International Astronomical Union
The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the internationally recognized authority for assigning designations and names to celestial bodies and any surface features on them; the IAU is a member of the International Council for Science. Its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation; the IAU maintains friendly relations with organizations that include amateur astronomers in their membership. The IAU has its head office on the second floor of the Institut d'Astrophysique de Paris in the 14th arrondissement of Paris. Working groups include the Working Group for Planetary System Nomenclature, which maintains the astronomical naming conventions and planetary nomenclature for planetary bodies, the Working Group on Star Names, which catalogs and standardizes proper names for stars.
The IAU is responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams. The Minor Planet Center operates under the IAU, is a "clearinghouse" for all non-planetary or non-moon bodies in the Solar System; the Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers. The IAU was founded on 28 July 1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. Two subsidiaries of the IAU were created at this assembly: the International Time Commission seated at the International Time Bureau in Paris and the International Central Bureau of Astronomical Telegrams seated in Copenhagen, Denmark; the 7 initial member states were Belgium, France, Great Britain, Greece and the United States, soon to be followed by Italy and Mexico. The first executive committee consisted of Benjamin Baillaud, Alfred Fowler, four vice presidents: William Campbell, Frank Dyson, Georges Lecointe, Annibale Riccò.
Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets. The reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, 2–10 May 1922. By the end of the first General Assembly, ten additional nations had joined the Union, bringing the total membership to 19 countries. Although the Union was formed eight months after the end of World War I, international collaboration in astronomy had been strong in the pre-war era; the first 50 years of the Union's history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents and General Secretaries. Twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Union's history in IAU Information Bulletin No. 100. Six past IAU Presidents in the period 1976–2003 contributed their recollections in IAU Information Bulletin No. 104. The IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide.
83% of all individual members are male, while 17% are female, among them the union's former president, Mexican astronomer Silvia Torres-Peimbert. Membership includes 79 national members, professional astronomical communities representing their country's affiliation with the IAU. National members include the Australian Academy of Science, the Chinese Astronomical Society, the French Academy of Sciences, the Indian National Science Academy, the National Academies, the National Research Foundation of South Africa, the National Scientific and Technical Research Council, KACST, the Council of German Observatories, the Royal Astronomical Society, the Royal Astronomical Society of New Zealand, the Royal Swedish Academy of Sciences, the Russian Academy of Sciences, the Science Council of Japan, among many others; the sovereign body of the IAU is its General Assembly. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union and elects various committees; the right to vote on matters brought before the Assembly varies according to the type of business under discussion.
The Statutes consider such business to be divided into two categories: issues of a "primarily scientific nature", upon which voting is restricted to individual members, all other matters, upon which voting is restricted to the representatives of national members. On budget matters, votes are weighted according to the relative subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid. An absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union. Since 1922, the IAU General Assembly meets every three years, with the ex
Naming of comets
Comets have been observed for the last 2,000 years. During that time, several different systems have been used to assign names to each comet, as a result many comets have more than one name; the simplest system names comets after the year. A convention arose of using the names of people associated with the discovery or the first detailed study of each comet. During the twentieth century, improvements in technology and dedicated searches led to a massive increase in the number of comet discoveries, which led to the creation of a numeric designation scheme; the original scheme assigned codes in the order. This scheme operated until 1994, when continued increases in the numbers of comets found each year resulted in the creation of a new scheme; this system, still in operation, assigns a code based on the type of orbit and the date of discovery. Before any systematic naming convention was adopted, comets were named in a variety of ways. Prior to the early 20th century, most comets were referred to by the year when they appeared e.g. the "Comet of 1702".
Bright comets which came to public attention would be described as the great comet of that year, such as the "Great Comet of 1680" and "Great Comet of 1882". If more than one great comet appeared in a single year, the month would be used for disambiguation e.g. the "Great January comet of 1910". Other additional adjectives might be used; the earliest comet to be named after a person was Caesar's Comet in 44 BC, so named because it was observed shortly after the assassination of Julius Caesar and was interpreted as a sign of his deification. Eponymous comets were named after the astronomer who conducted detailed investigations on them, or those who discovered the comet. After Edmond Halley demonstrated that the comets of 1531, 1607, 1682 were the same body and predicted its return in 1759, that comet became known as Halley's Comet; the second and third known periodic comets, Encke's Comet and Biela's Comet, were named after the astronomers who calculated their orbits rather than their original discoverers.
Periodic comets were named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their apparition. The first comet to be named after the person who discovered it, rather than the one who calculated its orbit, was Comet Faye – discovered by Hervé Faye in 1843. However, this convention did not become widespread until the early 20th century, it remains common today. A comet can be named after up to three discoverers, either working together as a team or making independent discoveries. For example, Comet Swift–Tuttle was first found by Lewis Swift and by Horace Parnell Tuttle a few days later. In recent years many comets have been discovered by large teams of astronomers, in this case comets may be named for the collaboration or instrument they used. For example, 160P/LINEAR was discovered by the Lincoln Near-Earth Asteroid Research team. Comet IRAS–Araki–Alcock was discovered independently by a team using the Infrared Astronomy Satellite and the amateur astronomers Genichi Araki and George Alcock.
In the past, when multiple comets were discovered by the same individual, group of individuals, or team, the comets' names were distinguished by adding a numeral to the discoverers' names. Today, the large numbers of comets discovered by some instruments makes this system impractical, no attempt is made to ensure that each comet is given a unique name. Instead, the comets' systematic designations are used to avoid confusion; until 1994, comets were first given a provisional designation consisting of the year of their discovery followed by a lowercase letter indicating its order of discovery in that year. Once the comet had been observed through perihelion and its orbit had been established, the comet was given a permanent designation of the year of its perihelion, followed by a Roman numeral indicating its order of perihelion passage in that year, so that Comet 1969i became Comet 1970 II Increasing numbers of comet discoveries made this procedure awkward, as did the delay between discovery and perihelion passage before the permanent name could be assigned.
As a result, in 1994 the International Astronomical Union approved a new naming system. Comets are now designated by the year of their discovery followed by a letter indicating the half-month of the discovery and a number indicating the order of discovery. For example, the fourth comet discovered in the second half of February 2006 was designated 2006 D4. Prefixes are added to indicate the nature of the comet: P/ indicates a periodic comet. C/ indicates a non-periodic comet. X / indicates a comet. D / indicates a periodic comet that has broken up, or been lost. A/ indicates an object, mistakenly identified as a comet, but is ac
Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, stars, nebulae and comets. More all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences; the early civilizations in recorded history, such as the Babylonians, Indians, Nubians, Chinese and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, but professional astronomy is now considered to be synonymous with astrophysics. Professional astronomy is split into theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, analyzed using basic principles of physics.
Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets. Astronomy means "law of the stars". Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are now distinct. Both of the terms "astronomy" and "astrophysics" may be used to refer to the same subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties," while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, dynamic processes of celestial objects and phenomena."
In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with subjects related to physics, modern astronomy could be called astrophysics; some fields, such as astrometry, are purely astronomy rather than astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics" depending on whether the department is affiliated with a physics department, many professional astronomers have physics rather than astronomy degrees; some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, Astronomy and Astrophysics. In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye; as civilizations developed, most notably in Mesopotamia, Persia, China and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, the nature of the Sun and the Earth in the Universe were explored philosophically; the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Ptolemaic system, named after Ptolemy.
A important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the astronomical traditions that developed in many other civilizations. The Babylonians discovered. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and inven
A comet is an icy, small Solar System body that, when passing close to the Sun and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, sometimes a tail; these phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice and small rocky particles; the coma may be up to 15 times the Earth's diameter, while the tail may stretch one astronomical unit. If sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been recorded since ancient times by many cultures. Comets have eccentric elliptical orbits, they have a wide range of orbital periods, ranging from several years to several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space; the appearance of a comet is called an apparition. Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus; this atmosphere has parts termed the tail. However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System; the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets.
In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3. 27 Manx comets were found from 2013 to 2017. As of July 2018 there are 6,339 known comets, a number, increasing as they are discovered. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. One comet per year is visible to the naked eye, though many of those are faint and unspectacular. Bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior; the word comet comētēs. That, in turn, is a latinisation of the Greek κομήτης, the Oxford English Dictionary notes that the term κομήτης meant "long-haired star, comet" in Greek.
Κομήτης was derived from κομᾶν, itself derived from κόμη and was used to mean "the tail of a comet". The astronomical symbol for comets is ☄; the solid, core structure of a comet is known as the nucleus. Cometary nuclei are composed of an amalgamation of rock, water ice, frozen carbon dioxide, carbon monoxide and ammonia; as such, they are popularly described as "dirty snowballs" after Fred Whipple's model. However, some comets may have a higher dust content, leading them to be called "icy dirtballs". Research conducted in 2014 suggests that comets are like "deep fried ice cream", in that their surfaces are formed of dense crystalline ice mixed with organic compounds, while the interior ice is colder and less dense; the surface of the nucleus is dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. In addition to the gases mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde and ethane and more complex molecules such as long-chain hydrocarbons and amino acids.
In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission. In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components may have been formed on asteroids and comets; the outer surfaces of cometary nuclei have a low albedo, making them among the least reflective objects found in the Solar System. The Giotto space probe found that the nucleus of Halley's Comet reflects about four percent of the light that falls on it, Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%. The dark surface material of the nucleus may consist of complex organic compounds. Solar heating drives off lighter volatile compounds, leaving behind larger organic compounds that tend to be dark, like tar or crude oil; the low reflectivity of cometary surfaces causes them to absorb t
Asteroids are minor planets of the inner Solar System. Larger asteroids have been called planetoids; these terms have been applied to any astronomical object orbiting the Sun that did not resemble a planet-like disc and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered they were found to have volatile-rich surfaces similar to comets; as a result, they were distinguished from objects found in the main asteroid belt. In this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There exist millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets; the vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects.
Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, S-type. These were named after and are identified with carbon-rich and silicate compositions, respectively; the sizes of asteroids varies greatly. Asteroids are differentiated from meteoroids. In the case of comets, the difference is one of composition: while asteroids are composed of mineral and rock, comets are composed of dust and ice. Furthermore, asteroids formed closer to the sun; the difference between asteroids and meteoroids is one of size: meteoroids have a diameter of one meter or less, whereas asteroids have a diameter of greater than one meter. Meteoroids can be composed of either cometary or asteroidal materials. Only one asteroid, 4 Vesta, which has a reflective surface, is visible to the naked eye, this only in dark skies when it is favorably positioned. Small asteroids passing close to Earth may be visible to the naked eye for a short time; as of October 2017, the Minor Planet Center had data on 745,000 objects in the inner and outer Solar System, of which 504,000 had enough information to be given numbered designations.
The United Nations declared 30 June as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, Russian Federation, on 30 June 1908. In April 2018, the B612 Foundation reported "It's 100 percent certain we'll be hit, but we're not 100 percent sure when." In 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched; the first asteroid to be discovered, was considered to be a new planet.
This was followed by the discovery of other similar bodies, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term "asteroid", coined in Greek as ἀστεροειδής, or asteroeidēs, meaning'star-like, star-shaped', derived from the Ancient Greek ἀστήρ astēr'star, planet'. In the early second half of the nineteenth century, the terms "asteroid" and "planet" were still used interchangeably. Overview of discovery timeline: 10 by 1849 1 Ceres, 1801 2 Pallas – 1802 3 Juno – 1804 4 Vesta – 1807 5 Astraea – 1845 in 1846, planet Neptune was discovered 6 Hebe – July 1847 7 Iris – August 1847 8 Flora – October 1847 9 Metis – 25 April 1848 10 Hygiea – 12 April 1849 tenth asteroid discovered 100 asteroids by 1868 1,000 by 1921 10,000 by 1989 100,000 by 2005 ~700,000 by 2015 Asteroid discovery methods have improved over the past two centuries.
In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the missing planet predicted at about 2.8 AU from the Sun by the Titius-Bode law because of the discovery, by Sir William Herschel in 1781, of the planet Uranus at the distance predicted by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would be spotted; the expected motion of the missing planet was about 30 seconds of arc per hour discernible by observers. The first object, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily, he discovered a new star-like object in Taurus and followed the displacement of this object during several nights. That year, Carl Friedrich Gauss used these observations to calculate the orbit of this unknown object, found to be between the planets Mars and Jupiter.
Piazzi named it after Ceres, the Roman goddess of agriculture. Three other asteroids (2 Pallas, 3 Juno, 4 Ves