The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic escape orbit, greater than 1 is a hyperbola; the term derives its name from the parameters of conic sections, as every Kepler orbit is a conic section. It is used for the isolated two-body problem, but extensions exist for objects following a Klemperer rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit; the eccentricity of this Kepler orbit is a non-negative number. The eccentricity may take the following values: circular orbit: e = 0 elliptic orbit: 0 < e < 1 parabolic trajectory: e = 1 hyperbolic trajectory: e > 1 The eccentricity e is given by e = 1 + 2 E L 2 m red α 2 where E is the total orbital energy, L is the angular momentum, mred is the reduced mass, α the coefficient of the inverse-square law central force such as gravity or electrostatics in classical physics: F = α r 2 or in the case of a gravitational force: e = 1 + 2 ε h 2 μ 2 where ε is the specific orbital energy, μ the standard gravitational parameter based on the total mass, h the specific relative angular momentum.
For values of e from 0 to 1 the orbit's shape is an elongated ellipse. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola. Radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits hence eccentricity equal to one. Keeping the energy constant and reducing the angular momentum, elliptic and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the hyperbolic trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a perfect circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, one must calculate the inverse sine to find the projection angle of 11.86 degrees. Next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity; the word "eccentricity" comes from Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros "out of the center", from ἐκ- ek-, "out of" + κέντρον kentron "center".
"Eccentric" first appeared in English in 1551, with the definition "a circle in which the earth, sun. Etc. deviates from its center". By five years in 1556, an adjectival form of the word had developed; the eccentricity of an orbit can be calculated from the orbital state vectors as the magnitude of the eccentricity vector: e = | e | where: e is the eccentricity vector. For elliptical orbits it can be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p = 1 − 2 r a r p + 1 where: ra is the radius at apoapsis. Rp is the radius at periapsis; the eccentricity of an elliptical orbit can be used to obtain the ratio of the periapsis to the apoapsis: r p r a = 1 − e 1 + e For Earth, orbital eccentricity ≈ 0.0167, apoapsis= aphelion and periapsis= perihelion relative to sun. For Earth's annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈ 1.034 relative to center point of path. The eccentricity of the Earth's orbit is about 0.0167.
Proper orbital elements
The proper orbital elements of an orbit are constants of motion of an object in space that remain unchanged over an astronomically long timescale. The term is used to describe the three quantities: proper semimajor axis, proper eccentricity, proper inclination; the proper elements can be contrasted with the osculating Keplerian orbital elements observed at a particular time or epoch, such as the semi-major axis and inclination. Those osculating elements change in a quasi-periodic and predictable manner due to such effects as perturbations from planets or other bodies, precession. In the Solar System, such changes occur on timescales of thousands of years, while proper elements are meant to be constant over at least tens of millions of years. For most bodies, the osculating elements are close to the proper elements because precession and perturbation effects are small. For over 99% of asteroids in the asteroid belt, the differences are less than 0.02 AU, 0.1, 2°. This difference is non-negligible for any purposes where precision is of importance.
As an example, the asteroid Ceres has osculating orbital elements while its proper orbital elements are A notable exception to this small-difference rule are asteroids lying in the Kirkwood gaps, which are in strong orbital resonance with Jupiter. To obtain proper elements for an object, one conducts a detailed simulation of its motion over timespans of several millions of years; such a simulation must take into account many details of celestial mechanics including perturbations by the planets. Subsequently, one extracts quantities from the simulation which remain unchanged over this long timespan; these are the proper orbital elements. Various approximate analytic calculations were made, starting with those of Kiyotsugu Hirayama in the early 20th century. Analytic methods included thousands of perturbing corrections for each particular object. Presently, the method of choice is to use a computer to numerically integrate the equations of celestial dynamics, extract constants of motion directly from a numerical analysis of the predicted positions.
At present the most prominent use of proper orbital elements is in the study of asteroid families, following in the footsteps of the pioneering work of Hirayama. A Mars-crosser asteroid 132 Aethra is the lowest numbered asteroid to not have any proper orbital elements. Hirayama family Perturbation Z. Knežević et al; the Determination of Asteroid Proper Elements, p. 603-612 in Asteroids III, University of Arizona Press. Z. Knežević: COMPUTATION OF ASTEROID PROPER ELEMENTS: RECENT ADVANCES, Serbian Astronomical Journal, vol. 195, pp. 1-8. Latest calculations of proper elements for numbered minor planets at astDys. Asteroid proper orbital elements dataset at Asteroid Families Portal
The Koronis or Koronian family known as the Lacrimosa family, is a large asteroid family of stony asteroids, located in the outer region of the asteroid belt. They are thought to have been formed at least two billion years ago in a catastrophic collision between two larger bodies; the family is named after 158 Koronis, the largest known member is about 41 km in diameter. The Koronis family travels in a cluster along the same orbit, it has 5949 members. This family has two subfamilies; the Karin family was formed remarkably in a catastrophic collision, with an estimated age of 5.72 million years. The Koronis family with 246 members is the other, it formed 15 million years ago by a non-catastrophic collision with 158 Koronis. On August 28, 1993, the Galileo spacecraft visited a member of 243 Ida. A photo of Ida is part of the composite image at right. Astronomical studies of the Koronis Family Spins on Koronis family
The Flora family is a prominent family of stony asteroids located in the inner region of the asteroid belt. It is one of the largest families with more than 13,000 known members, or 3.5% of all main-belt asteroids. The origin and properties of this family are poorly understood, it is a broad family which fades into the surrounding background population. While the largest members, 8 Flora and 43 Ariadne, are located near the edge, there are several distinct groupings within the family created by secondary collisions. Due to this complex internal structure and the poorly defined boundaries, the Flora family has been described as an asteroid clan. Only few interlopers have been identified; this family may be the source of the impactor that formed the Chicxulub crater, the culprit in the extinction of the dinosaurs. The largest member is 8 Flora, which measures 140 km in diameter, comprises about 80% of the total family mass; the parent body was certainly disrupted by the impact/s that formed the family, Flora is a gravitational aggregate of most of the pieces.
43 Ariadne makes up much of the remaining mass. Because of the family's poorly defined boundaries, the location of Flora itself near the edge, it has been called the "Ariadne family", when Flora did not make it into the group during an analysis; the remaining family members being small, below 30 km in diameter. A noticeable fraction of the parent body has been lost from the family since the original impact due to processes such as e.g. secondary collisions. For example, it has been estimated that Flora contains only about 57% of the parent body's mass, but about 80% of the mass in the present family; the Flora family is broad and fades into the background population in such a way that its boundaries are poorly defined. There are several non-uniformities or lobes within the family, one cause of which may have been secondary collisions between family members. Hence, it is a classical example of a so-called asteroid clan. Curiously, the largest members, 8 Flora and 43 Ariadne, are located near the edge of the family.
The reason for this unusual mass distribution within the family is unknown at present. 951 Gaspra, a medium-sized core family member, was visited by the Galileo spacecraft on its way to Jupiter, is one of the most extensively studied asteroids. Studies of Gaspra suggests that the family's age is of the order of 200 million years, that the parent body was at least differentiated; the Flora family members are considered good candidates for being the parent bodies of the L chondrite meteorites, which contribute about 38% of all meteorites impacting the Earth. This theory is supported by the family's location close to the unstable zone of the ν 6 secular resonance, because the spectral properties of family members are consistent with being the parent bodies of this meteorite type; the Flora family was one of the five original Hirayama families. It has a high number of early discovered members both because S-type asteroids tend to have high albedo, because it is the closest major asteroid grouping to Earth.
A HCM numerical analysis by Vincenzo Zappalà in 1995 determined a large group of'core' family members, whose proper orbital elements lie in the approximate ranges The boundaries of the family are, however indistinct. At the present epoch, the range of osculating orbital elements of these core members is Zappalà's 1995 analysis found 604 core members, 1027 in a wider group. A search of a recent proper element database for 96944 minor planets in 2005 yielded 7438 objects lying within the rectangular-shaped region defined by the first table above. However, this includes parts of the Vesta and Nysa families in the corners so that a more membership estimate is 4000–5000 objects; this means. Because of the high background density of asteroids in this part of space, one might expect that a great number of interlopers would be present. However, few have been identified; this is because interlopers are hard to distinguish from family members because the family is of the same spectral type that dominates the inner main belt overall.
The few interlopers that have been identified are all small They include 298 Baptistina, 422 Berolina, 2093 Genichesk, 2259 Sofievka, 2952 Lilliputia, 453 Tea, 3533 Toyota, 3850 Peltier, 3875 Staehle, 4278 Harvey, 4396 Gressmann, 4750 Mukai. Zappalà, Vincenzo. PDS asteroid taxonomy data set Bus, Schelte J.. Data set online here. Nesvorný, D. et al.. AstDys site. Proper element
Japan is an island country in East Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asian continent and stretches from the Sea of Okhotsk in the north to the East China Sea and the Philippine Sea in the south; the kanji that make up Japan's name mean "sun origin", it is called the "Land of the Rising Sun". Japan is a stratovolcanic archipelago consisting of about 6,852 islands; the four largest are Honshu, Hokkaido and Shikoku, which make up about ninety-seven percent of Japan's land area and are referred to as home islands. The country is divided into 47 prefectures in eight regions, with Hokkaido being the northernmost prefecture and Okinawa being the southernmost one; the population of 127 million is the world's tenth largest. 90.7 % of people live in cities. About 13.8 million people live in the capital of Japan. The Greater Tokyo Area is the most populous metropolitan area in the world with over 38 million people. Archaeological research indicates; the first written mention of Japan is in Chinese history texts from the 1st century AD.
Influence from other regions China, followed by periods of isolation from Western Europe, has characterized Japan's history. From the 12th century until 1868, Japan was ruled by successive feudal military shōguns who ruled in the name of the Emperor. Japan entered into a long period of isolation in the early 17th century, ended in 1853 when a United States fleet pressured Japan to open to the West. After nearly two decades of internal conflict and insurrection, the Imperial Court regained its political power in 1868 through the help of several clans from Chōshū and Satsuma – and the Empire of Japan was established. In the late 19th and early 20th centuries, victories in the First Sino-Japanese War, the Russo-Japanese War and World War I allowed Japan to expand its empire during a period of increasing militarism; the Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the Japanese surrender. Since adopting its revised constitution on May 3, 1947, during the occupation led by SCAP, the sovereign state of Japan has maintained a unitary parliamentary constitutional monarchy with an Emperor and an elected legislature called the National Diet.
Japan is a member of the ASEAN Plus mechanism, UN, the OECD, the G7, the G8, the G20, is considered a great power. Its economy is the world's third-largest by nominal GDP and the fourth-largest by purchasing power parity, it is the world's fourth-largest exporter and fourth-largest importer. Japan benefits from a skilled and educated workforce. Although it has renounced its right to declare war, Japan maintains a modern military with the world's eighth-largest military budget, used for self-defense and peacekeeping roles. Japan is a developed country with a high standard of living and Human Development Index, its population enjoys the highest life expectancy and third lowest infant mortality rate in the world, but is experiencing issues due to an aging population and low birthrate. Japan is renowned for its historical and extensive cinema, influential music industry, video gaming, rich cuisine and its major contributions to science and modern technology; the Japanese word for Japan is 日本, pronounced Nihon or Nippon and means "the origin of the sun".
The character nichi means "sun" or "day". The compound therefore means "origin of the sun" and is the source of the popular Western epithet "Land of the Rising Sun"; the earliest record of the name Nihon appears in the Chinese historical records of the Tang dynasty, the Old Book of Tang. At the end of the seventh century, a delegation from Japan requested that Nihon be used as the name of their country; this name may have its origin in a letter sent in 607 and recorded in the official history of the Sui dynasty. Prince Shōtoku, the Regent of Japan, sent a mission to China with a letter in which he called himself "the Emperor of the Land where the Sun rises"; the message said: "Here, I, the emperor of the country where the sun rises, send a letter to the emperor of the country where the sun sets. How are you". Prior to the adoption of Nihon, other terms such as Yamato and Wakoku were used; the term Wa is a homophone of Wo 倭, used by the Chinese as a designation for the Japanese as early as the third century Three Kingdoms period.
Another form of Wa, Wei in Chinese) was used for an early state in Japan called Nakoku during the Han dynasty. However, the Japanese disliked some connotation of Wa 倭, it was therefore replaced with the substitute character Wa, meaning "togetherness, harmony"; the English word Japan derives from the historical Chinese pronunciation of 日本. The Old Mandarin or early Wu Chinese pronunciation of Japan was recorded by Marco Polo as Cipangu. In modern Shanghainese, a Wu dialect, the pronunciation of characters 日本; the old Malay word for Japan, Japun or Japang, was borrowed from a southern coastal Chinese dialect Fukienese or Ningpo – and this Malay word was encountered by Portuguese traders in Southeast Asia in the 16th century. These Early Portuguese traders brought the word
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
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