¹ Draconis is 31 Draconis its Flamsteed designation. The designation of the components – ψ¹ Draconis A and B – derives from the convention used by the Washington Multiplicity Catalog for multiple star systems, adopted by the International Astronomical Union. Psi¹ Draconis bore the traditional name of Dziban or Dsiban, derived from the Arabic Adh-Dhi'ban, meaning "The two wolves" or "The two jackals".
In 2016, the IAU organized a Working Group on Star Names to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems, it approved the name Dziban for the component Psi¹ Draconis A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names. In Chinese astronomy, Psi¹ Draconis is called 女史, Pinyin: Nǚshǐ, meaning Female Protocol, because this star is marking itself and stands alone in the asterism Female Protocol in the Purple Forbidden enclosure. 女史 has been Latinised into Niu She by R. H. Allen, meaning "the Palace Governess", or "a Literary Woman". Ψ¹ Draconis AC and ψ¹ Draconis B are separated by about 31 arcseconds. Only a small fraction of the orbit has been observed: an orbit of with a period 10,000 years has been calculated, but it is preliminary and to be in high error. Ψ¹ Draconis A and C have varying radial velocities in respect to Earth, indicating that there must be orbital motion.
The orbital period is estimated to be around 20 years, the eccentricity must be high, around 0.679. Psi ¹ Draconis Bb is a Jupiter-like exoplanet orbiting the secondary star; the planet was discovered when periodic Doppler shifts in the star's spectrum revealed the presence of a planet, similar to the spectroscopic binary nature of Psi¹ Draconis AC. Its minimum mass is 1.53 MJ, it orbits its host star every 8.5 years taking a eccentric orbit
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, moons and galaxies – in either observational or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology. Astronomers fall under either of two main types: observational and theoretical. Observational astronomers analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed; because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form and die. They use these data to create models or simulations to theorize how different celestial objects work.
Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology. Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws. Today, that distinction has disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are educated individuals who have a Ph. D. in physics or astronomy and are employed by research institutions or universities. They spend the majority of their time working on research, although they quite have other duties such as teaching, building instruments, or aiding in the operation of an observatory; the number of professional astronomers in the United States is quite small. The American Astronomical Society, the major organization of professional astronomers in North America, has 7,000 members; this number includes scientists from other fields such as physics and engineering, whose research interests are related to astronomy.
The International Astronomical Union comprises 10,145 members from 70 different countries who are involved in astronomical research at the Ph. D. beyond. Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend little time at telescopes just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field.
Those who become astronomers have a broad background in maths and computing in high school. Taking courses that teach how to research and present papers are invaluable. In college/university most astronomers get a Ph. D. in astronomy or physics. While there is a low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and host star parties; the Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research.
List of astronomers List of women astronomers List of Muslim astronomers List of French astronomers List of Hungarian astronomers List of Russian astronomers and astrophysicists List of Slovenian astronomers Dallal, Ahmad. "Science and Technology". In Esposito, John; the Oxford History of Islam. Oxford University Press, New York. ISBN 0-300-15911-0. Kennedy, E. S.. "A Survey of Islamic Astronomical Tables. 46. Philadelphia: American Philosophical Society. Toomer, Gerald. "Al-Khwārizmī, Abu Jaʿfar Muḥammad ibn Mūsā". In Gillispie, Charles Coulston. Dictionary of Scientific Biography. 7. New York: Charles Scribner's Sons. ISBN 0-684-16962-2. American Astronomical Society European Astronomical Society International Astronomical Union Astronomical Society of the Pacific Space's astronomy news
A supernova is an event that occurs upon the death of certain types of stars. Supernovae are more energetic than novae. In Latin, nova means "new", referring astronomically to what appears to be a temporary new bright star. Adding the prefix "super-" distinguishes supernovae from ordinary novae, which are far less luminous; the word supernova was coined by Walter Baade and Fritz Zwicky in 1931. Only three Milky Way, naked-eye supernova events have been observed during the last thousand years, though many have been seen in other galaxies; the most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604, but two more recent supernova remnants have been found. Statistical observations of supernovae in other galaxies suggest they occur on average about three times every century in the Milky Way, that any galactic supernova would certainly be observable with modern astronomical telescopes. Supernovae may expel much, if not all, of the material away from a star at velocities up to 30,000 km/s or 10% of the speed of light.
This drives an expanding and fast-moving shock wave into the surrounding interstellar medium, in turn, sweeping up an expanding shell of gas and dust, observed as a supernova remnant. Supernovae create and eject the bulk of the chemical elements produced by nucleosynthesis. Supernovae play a significant role in enriching the interstellar medium with the heavier atomic mass chemical elements. Furthermore, the expanding shock waves from supernovae can trigger the formation of new stars. Supernova remnants are expected to accelerate a large fraction of galactic primary cosmic rays, but direct evidence for cosmic ray production was found only in a few of them so far, they are potentially strong galactic sources of gravitational waves. Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first instance, a degenerate white dwarf may accumulate sufficient material from a binary companion, either through accretion or via a merger, to raise its core temperature enough to trigger runaway nuclear fusion disrupting the star.
In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time. Owing to the wide range of astrophysical consequences of these events, astronomers now deem supernova research, across the fields of stellar and galactic evolution, as an important area for investigation; the earliest recorded supernova HB9 was viewed by Indians 5,000-years ago and recorded in the oldest Star chart. The SN 185, was viewed by Chinese astronomers in 185 AD; the brightest recorded supernova was SN 1006, which occurred in 1006 AD and was described by observers across China, Iraq and Europe. The observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the latest to be observed with the naked eye in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was static and unchanging.
Johannes Kepler began observing SN 1604 at its peak on October 17, 1604, continued to make estimates of its brightness until it faded from naked eye view a year later. It was the second supernova to be observed in a generation. There is some evidence that the youngest galactic supernova, G1.9+0.3, occurred in the late 19th century more than Cassiopeia A from around 1680. Neither supernova was noted at the time. In the case of G1.9+0.3, high extinction along the plane of the galaxy could have dimmed the event sufficiently to go unnoticed. The situation for Cassiopeia A is less clear. Infrared light echos have been detected showing that it was a type IIb supernova and was not in a region of high extinction. Before the development of the telescope, only five supernovae were seen in the last millennium. Compared to a star's entire history, the visual appearance of a galactic supernova is brief spanning several months, so that the chances of observing one is once in a lifetime. Only a tiny fraction of the 100 billion stars in a typical galaxy have the capacity to become a supernova, restricted to either those having large mass or extraordinarily rare kinds of binary stars containing white dwarfs.
However and discovery of extragalactic supernovae are now far more common. The first such observation was of SN 1885A in the Andromeda galaxy. Today and professional astronomers are finding several hundred every year, some when near maximum brightness, others on old astronomical photographs or plates. American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941. During the 1960s, astronomers found that the maximum intensities of supernovae could be used as standard candles, hence indicators of astronomical distances; some of the most distant supernovae observed in 2003, appeared dimmer than expected. This supports the view. Techniques were developed for reconstructing supernovae events that have no written records of being observed; the date of the Cassiopeia A supernova event was determined from light echoes off nebulae, while the age of supernova remnant RX J0852.0-4622 was estimated from temperature
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines; each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary due to the temperature of the photosphere, although in some cases there are true abundance differences; the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are classified under the Morgan-Keenan system using the letters O, B, A, F, G, K, M, a sequence from the hottest to the coolest; each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and classes S and C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd for sub-dwarfs, class D for white dwarfs; the full spectral class for the Sun is G2V, indicating a main-sequence star with a temperature around 5,800 K. The conventional color description takes into account only the peak of the stellar spectrum. In actuality, stars radiate in all parts of the spectrum; because all spectral colors combined appear white, the actual apparent colors the human eye would observe are far lighter than the conventional color descriptions would suggest. This characteristic of'lightness' indicates that the simplified assignment of colors within the spectrum can be misleading.
Excluding color-contrast illusions in dim light, there are indigo, or violet stars. Red dwarfs are a deep shade of orange, brown dwarfs do not appear brown, but hypothetically would appear dim grey to a nearby observer; the modern classification system is known as the Morgan–Keenan classification. Each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the star's spectral type. Other modern stellar classification systems, such as the UBV system, are based on color indexes—the measured differences in three or more color magnitudes; those numbers are given labels such as "U-V" or "B-V", which represent the colors passed by two standard filters. The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon, who re-ordered and simplified a prior alphabetical system. Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions.
Main-sequence stars vary in surface temperature from 2,000 to 50,000 K, whereas more-evolved stars can have temperatures above 100,000 K. Physically, the classes indicate the temperature of the star's atmosphere and are listed from hottest to coldest; the spectral classes O through M, as well as other more specialized classes discussed are subdivided by Arabic numerals, where 0 denotes the hottest stars of a given class. For example, A0 denotes A9 denotes the coolest ones. Fractional numbers are allowed; the Sun is classified as G2. Conventional color descriptions are traditional in astronomy, represent colors relative to the mean color of an A class star, considered to be white; the apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, appear white or bluish white to the unaided eye because they are too dim for color vision to work. Red supergiants are cooler and redder than dwarfs of the same spectral type, stars with particular spectral features such as carbon stars may be far redder than any black body.
The fact that the Harvard classification of a star indicated its surface or photospheric temperature was not understood until after its development, though by the time the first Hertzsprung–Russell diagram was formulated, this was suspected to be true. In the 1920s, the Indian physicist Meghnad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First he applied it to the solar chromosphere to stellar spectra. Harvard astronomer Cecilia Payne demonstrated that the O-B-A-F-G-K-M spectral sequence is a sequence in temperature; because the classification sequence predates our understanding that it is a temperature sequence, the placement of a spectrum into a given subtype, such as B3 or A7, depends upon estimates of the strengths of absorption features in stellar spectra. As a result, these subtypes are not evenly divided into any sort of mathematically representable intervals; the Yerkes spectral classification called the MKK system from the authors' initial