The Southern Hemisphere is the half of Earth, south of the Equator. It contains parts of five continents, four oceans and most of the Pacific Islands in Oceania, its surface is 80.9% water, compared with 60.7% water in the case of the Northern Hemisphere, it contains 32.7% of Earth's land. Owing to the tilt of Earth's rotation relative to the Sun and the ecliptic plane, summer is from December to March and winter is from June to September. September 22 or 23 is the vernal equinox and March 20 or 21 is the autumnal equinox; the South Pole is in the center of the southern hemispherical region. Southern Hemisphere climates tend to be milder than those at similar latitudes in the Northern Hemisphere, except in the Antarctic, colder than the Arctic; this is because the Southern Hemisphere has more ocean and much less land. The differences are attributed to oceanic heat transfer and differing extents of greenhouse trapping. In the Southern Hemisphere the sun passes from east to west through the north, although north of the Tropic of Capricorn the mean sun can be directly overhead or due north at midday.
The Sun rotating through the north causes an apparent right-left trajectory through the sky unlike the left-right motion of the Sun when seen from the Northern Hemisphere as it passes through the southern sky. Sun-cast shadows turn anticlockwise throughout the day and sundials have the hours increasing in the anticlockwise direction. During solar eclipses viewed from a point to the south of the Tropic of Capricorn, the Moon moves from left to right on the disc of the Sun, while viewed from a point to the north of the Tropic of Cancer, the Moon moves from right to left during solar eclipses. Cyclones and tropical storms spin clockwise in the Southern Hemisphere due to the Coriolis effect; the southern temperate zone, a subsection of the Southern Hemisphere, is nearly all oceanic. This zone includes the southern tip of South Africa; the Sagittarius constellation that includes the galactic centre is a southern constellation and this, combined with clearer skies, makes for excellent viewing of the night sky from the Southern Hemisphere with brighter and more numerous stars.
Forests in the Southern Hemisphere have special features which set them apart from those in the Northern Hemisphere. Both Chile and Australia share, for example, unique beech species or Nothofagus, New Zealand has members of the related genera Lophozonia and Fuscospora; the eucalyptus is native to Australia but is now planted in Southern Africa and Latin America for pulp production and biofuel uses. 800 million humans live in the Southern Hemisphere, representing only 10–12% of the total global human population of 7.3 billion. Of those 800 million people, 200 million live in Brazil, the largest country by land area in the Southern Hemisphere, while 141 million live on the island of Java, the most populous island in the world; the most populous nation in the Southern Hemisphere is Indonesia, with 261 million people. Portuguese is the most spoken language in the Southern Hemisphere, followed by Javanese; the largest metropolitan areas in the Southern Hemisphere are São Paulo, Buenos Aires, Rio de Janeiro and Sydney.
The most important financial and commercial centers in the Southern Hemisphere are São Paulo, where the Bovespa Index is headquartered, along with Sydney, home to the Australian Securities Exchange, home to the Johannesburg Stock Exchange and Buenos Aires, headquarters of the Buenos Aires Stock Exchange, the oldest stock market in the Southern Hemisphere. Among the most developed nations in the Southern Hemisphere are Australia, with a nominal GDP per capita of US$51,850 and a Human Development Index of 0.939, the second highest in the world as of 2016. New Zealand is well developed, with a nominal GDP per capita of US$38,385 and a Human Development Index of 0.915, putting it at #13 in the world in 2016. The least developed nations in the Southern Hemisphere cluster in Africa and Oceania, with Burundi and Mozambique at the lowest ends of the Human Development Index, at 0.404 and 0.418 respectively. The nominal GDP per capitas of these two countries don't go above US$550 per capita, a tiny fraction of the incomes enjoyed by Australians and New Zealanders.
The most widespread religions in the Southern Hemisphere are Christianity in South America, southern Africa and Australia/New Zealand, followed by Islam in most of the islands of Indonesia and in parts of southeastern Africa, Hinduism, concentrated on the island of Bali and neighboring islands. The oldest continuously inhabited city in the Southern Hemisphere is Bogor, in western Java, founded in 669 CE. Ancient texts from the Hindu kingdoms prevalent in the area definitively record 669 CE as the year when Bogor was founded. However, there is some evidence that Zanzibar, an ancient port with around 200,000 inhabitants on
The Anglo-Saxons were a cultural group who inhabited Great Britain from the 5th century, the direct ancestors of the majority of the modern British people. They comprise people from Germanic tribes who migrated to the island from continental Europe, their descendants, indigenous British groups who adopted many aspects of Anglo-Saxon culture and language; the Anglo-Saxon period denotes the period in Britain between about 450 and 1066, after their initial settlement and up until the Norman conquest. The early Anglo-Saxon period includes the creation of an English nation, with many of the aspects that survive today, including regional government of shires and hundreds. During this period, Christianity was established and there was a flowering of literature and language. Charters and law were established; the term Anglo-Saxon is popularly used for the language, spoken and written by the Anglo-Saxons in England and eastern Scotland between at least the mid-5th century and the mid-12th century. In scholarly use, it is more called Old English.
The history of the Anglo-Saxons is the history of a cultural identity. It developed from divergent groups in association with the people's adoption of Christianity, was integral to the establishment of various kingdoms. Threatened by extended Danish invasions and military occupation of eastern England, this identity was re-established; the visible Anglo-Saxon culture can be seen in the material culture of buildings, dress styles, illuminated texts and grave goods. Behind the symbolic nature of these cultural emblems, there are strong elements of tribal and lordship ties; the elite declared themselves as kings who developed burhs, identified their roles and peoples in Biblical terms. Above all, as Helena Hamerow has observed, "local and extended kin groups remained...the essential unit of production throughout the Anglo-Saxon period." The effects persist in the 21st century as, according to a study published in March 2015, the genetic makeup of British populations today shows divisions of the tribal political units of the early Anglo-Saxon period.
Use of the term Anglo-Saxon assumes that the words Angles, Saxons or Anglo-Saxon have the same meaning in all the sources. This term began to be used only in the 8th century to distinguish "Germanic" groups in Britain from those on the continent. Catherine Hills summarised the views of many modern scholars in her observation that attitudes towards Anglo-Saxons, hence the interpretation of their culture and history, have been "more contingent on contemporary political and religious theology as on any kind of evidence." The Old English ethnonym "Angul-Seaxan" comes from the Latin Angli-Saxones and became the name of the peoples Bede calls Anglorum and Gildas calls Saxones. Anglo-Saxon is a term, used by Anglo-Saxons themselves, it is they identified as ængli, Seaxe or, more a local or tribal name such as Mierce, Gewisse, Westseaxe, or Norþanhymbre. The use of Anglo-Saxon disguises the extent to which people identified as Anglo-Scandinavian after the Viking age, or as Anglo-Norman after the Norman conquest in 1066.
The earliest historical references using this term are from outside Britain, referring to piratical Germanic raiders,'Saxones' who attacked the shores of Britain and Gaul in the 3rd century AD. Procopius states that Britain was settled by three races: the Angiloi and Britons; the term Angli Saxones seems to have first been used in continental writing of the 8th century. The name therefore seemed to mean "English" Saxons; the Christian church seems to have used the word Angli. The terms ænglisc and Angelcynn were used by West Saxon King Alfred to refer to the people; the first use of the term Anglo-Saxon amongst the insular sources is in the titles for Athelstan: Angelsaxonum Denorumque gloriosissimus rex and rex Angulsexna and Norþhymbra imperator paganorum gubernator Brittanorumque propugnator. At other times he uses the term rex Anglorum, which meant both Anglo-Saxons and Danes. Alfred the Great used Anglosaxonum Rex; the term Engla cyningc is used by Æthelred. King Cnut in 1021 was the first to refer to the land and not the people with this term: ealles Englalandes cyningc.
These titles express the sense that the Anglo-Saxons were a Christian people with a king anointed by God. The indigenous Common Brittonic speakers referred to Anglo-Saxons as Saxones or Saeson. Catherine Hills suggests that it is no accident, "that the English call themselves by the name sanctified by the Church, as that of a people chosen by God, whereas their enemies use the name applied to piratical raiders"; the early Anglo-Saxon period covers the history of medieval Britain that starts from the end of Roman rul
A day is the period of time during which the Earth completes one rotation around its axis. A solar day is the length of time which elapses between the Sun reaching its highest point in the sky two consecutive times. In 1960, the second was redefined in terms of the orbital motion of the Earth in year 1900, was designated the SI base unit of time; the unit of measurement "day", was symbolized d. In 1967, the second and so the day were redefined by atomic electron transition. A civil day is 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time, plus or minus an hour in those locations that change from or to daylight saving time. Day can be defined as each of the twenty-four-hour periods, reckoned from one midnight to the next, into which a week, month, or year is divided, corresponding to a rotation of the earth on its axis; however its use depends on its context, for example when people say'day and night','day' will have a different meaning. It will mean the interval of light between two successive nights.
However, in order to be clear when using'day' in that sense, "daytime" should be used to distinguish it from "day" referring to a 24-hour period. The word day may refer to a day of the week or to a calendar date, as in answer to the question, "On which day?" The life patterns of humans and many other species are related to Earth's solar day and the day-night cycle. Several definitions of this universal human concept are used according to context and convenience. Besides the day of 24 hours, the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the solar day, defined as the time it takes for the Sun to return to its culmination point; because celestial orbits are not circular, thus objects travel at different speeds at various positions in their orbit, a solar day is not the same length of time throughout the orbital year. Because the Earth orbits the Sun elliptically as the Earth spins on an inclined axis, this period can be up to 7.9 seconds more than 24 hours.
In recent decades, the average length of a solar day on Earth has been about 86 400.002 seconds and there are about 365.2422 solar days in one mean tropical year. Ancient custom has a new day start at either the setting of the Sun on the local horizon; the exact moment of, the interval between, two sunrises or sunsets depends on the geographical position, the time of year. A more constant day can be defined by the Sun passing through the local meridian, which happens at local noon or midnight; the exact moment is dependent on the geographical longitude, to a lesser extent on the time of the year. The length of such a day is nearly constant; this is the time as indicated by modern sundials. A further improvement defines a fictitious mean Sun that moves with constant speed along the celestial equator. A day, understood as the span of time it takes for the Earth to make one entire rotation with respect to the celestial background or a distant star, is called a stellar day; this period of rotation is about 4 minutes less than 24 hours and there are about 366.2422 stellar days in one mean tropical year.
Other planets and moons have solar days of different lengths from Earth's. A day, in the sense of daytime, distinguished from night time, is defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles; the length of daytime averages more than half of the 24-hour day. Two effects make daytime on average longer than nights; the Sun has an apparent size of about 32 minutes of arc. Additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc. Thus, daytime is on average around 7 minutes longer than 12 hours; the term comes from the Old English dæg, with its cognates such as dagur in Icelandic, Tag in German, dag in Norwegian, Danish and Dutch. All of them from the Indo-European root dyau which explains the similarity with Latin dies though the word is known to come from the Germanic branch.
As of October 17, 2015, day is the 205th most common word in US English, the 210th most common in UK English. A day, symbol d, defined as 86 400 seconds, is not an SI unit, but is accepted for use with SI; the Second is the base unit of time in SI units. In 1967–68, during the 13th CGPM, the International Bureau of Weights and Measures redefined a second as … the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium 133 atom; this makes the SI-based day last 794 243 384 928 000 of those periods. Due to tidal effects, the
The Roman calendar was the calendar used by the Roman kingdom and republic. The term includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1st century BC and sometimes includes any system dated by inclusive counting towards months' kalends and ides in the Roman manner; the term excludes the Alexandrian calendar of Roman Egypt, which continued the unique months of that land's former calendar. Roman dates were counted inclusively forward to the next of three principal days: the first of the month, a day less than the middle of the month, eight days—nine, counting inclusively—before this; the original calendar consisted of 10 months beginning in spring with March. These months ran for 38 nundinal cycles, each forming an eight-day week ended by religious rituals and a public market; the winter period was divided into two months and February. The legendary early kings Romulus and Numa Pompilius were traditionally credited with establishing this early fixed calendar, which bears traces of its origin as an observational lunar one.
In particular, the kalends and ides seem to have derived from the first sighting of the crescent moon, the first-quarter moon, the full moon respectively. The system ran well short of the solar year, it needed constant intercalation to keep religious festivals and other activities in their proper seasons. For superstitious reasons, such intercalation occurred within the month of February after it was no longer considered the last month. After the establishment of the Roman Republic, years began to be dated by consulships and control over intercalation was granted to the pontifices, who abused their power by lengthening years controlled by their political allies and shortening the years in their rivals' terms of office. Having won his war with Pompey, Caesar used his position as Rome's chief pontiff to enact a calendar reform in 46 BC, coincidentally making the year of his third consulship last for 446 days. In order to avoid interfering with Rome's religious ceremonies, the reform added all its days towards the ends of months and did not adjust any nones or ides in months which came to have 31 days.
The Julian calendar was supposed to have a single leap day on 24 February every fourth year but following Caesar's assassination the priests figured this using inclusive counting and mistakenly added the bissextile day every three years. In order to bring the calendar back to its proper place, Augustus was obliged to suspend intercalation for one or two decades; the revised calendar remaining longer than the solar year, the date of Easter shifted far enough away from the vernal equinox that Pope Gregory XIII ordered its adjustment in the 16th century. The original Roman calendar is believed to have been an observational lunar calendar whose months began from the first signs of a new crescent moon; because a lunar cycle is about 29 1⁄2 days long, such months would have varied between 29 and 30 days. Twelve such months would have fallen 11 days short of the solar year. Given the seasonal aspects of the calendar and its associated religious festivals, this was avoided through some form of intercalation or through the suspension of the calendar during winter.
Rome's 8-day week, the nundinal cycle, was shared with the Etruscans, who used it as the schedule of royal audiences. It was a part of the early calendar and was credited in Roman legend variously to Romulus and Servius Tullius; the Romans themselves described their first organized year as one with ten fixed months, each of 30 or 31 days. Such a decimal division fitted general Roman practice; the four 31-day months were called "full" and the others "hollow". Its 304 days made up 38 nundinal cycles; the system is said to have left the remaining 50-odd days of the year as an unorganized "winter", although Licinius Macer's lost history stated the earliest Roman calendar employed intercalation instead and Macrobius claims the 10-month calendar was allowed to shift until the summer and winter months were misplaced, at which time additional days belonging to no month were inserted into the calendar until it seemed things were restored to their proper place. Roman writers credited this calendar to Romulus, their legendary first king and culture hero, although this was common with other practices and traditions whose origin had been lost to them.
Some scholars doubt the existence of this calendar at all, as it is only attested in late Republican and Imperial sources and supported only by the misplaced names of the months from September to December. Rüpke finds the coincidence of the length of the supposed "Romulan" year with the length of the first ten months of the Julian calendar to be suspicious. Other traditions existed alongside this one, however. Plutarch's Parallel Lives recounts that Romulus's calendar had been solar but adhered to the general principle that the year should last for 360 days. Months were employed secondarily and haphazardly, with some counted as 20 days and others as 35 or more; the attested calendar of the Roman Republic was quite different. It followed Gre
Spring is one of the four temperate seasons, following winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate and customs; when it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox and nights are twelve hours long, with day length increasing and night length decreasing as the season progresses. Spring and "springtime" refer to the season, to ideas of rebirth, renewal and regrowth. Subtropical and tropical areas have climates better described in terms of other seasons, e.g. dry or wet, monsoonal or cyclonic. Cultures may have local names for seasons which have little equivalence to the terms originating in Europe. Meteorologists define four seasons in many climatic areas: spring, summer and winter; these are demarcated by the values of their average temperatures on a monthly basis, with each season lasting three months. The three warmest months are by definition summer, the three coldest months are winter and the intervening gaps are spring and autumn.
Spring, when defined in this manner, can start on different dates in different regions. Thus, in the US and UK, spring months are March and May, while in New Zealand and Australia, spring conventionally begins on September 1 and ends November 30. Swedish meteorologists define the beginning of spring as the first occasion on which the average daytime temperature exceeds zero degrees Celsius for seven consecutive days, thus the date varies with latitude and elevation. In some cultures in the Northern Hemisphere, the astronomical vernal equinox is taken to mark the first day of spring, the summer solstice is taken as the first day of summer. In Persian culture the first day of spring is the first day of the first month which begins on 20 or 21 March. In other traditions, the equinox is taken as mid-spring. In the traditional Chinese calendar, the "spring" season consists of the days between Lichun, taking Chunfen as its midpoint ending at Lixia. According to the Celtic tradition, based on daylight and the strength of the noon sun, spring begins in early February and continues until early May.
The beginning of spring is not always determined by fixed calendar dates. The phenological or ecological definition of spring relates to biological indicators, such as the blossoming of a range of plant species, the activities of animals, the special smell of soil that has reached the temperature for micro flora to flourish; these indicators, along with the beginning of spring, vary according to the local climate and according to the specific weather of a particular year. Most ecologists divide the year into six seasons. In addition to spring, ecological reckoning identifies an earlier separate prevernal season between the hibernal and vernal seasons; this is a time when only the hardiest flowers like the crocus are in bloom, sometimes while there is still some snowcover on the ground. During early spring, the axis of the Earth is increasing its tilt relative to the Sun, the length of daylight increases for the relevant hemisphere; the hemisphere begins to warm causing new plant growth to "spring forth," giving the season its name.
Any snow begins to melt, swelling streams with runoff and any frosts become less severe. In climates that have no snow, rare frosts and ground temperatures increase more rapidly. Many flowering plants bloom at this time of year, in a long succession, sometimes beginning when snow is still on the ground and continuing into early summer. In snowless areas, "spring" may begin as early as February or August, heralded by the blooming of deciduous magnolias and quince. Many temperate areas have a dry spring, wet autumn, which brings about flowering in this season, more consistent with the need for water, as well as warmth. Subarctic areas may not experience "spring" at all until May. While spring is a result of the warmth caused by the changing orientation of the Earth's axis relative to the Sun, the weather in many parts of the world is affected by other, less predictable events; the rainfall in spring follows trends more related to longer cycles—such as the solar cycle—or events created by ocean currents and ocean temperatures—for example, the El Niño effect and the Southern Oscillation Index.
Unstable spring weather may occur more when warm air begins to invade from lower latitudes, while cold air is still pushing from the Polar regions. Flooding is most common in and near mountainous areas during this time of year, because of snow-melt, accelerated by warm rains. In North America, Tornado Alley is most active at this time of year since the Rocky Mountains prevent the surging hot and cold air masses from spreading eastward, instead force them into direct conflict. Besides tornadoes, supercell thunderstorms can produce dangerously large hail and high winds, for which a severe thunderstorm warning or tornado warning is issued. More so than in winter, the jet streams play an important role in unstable and severe Northern Hemisphere weather in springtime. In recent decades, season creep has been observed, which means that many phenological signs of spring are occurring earlier in many regions by around two days per decade. Spring in the Southern Hemisphere is different in several significant ways to that of the Northern Hemisphere
French Republican calendar
The French Republican calendar commonly called the French Revolutionary calendar, was a calendar created and implemented during the French Revolution, used by the French government for about 12 years from late 1793 to 1805, for 18 days by the Paris Commune in 1871. The revolutionary system was designed in part to remove all religious and royalist influences from the calendar, was part of a larger attempt at decimalisation in France, it was used in government records in France and other areas under French rule, including Belgium and parts of the Netherlands, Switzerland and Italy. Sylvain Maréchal, prominent anticlerical atheist, published the first edition of his Almanach des Honnêtes-gens in 1788. On pages 14–15 appears a calendar, consisting of twelve months; the first month is "Mars, ou Princeps", the last month is "Février, ou Duodécembre". The lengths of the months are the same as the lengths given them by Julius Caesar. Individual days were assigned, instead of to the traditional saints, to people noteworthy for secular achievements.
Editions of the almanac would switch to the Republican Calendar. The days of the French Revolution and Republic saw many efforts to sweep away various trappings of the ancien régime; the new Republican government sought to institute, among other reforms, a new social and legal system, a new system of weights and measures, a new calendar. Amid nostalgia for the ancient Roman Republic, the theories of the Enlightenment were at their peak, the devisers of the new systems looked to nature for their inspiration. Natural constants, multiples of ten, Latin as well as Ancient Greek derivations formed the fundamental blocks from which the new systems were built; the new calendar was created by a commission under the direction of the politician Charles-Gilbert Romme seconded by Claude Joseph Ferry and Charles-François Dupuis. They associated with their work the chemist Louis-Bernard Guyton de Morveau, the mathematician and astronomer Joseph-Louis Lagrange, the astronomer Joseph Jérôme Lefrançois de Lalande, the mathematician Gaspard Monge, the astronomer and naval geographer Alexandre Guy Pingré, the poet and playwright Fabre d'Églantine, who invented the names of the months, with the help of André Thouin, gardener at the Jardin des Plantes of the Muséum National d'Histoire Naturelle in Paris.
As the rapporteur of the commission, Charles-Gilbert Romme presented the new calendar to the Jacobin-controlled National Convention on 23 September 1793, which adopted it on 24 October 1793 and extended it proleptically to its epoch of 22 September 1792. It is because of his position as rapporteur of the commission that the creation of the republican calendar is attributed to Romme; the calendar is named the "French Revolutionary Calendar" because it was created during the Revolution, but this is a slight misnomer. Indeed, there was a debate as to whether the calendar should celebrate the Great Revolution, which began in July 1789, or the Republic, established in 1792. Following 14 July 1789, papers and pamphlets started calling 1789 year I of Liberty and the following years II and III, it was in 1792, with the practical problem of dating financial transactions, that the legislative assembly was confronted with the problem of the calendar. The choice of epoch was either 1 January 1789 or 14 July 1789.
After some hesitation the assembly decided on 2 January 1792 that all official documents would use the "era of Liberty" and that the year IV of Liberty started on 1 January 1792. This usage was modified on 22 September 1792 when the Republic was proclaimed and the Convention decided that all public documents would be dated Year I of the French Republic; the decree of 2 January 1793 stipulated that the year II of the Republic began on 1 January 1793. The establishment of the Republic was used as the epochal date for the calendar. In France, it is known as the calendrier républicain as well as the calendrier révolutionnaire. French coins of the period used this calendar. Many show the year in Arabic numbers. Year 11 coins have a "XI" date to avoid confusion with the Roman "II"; the French Revolution is considered to have ended with the coup of 18 Brumaire, Year VIII, the coup d'état of Napoleon Bonaparte against the established constitutional regime of the Directoire. The Concordat of 1801 re-established the Roman Catholic Church as an official institution in France, although not as the state religion of France.
The concordat took effect from Easter Sunday, 28 Germinal, Year XI.
A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so all of them disintegrate and never hit the Earth's surface. Intense or unusual meteor showers are known as meteor outbursts and meteor storms, which produce at least 1,000 meteors an hour, most notably from the Leonids; the Meteor Data Centre lists over 900 suspected meteor showers of which about 100 are well established. Several organizations point to viewing opportunities on the Internet; the first great meteor storm in the modern era was the Leonids of November 1833. One estimate is a peak rate of over one hundred thousand meteors an hour, but another, done as the storm abated, estimated in excess of two hundred thousand meteors during the 9 hours of storm, over the entire region of North America east of the Rocky Mountains.
American Denison Olmsted explained the event most accurately. After spending the last weeks of 1833 collecting information, he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, January 1836, he noted the shower was of short duration and was not seen in Europe, that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space. Work continued, yet coming to understand the annual nature of showers though the occurrences of storms perplexed researchers; the actual nature of meteors was still debated during the XIX century. Meteors were conceived as an atmospheric phenomenon by many scientists until the Italian astronomer Giovanni Schiaparelli ascertained the relation between meteors and comets in his work "Notes upon the astronomical theory of the falling stars". In the 1890s, Irish astronomer George Johnstone Stoney and British astronomer Arthur Matthew Weld Downing, were the first to attempt to calculate the position of the dust at Earth's orbit.
They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899. Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earth's orbit; the same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut in Berlin, Germany. Although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of meteor showers for the Leonids and the history of the dynamic orbit of Comet Tempel-Tuttle. A graph from it was re-published in Sky and Telescope, it showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the meteoroids are behind and outside the path of the comet, but paths of the Earth through the cloud of particles resulting in powerful storms were near paths of nearly no activity.
In 1985, E. D. Kondrat'eva and E. A. Reznikov of Kazan State University first identified the years when dust was released, responsible for several past Leonid meteor storms. In 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails. In anticipation of the 1999 Leonid storm, Robert H. McNaught, David Asher, Finland's Esko Lyytinen were the first to apply this method in the West. In 2006 Jenniskens published predictions for future dust trail encounters covering the next 50 years. Jérémie Vaubaillon continues to update predictions based on observations each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides; because meteor shower particles are all traveling in parallel paths, at the same velocity, they will all appear to an observer below to radiate away from a single point in the sky. This radiant point is caused by the effect of perspective, similar to parallel railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks.
Meteor showers are always named after the constellation from which the meteors appear to originate. This "fixed point" moves across the sky during the night due to the Earth turning on its axis, the same reason the stars appear to march across the sky; the radiant moves from night to night against the background stars due to the Earth moving in its orbit around the sun. See IMO Meteor Shower Calendar 2017 for maps of drifting "fixed points." When the moving radiant is at the highest point it will reach in the observer's sky that night, the sun will be just clearing the eastern horizon. For this reason, the best viewing time for a meteor shower is slightly before dawn — a compromise between the maximum number of meteors available for viewing, the lightening sky which makes them harder to see. Meteor showers are named after the nearest constellation or bright star with a Greek or Roman letter assigned, close to the radiant position at the peak of the shower, whereby the grammatical declension of the Latin possessive form is replaced by "id" or "ids".
Hence, meteors radiating from near the star delta Aquarii are called delta Aquariids. The International Astronomical Union's Task Group on Meteor Shower Nomenclature and the IAU's Meteor Data Center keep track of meteor shower nomenclature and which showers are e