1.
September equinox
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An equinox is the moment in which the plane of Earths equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September. On an equinox, day and night are of equal duration all over the planet. They are not exactly equal, however, due to the size of the sun. To avoid this ambiguity, the word equilux is sometimes used to mean a day in which the durations of light, see Length of equinoctial day and night for further discussion. The word is derived from the Latin aequinoctium, aequus and nox, the equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated, the word comes from Latin equi or equal and nox meaning night. In other words, the equinoxes are the times when the subsolar point is on the equator. The subsolar point crosses the equator moving northward at the March equinox, the equinoxes, along with solstices, are directly related to the seasons of the year. In the southern hemisphere, the equinox occurs in September. When Julius Caesar established the Julian calendar in 45 BC, he set 25 March as the date of the spring equinox. Because the Julian year is longer than the tropical year. By 1500 AD, it had drifted backwards to 11 March and this drift induced Pope Gregory XIII to create a modern Gregorian calendar. However, the leap year intervals in his calendar were not smooth and this causes the equinox to oscillate by about 53 hours around its mean position. This in turn raised the possibility that it could fall on 22 March, the astronomers chose the appropriate number of days to omit so that the equinox would swing from 19 to 21 March but never fall on the 22nd. Vernal equinox and Autumnal equinox, these names are direct derivatives of Latin. The equivalent common language English terms spring equinox and autumn equinox are even more ambiguous, March equinox and September equinox, names referring to the months of the year they occur, with no ambiguity as to which hemisphere is the context. They are still not universal, however, as not all use a solar-based calendar where the equinoxes occur every year in the same month. Northward equinox and southward equinox, names referring to the apparent direction of motion of the Sun
2.
Daylight
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Daylight, or the light of day, is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects, sunlight scattered or reflected from objects in outer space is not generally considered daylight. Thus, moonlight is never considered daylight, despite being indirect sunlight, daytime is the period of time each day when daylight occurs. Daylight happens because the Earth rotates and either side the sun shines on is considered daylight, daylight is present at a particular location, to some degree, whenever the sun is above the horizon at that location. It may be darker under unusual circumstances such as an eclipse or very high levels of atmospheric smoke, dust. For comparison, nighttime levels are, For a table of approximate daylight intensity in the Solar System. Daylighting is lighting an indoor space with such as windows. This type of lighting is chosen to save energy, to avoid hypothesized adverse health effects of over-illumination by artificial light, the amount of daylight received into an indoor space or room is defined as a daylight factor, being the ratio between the measured internal and external light levels. In recent years, work has taken place to recreate the effects of daylight artificially and this is however expensive in terms of both equipment and energy consumption and is applied almost exclusively in specialist areas such as filmmaking, where light of such intensity is required anyway. In some filmmaking locations, such as Sweden, there is too much light due to summer days. As a result, in films like Marianne, night scenes have to be shot during the daylight hours. Http, //www. gandraxa. com/length_of_day. xml Deriving the formulas to calculate the length of day
3.
Equinox
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An equinox is the moment in which the plane of Earths equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September. On an equinox, day and night are of equal duration all over the planet. They are not exactly equal, however, due to the size of the sun. To avoid this ambiguity, the word equilux is sometimes used to mean a day in which the durations of light, see Length of equinoctial day and night for further discussion. The word is derived from the Latin aequinoctium, aequus and nox, the equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated, the word comes from Latin equi or equal and nox meaning night. In other words, the equinoxes are the times when the subsolar point is on the equator. The subsolar point crosses the equator moving northward at the March equinox, the equinoxes, along with solstices, are directly related to the seasons of the year. In the southern hemisphere, the equinox occurs in September. When Julius Caesar established the Julian calendar in 45 BC, he set 25 March as the date of the spring equinox. Because the Julian year is longer than the tropical year. By 1500 AD, it had drifted backwards to 11 March and this drift induced Pope Gregory XIII to create a modern Gregorian calendar. However, the leap year intervals in his calendar were not smooth and this causes the equinox to oscillate by about 53 hours around its mean position. This in turn raised the possibility that it could fall on 22 March, the astronomers chose the appropriate number of days to omit so that the equinox would swing from 19 to 21 March but never fall on the 22nd. Vernal equinox and Autumnal equinox, these names are direct derivatives of Latin. The equivalent common language English terms spring equinox and autumn equinox are even more ambiguous, March equinox and September equinox, names referring to the months of the year they occur, with no ambiguity as to which hemisphere is the context. They are still not universal, however, as not all use a solar-based calendar where the equinoxes occur every year in the same month. Northward equinox and southward equinox, names referring to the apparent direction of motion of the Sun
4.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
5.
Southern Hemisphere
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The Southern Hemisphere is the half sphere of Earth which is south of the equator. It contains all or parts of five continents, four oceans and its surface is 80. 9% water, compared with 60. 7% water in the case of the Northern Hemisphere, and it contains 32. 7% of Earths land. Due to the tilt of Earths rotation relative to the Sun, September 22 or 23 is the vernal equinox and March 20 or 21 is the autumnal equinox. The South Pole is in the middle of the southern hemispherical region, Southern Hemisphere climates tend to be slightly milder than those at similar latitudes in the Northern Hemisphere, except in the Antarctic which is colder than the Arctic. This is because the Southern Hemisphere has significantly more ocean and much land, water heats up. In the Southern Hemisphere the sun passes from east to west through the north, sun-cast shadows turn anticlockwise throughout the day and sundials have the hours increasing in the anticlockwise direction. 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. Forests in the Southern Hemisphere have special features which set apart from those in the Northern Hemisphere. Both Chile and Australia share, for example, unique species or Nothofagus. The eucalyptus is native to Australia but is now planted in Southern Africa and Latin America for pulp production and, increasingly. Approximately 800,000,000 humans live in the Southern Hemisphere and this is due to the fact that there is significantly less land in the Southern Hemisphere than in the Northern Hemisphere. Africa Antarctica Asia Australia South America Zealandia Media related to Southern Hemisphere at Wikimedia Commons
6.
Celestial equator
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The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earths equator. In other words, it is a projection of the terrestrial equator out into space, as a result of the Earths axial tilt, the celestial equator is inclined by 23. 4° with respect to the ecliptic plane. An observer standing on the Earths equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith, as the observer moves north, the celestial equator tilts towards the opposite horizon. Celestial objects near the equator are visible worldwide, but they culminate the highest in the sky in the tropics. The celestial equator currently passes through these constellations, Celestial bodies other than Earth also have similarly defined celestial equators, Celestial pole Celestial sphere Declination Equatorial coordinate system
7.
Northern Hemisphere
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The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the celestial hemisphere relative to the invariable plane of the solar system as Earths North pole. Due to the Earths axial tilt, winter in the Northern Hemisphere lasts from the December solstice to the March Equinox, the dates vary each year due to the difference between the calendar year and the astronomical year. Its surface is 60. 7% water, compared with 80. 9% water in the case of the Southern Hemisphere, the Arctic is the region north of the Arctic Circle. Its climate is characterized by cold winters and cool summers, precipitation mostly comes in the form of snow. The Arctic experiences some days in summer when the Sun never sets, the duration of these phases varies from one day for locations right on the Arctic Circle to several months near the North Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer lies the Northern Temperate Zone, the changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather, tropical regions are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during the winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the coriolis effect, as a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres. These are best seen in circulation patterns in the North Atlantic. For the same reason, flows of air down toward the surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere, conversely, air rising from the northern surface of the Earth tends to draw air toward it in a counterclockwise pattern. Hurricanes and tropical storms spin counter-clockwise in the Northern Hemisphere, the shadow of a sundial moves clockwise in the Northern Hemisphere. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere, the North Pole faces away from the galactic center of the Milky Way. The Northern Hemisphere is home to approximately 6.57 billion people which is around 90% of the total human population of 7.3 billion people
8.
Gregorian calendar
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The Gregorian calendar is internationally the most widely used civil calendar. It is named after Pope Gregory XIII, who introduced it in October 1582, the calendar was a refinement to the Julian calendar involving a 0. 002% correction in the length of the year. The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices—particularly the northern vernal equinox, transition to the Gregorian calendar would restore the holiday to the time of the year in which it was celebrated when introduced by the early Church. The reform was adopted initially by the Catholic countries of Europe, the last European country to adopt the reform was Greece, in 1923. Many countries that have used the Islamic and other religious calendars have come to adopt this calendar for civil purposes. The reform was a modification of a made by Aloysius Lilius. His proposal included reducing the number of years in four centuries from 100 to 97. Lilius also produced an original and practical scheme for adjusting the epacts of the moon when calculating the date of Easter. For example, the years 1700,1800, and 1900 are not leap years, but the years 1600 and 2000 are. The canonical Easter tables were devised at the end of the third century, when the vernal equinox fell either on 20 March or 21 March depending on the years position in the leap year cycle. As the rule was that the full moon preceding Easter was not to precede the equinox, the date was fixed at 21 March for computational purposes, the Gregorian calendar reproduced these conditions by removing ten days. To unambiguously specify a date, dual dating or Old Style, dual dating gives two consecutive years for a given date, because of differences in the starting date of the year, and/or to give both the Julian and the Gregorian dates. The Gregorian calendar continued to use the calendar era, which counts years from the traditional date of the nativity. This year-numbering system, also known as Dionysian era or Common Era, is the predominant international standard today, the Gregorian calendar is a solar calendar. A regular Gregorian year consists of 365 days, but as in the Julian calendar, in a leap year, in the Julian calendar a leap year occurs every 4 years, but the Gregorian calendar omits 3 leap days every 400 years. In the Julian calendar, this day was inserted by doubling 24 February. In the modern period, it has become customary to number the days from the beginning of the month, some churches, notably the Roman Catholic Church, delay February festivals after the 23rd by one day in leap years. Gregorian years are identified by consecutive year numbers, the cycles repeat completely every 146,097 days, which equals 400 years
9.
Spring (season)
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Spring is one of the four conventional temperate seasons, following winter and preceding summer. There are various definitions of spring, but local usage of the term varies according to local climate, cultures. When it is spring in the Northern Hemisphere, it will be autumn in the Southern Hemisphere, at the spring equinox, days are approximately 12 hours long with day length increasing as the season progresses. Spring and springtime refer to the season, and also to ideas of rebirth, rejuvenation, renewal, resurrection, subtropical and tropical areas have climates better described in terms of other seasons, e. g. dry or wet, monsoonal or cyclonic. Often, cultures have locally defined names for seasons which have little equivalence to the terms originating in Europe, Spring is the time when many plants begin to grow and flower. Meteorologists generally define four seasons in many areas, spring, summer, autumn. These are demarcated by the values of their average temperatures on a monthly basis, 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, in most Northern Hemisphere, temperate locations, spring months are March, April and May, although differences exist from country to country. Most Southern Hemisphere, temperate locations have opposing seasons with spring in September, October and November, in Australia and New Zealand, spring conventionally begins on 1 September and ends 30 November. In some cultures in the Northern Hemisphere, the astronomical Vernal equinox is taken to mark the first day of spring, 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, similarly, according to the Celtic tradition, which is based solely on daylight and the strength of the noon sun, spring begins in early February and continues until early May. In Ireland, spring traditionally starts on February 1, St Brigids Day, the beginning of spring is not always determined by fixed calendar dates. These indicators, along with the beginning of spring, vary according to the local climate, most ecologists divide the year into six seasons that have no fixed dates. In addition to spring, ecological reckoning identifies an earlier separate prevernal season between the hibernal and vernal seasons and 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 hemisphere begins to warm significantly, 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, and rare frosts, air and ground temperatures increase more rapidly. Many flowering plants bloom at this time of year, in a succession, sometimes beginning when snow is still on the ground. In normally snowless areas, spring may begin as early as February, heralded by the blooming of deciduous magnolias, cherries, and quince, or August in the same way
10.
Winter
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Winter is the coldest season of the year in polar and temperate climates, between autumn and spring. Winter is caused by the axis of the Earth in that hemisphere being oriented away from the Sun, different cultures define different dates as the start of winter, and some use a definition based on weather. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, in many regions, winter is associated with snow and freezing temperatures. The moment of winter solstice is when the elevation with respect to the North or South Pole is at its most negative value, meaning this day will have the shortest day. The English word winter comes from the Proto-Indo-European root wend, relating to water, the tilt of the Earths axis relative to its orbital plane plays a large role in the formation of weather. The Earth is tilted at an angle of 23. 44° to the plane of its orbit, when it is winter in the Northern Hemisphere, the Southern Hemisphere faces the Sun more directly and thus experiences warmer temperatures than the Northern Hemisphere. Conversely, winter in the Southern Hemisphere occurs when the Northern Hemisphere is tilted more toward the Sun, from the perspective of an observer on the Earth, the winter Sun has a lower maximum altitude in the sky than the summer Sun. During winter in either hemisphere, the altitude of the Sun causes the sunlight to hit that hemisphere at an oblique angle. In regions experiencing winter, the amount of solar radiation is spread out over a larger area. This effect is compounded by the distance that the light must travel through the atmosphere. Compared with these effects, the changes in the distance of the earth from the sun are negligible, the manifestation of the meteorological winter in the northerly snow–prone parallels is highly variable depending on elevation, position versus marine winds and the amount of precipitation. A case in point is Canada, a country associated with tough winters. Winnipeg on the Great Plains at a distance from large bodies of water has a January high of −11.3 °C. In comparison, Vancouver on the coast with an influence from moderating Pacific winds has a January low of 1.4 °C with days well above freezing at 6.9 °C. Both areas are on the 49th parallel north and in the western half of the continent. Winter is often defined by meteorologists to be the three months with the lowest average temperatures. This corresponds to the months of December, January and February in the Northern Hemisphere, the coldest average temperatures of the season are typically experienced in January or February in the Northern Hemisphere and in June, July or August in the Southern Hemisphere. Blizzards often develop and cause many transportation delays, diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40 °F due to air with slightly higher moisture from aloft mixing with colder, surface based air
11.
Autumn
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Autumn, also known as fall in North American English, is one of the four temperate seasons. One of its features is the shedding of leaves from deciduous trees. Some cultures regard the autumnal equinox as mid-autumn, while others with a longer temperature lag treat it as the start of autumn. Meteorologists use a definition based on months, with autumn being September, October and November in the northern hemisphere, in North America, autumn is usually considered to start with the September equinox and end with the winter solstice. As daytime and nighttime temperatures decrease, trees shed their leaves, in traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the meteorological service. In Australia and New Zealand, autumn officially begins on 1 March, the word autumn comes from the ancient Etruscan root autu- and has within it connotations of the passing of the year. It was borrowed by the neighbouring Romans, and became the Latin word autumnus, after the Roman era, the word continued to be used as the Old French word autompne or autumpne in Middle English, and was later normalized to the original Latin. In the Medieval period, there are examples of its use as early as the 12th century. Before the 16th century, harvest was the usually used to refer to the season. The alternative word fall for the season traces its origins to old Germanic languages, the exact derivation is unclear, with the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these all have the meaning to fall from a height and are clearly derived either from a common root or from each other. The term came to denote the season in 16th century England, during the 17th century, English emigration to the British colonies in North America was at its peak, and the new settlers took the English language with them. While the term gradually became obsolete in Britain, it became the more common term in North America. The name backend, a common name for the season in Northern England, has today been largely replaced by the name autumn. Association with the transition from warm to cold weather, and its status as the season of the primary harvest, has dominated its themes. In Western cultures, personifications of autumn are usually pretty, well-fed females adorned with fruits, vegetables, many cultures feature autumnal harvest festivals, often the most important on their calendars. There are also the many North American Indian festivals tied to harvest of ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, and many others
12.
Summer
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Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, the date of the beginning of summer varies according to climate, tradition and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, a variable seasonal lag means that the meteorological center of the season, which is based on average temperature patterns, occurs several weeks after the time of maximal insolation. Under meteorological definitions, all seasons are set to start at the beginning of a calendar month. This meteorological definition of summer also aligns with the commonly viewed notion of summer as the season with the longest days of the year, the meteorological reckoning of seasons is used in Australia, Austria, Denmark, the former Soviet Union and Japan. It is also used by many in the United Kingdom, in Ireland, the summer months according to the national meteorological service, Met Éireann, are June, July and August. However, according to the Irish Calendar, summer begins on 1 May, school textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June. Reckoning by hours of daylight alone, summer solstice marks the midpoint, not the beginning, midsummer takes place over the shortest night of the year, which is the summer solstice, or on a nearby date that varies with tradition. Where a seasonal lag of half a season or more is common, by this method, in North America, summer is the period from the summer solstice to the autumn equinox. The similar Canadian tradition starts summer on Victoria Day one week prior and ends, as in the United States, on Labour Day. In Chinese astronomy, summer starts on or around 5 May, with the known as lìxià, i. e. establishment of summer. In Australia and New Zealand, summer begins on 1 December. Summer is traditionally associated with hot or warm weather, in the Mediterranean regions, it is also associated with dry weather, while in other places it is associated with rainy weather. The wet season is the period of vegetation growth within the savanna climate regime. Where the wet season is associated with a shift in the prevailing winds. In the northern Atlantic Ocean, a tropical cyclone season occurs from 1 June to 30 November. The statistical peak of the Atlantic hurricane season is 10 September, the Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March, in the North Indian basin, storms are most common from April to December, with peaks in May and November
13.
Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, 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 the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually 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, and the nature of the Sun, Moon, 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 model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
14.
Sidereal time
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Sidereal time /saɪˈdɪəriəl/ is a time-keeping system that astronomers use to locate celestial objects. Using sidereal time it is possible to point a telescope to the proper coordinates in the night sky. Briefly, sidereal time is a scale that is based on Earths rate of rotation measured relative to the fixed stars rather than the Sun. From a given point, a star found at one location in the sky will be found at the same location on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun, just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earths rotation about its polar axis, a mean sidereal day is 23 hours,56 minutes,4.0916 seconds, the time it takes Earth to make one rotation relative to the vernal equinox. The longer true sidereal period is called a day by the International Earth Rotation. It is also referred to as the period of rotation. Maps of the stars in the night sky use declination and right ascension as coordinates and these correspond to latitude and longitude respectively. In the sky, the meridian is the north to south line that goes through the point directly overhead. Solar time is measured by the apparent diurnal motion of the Sun, a mean solar day is the average time between local solar noons. Earth makes one rotation around its axis in a sidereal day, so after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day, the stars are so far away that Earths movement along its orbit makes nearly no difference to their apparent direction, and so they return to their highest point in a sidereal day. Another way to see this difference is to notice that, relative to the stars, therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately 365. 24/366.24 times the length of the 24-hour solar day, Earths rotation is not a simple rotation around an axis that would always remain parallel to itself. Earths rotational axis itself rotates about an axis, orthogonal to Earths orbit. This phenomenon is called the precession of the equinoxes, because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation. In this reference frame, Earths rotation is close to constant and it is also in this reference frame that the tropical year, the year related to Earths seasons, represents one orbit of Earth around the Sun
15.
Right ascension
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Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question. When combined with declination, these astronomical coordinates specify the direction of a point on the sphere in the equatorial coordinate system. Right ascension is the equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a direction on an equator. Right ascension is measured continuously in a circle from that equinox towards the east. Any units of measure could have been chosen for right ascension, but it is customarily measured in hours, minutes. Astronomers have chosen this unit to measure right ascension because they measure a stars location by timing its passage through the highest point in the sky as the Earth rotates. The highest point in the sky, called meridian, is the projection of a line onto the celestial sphere. A full circle, measured in units, contains 24 × 60 × 60 = 86 400s, or 24 × 60 = 1 440m. Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 01h 30m 00s is on the meridian, sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Usually measured in degrees, it is the complement of right ascension with respect to 24h and it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earths axis rotates slowly westward about the poles of the ecliptic and this effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. The right ascension of Polaris is increasing quickly, the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC. But Hipparchus and his successors made their star catalogs in ecliptic coordinates, the easiest way to do that is to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earths axis
16.
Axial precession
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In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical bodys rotational axis. The term precession typically refers only to this largest part of the motion, other changes in the alignment of Earths axis—nutation and this term is still used in non-technical discussions, that is, when detailed mathematics are absent. Their combination was named general precession, instead of precession of the equinoxes, lunisolar precession is caused by the gravitational forces of the Moon and Sun on Earths equatorial bulge, causing Earths axis to move with respect to inertial space. Lunisolar precession is about 500 times greater than planetary precession, many references to the old terms exist in publications predating the change. Etymologically, precession and procession are both terms that relate to motion, Precession is derived from the Latin praecedere, to precede, to come before or earlier), while procession is derived from the Latin procedere, to march forward, to advance). Generally the term procession is used to describe a group of objects moving forward, the stars viewed from Earth are seen to proceed in a procession from east to west daily, due to the Earth’s diurnal motion, and yearly, due to the Earth’s revolution around the Sun. At the same time the stars can be observed to anticipate slightly such motion, at the rate of approximately 50 arc seconds per year, in describing this motion astronomers generally have shortened the term to simply precession. This issue is further obfuscated by the fact that many astronomers are physicists or astrophysicists, the precession of the Earths axis has a number of observable effects. First, the positions of the south and north celestial poles appear to move in circles against the backdrop of stars. Thus, while today the star Polaris lies approximately at the celestial pole, this will change over time. In approximately 3200 years, the star Gamma Cephei in the Cepheus constellation will succeed Polaris for this position, the south celestial pole currently lacks a bright star to mark its position, but over time precession also will cause bright stars to become south stars. As the celestial poles shift, there is a gradual shift in the apparent orientation of the whole star field. Secondly, the position of the Earth in its orbit around the Sun at the solstices, equinoxes, or other time defined relative to the seasons, slowly changes. For example, suppose that the Earths orbital position is marked at the summer solstice, in other words, the solstice occurred a little earlier in the orbit. Thus, the year, measuring the cycle of seasons, is about 20 minutes shorter than the sidereal year. For further details, see Changing pole stars and Polar shift and equinoxes shift, according to Ptolemys Almagest, Hipparchus measured the longitude of Spica and other bright stars. Comparing his measurements with data from his predecessors, Timocharis and Aristillus and he also compared the lengths of the tropical year and the sidereal year, and found a slight discrepancy. Virtually all of the writings of Hipparchus are lost, including his work on precession and they are mentioned by Ptolemy, who explains precession as the rotation of the celestial sphere around a motionless Earth
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Constellation
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A constellation is formally defined as a region of the celestial sphere, with boundaries laid down by the International Astronomical Union. The constellation areas mostly had their origins in Western-traditional patterns of stars from which the constellations take their names, in 1922, the International Astronomical Union officially recognized the 88 modern constellations, which cover the entire sky. They began as the 48 classical Greek constellations laid down by Ptolemy in the Almagest, Constellations in the far southern sky are late 16th- and mid 18th-century constructions. 12 of the 88 constellations compose the zodiac signs, though the positions of the constellations only loosely match the dates assigned to them in astrology. The term constellation can refer to the stars within the boundaries of that constellation. Notable groupings of stars that do not form a constellation are called asterisms, when astronomers say something is “in” a given constellation they mean it is within those official boundaries. Any given point in a coordinate system can unambiguously be assigned to a single constellation. Many astronomical naming systems give the constellation in which an object is found along with a designation in order to convey a rough idea in which part of the sky it is located. For example, the Flamsteed designation for bright stars consists of a number, the word constellation seems to come from the Late Latin term cōnstellātiō, which can be translated as set of stars, and came into use in English during the 14th century. It also denotes 88 named groups of stars in the shape of stellar-patterns, the Ancient Greek word for constellation was ἄστρον. Colloquial usage does not draw a distinction between constellation in the sense of an asterism and constellation in the sense of an area surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept, the term circumpolar constellation is used for any constellation that, from a particular latitude on Earth, never sets below the horizon. From the North Pole or South Pole, all constellations south or north of the equator are circumpolar constellations. In the equatorial or temperate latitudes, the term equatorial constellation has sometimes been used for constellations that lie to the opposite the circumpolar constellations. They generally include all constellations that intersect the celestial equator or part of the zodiac, usually the only thing the stars in a constellation have in common is that they appear near each other in the sky when viewed from the Earth. In galactic space, the stars of a constellation usually lie at a variety of distances, since stars also travel on their own orbits through the Milky Way, the star patterns of the constellations change slowly over time. After tens to hundreds of thousands of years, their familiar outlines will become unrecognisable, the terms chosen for the constellation themselves, together with the appearance of a constellation, may reveal where and when its constellation makers lived. The earliest direct evidence for the constellations comes from inscribed stones and it seems that the bulk of the Mesopotamian constellations were created within a relatively short interval from around 1300 to 1000 BC
18.
Aries (constellation)
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Aries is one of the constellations of the zodiac. It is located in the celestial hemisphere between Pisces to the west and Taurus to the east. The name Aries is Latin for ram, and its symbol is and it is one of the 48 constellations described by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations. It is a constellation, ranking 39th overall size, with an area of 441 square degrees. Although Aries came to represent specifically the ram whose fleece became the Golden Fleece of Ancient Greek mythology, before that, the stars of Aries formed a farmhand. Different cultures have incorporated the stars of Aries into different constellations including twin inspectors in China, Aries is a relatively dim constellation, possessing only four bright stars, Hamal, Sheratan, Mesarthim, and 41 Arietis. The few deep-sky objects within the constellation are faint and include several pairs of interacting galaxies. Several meteor showers appear to radiate from Aries, including the Daytime Arietids, Aries is now recognized as an official constellation, albeit as a specific region of the sky, by the International Astronomical Union. It was originally defined in ancient texts as a pattern of stars. In the description of the Babylonian zodiac given in the clay tablets known as the MUL. APIN, the MUL. APIN was a comprehensive table of the risings and settings of stars, which likely served as an agricultural calendar. Modern-day Aries was known as MULLÚ. ḪUN. GÁ, The Agrarian Worker or The Hired Man, the earliest identifiable reference to Aries as a distinct constellation comes from the boundary stones that date from 1350 to 1000 BC. On several boundary stones, a zodiacal ram figure is distinct from the characters present. The shift in identification from the constellation as the Agrarian Worker to the Ram likely occurred in later Babylonian tradition because of its association with Dumuzi the Shepherd. By the time the MUL. APIN was created—by 1000 BC—modern Aries was identified with both Dumuzis ram and a hired laborer, the exact timing of this shift is difficult to determine due to the lack of images of Aries or other ram figures. In ancient Egyptian astronomy, Aries was associated with the god Amon-Ra, because it was the location of the vernal equinox, it was called the Indicator of the Reborn Sun. During the times of the year when Aries was prominent, priests would process statues of Amon-Ra to temples, Aries acquired the title of Lord of the Head in Egypt, referring to its symbolic and mythological importance. Aries was not fully accepted as a constellation until classical times, in Hellenistic astrology, the constellation of Aries is associated with the golden ram of Greek mythology that rescued Phrixos and Helle on orders from Hermes, taking Phrixos to the land of Colchis. Phrixos and Helle were the son and daughter of King Athamas, the kings second wife, Ino, was jealous and wished to kill his children
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Pisces (constellation)
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Pisces is a constellation of the zodiac. Its name is the Latin plural for fish and it lies between Aquarius to the west and Aries to the east. The ecliptic and the equator intersect within this constellation and in Virgo. The vernal equinox is currently located in Pisces, due south of ω Psc, van Maanens Star, at 12.36 magnitude, is located in this constellation, along with others, such as HD222410, at 7.45 magnitude. It has many clusters of stars and the associated nebulae. It was discovered by Pierre Méchain, a French astronomer, in 1780, NGC488 is an isolated face-on prototypical spiral galaxy. NGC520 is a pair of colliding galaxies located 90 million lightyears away, CL 0024+1654 is a massive galaxy cluster that lenses the galaxy behind it, creating arc-shaped images of the background galaxy. 3C31 is a galaxy and radio source in Perseus located at a distance of 237 million light-years from Earth. Its jets, caused by the black hole at its center. Pisces originates from some composition of the Babylonian constellations Šinunutu4 the great swallow in current western Pisces, in the first-millennium BC texts known as the Astronomical Diaries, part of the constellation was also called DU. NU. NU. Pisces is associated with Aphrodite and Eros, who escaped from the monster Typhon by leaping into the sea, in order not to lose each other, they tied themselves together with rope. The Romans adopted the Greek legend, with Venus and Cupid acting as the counterparts for Aphrodite, the knot of the rope is marked by Alpha Piscium, also called Al-Rischa. Linum Boreum, χ – ρ,94 – VX – η – π – ο – α Psc, linum Austrinum, α – ξ – ν – μ – ζ – ε – δ –41 –35 – ω Psc. Piscis Austrinus, ω – ι – θ –7 – β –5 – κ,9 – λ – TX Psc. However the proposal was largely neglected by other astronomers with the exception of Admiral Smyth, who mentioned it in his book The Bedford Catalogue, and it is now obsolete. The Fishes are also associated with the German legend of Antenteh, who owned just a tub and they offered him a wish, which he refused. However, his wife begged him to return to the fish and this wish was granted, but her desires were not satisfied. She then asked to be a queen and have a palace, but when she asked to become a goddess, the tub in the story is sometimes recognized as the Great Square of Pegasus
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Aquarius (constellation)
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Aquarius is a constellation of the zodiac, situated between Capricornus and Pisces. Its name is Latin for water-carrier or cup-carrier, and its symbol is, Aquarius is one of the oldest of the recognized constellations along the zodiac. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and it is found in a region often called the Sea due to its profusion of constellations with watery associations such as Cetus the whale, Pisces the fish, and Eridanus the river. At apparent magnitude 2.9, Beta Aquarii is the brightest star in the constellation, Aquarius is identified as GU. LA The Great One in the Babylonian star catalogues and represents the god Ea himself, who is commonly depicted holding an overflowing vase. The Babylonian star-figure appears on entitlement stones and cylinder seals from the second millennium and it contained the winter solstice in the Early Bronze Age. In Old Babylonian astronomy, Ea was the ruler of the southernmost quarter of the Suns path, Aquarius was also associated with the destructive floods that the Babylonians regularly experienced, and thus was negatively connoted. In Ancient Egypt astronomy, Aquarius was associated with the flood of the Nile. In the Greek tradition, the constellation came to be represented simply as a vase from which a stream poured down to Piscis Austrinus. The name in the Hindu zodiac is likewise kumbha water-pitcher, in Greek mythology, Aquarius is sometimes associated with Deucalion, the son of Prometheus who built a ship with his wife Pyrrha to survive an imminent flood. They sailed for nine days before washing ashore on Mount Parnassus, Aquarius is also sometimes identified with beautiful Ganymede, a youth in Greek mythology and the son of Trojan king Tros, who was taken to Mount Olympus by Zeus to act as cup-carrier to the gods. Neighboring Aquila represents the eagle, under Zeus command, that snatched the young boy, yet another figure associated with the water bearer is Cecrops I, a king of Athens who sacrificed water instead of wine to the gods. In the first century, Ptolemys Almagest established the common Western depiction of Aquarius. His water jar, an asterism itself, consists of Gamma, Pi, Eta, the water bearers head is represented by 5th magnitude 25 Aquarii while his left shoulder is Beta Aquarii, his right shoulder and forearm are represented by Alpha and Gamma Aquarii respectively. In Chinese astronomy, the stream of flowing from the Water Jar was depicted as the Army of Yu-Lin. The name Yu-lin means feathers and forests, referring to the numerous light-footed soldiers from the reaches of the empire represented by these faint stars. The constellations stars were the most numerous of any Chinese constellation, numbering 45, the celestial army was protected by the wall Leibizhen, which counted Iota, Lambda, Phi, and Sigma Aquarii among its 12 stars. 88,89, and 98 Aquarii represent Fou-youe, the used as weapons. Also in Aquarius is Loui-pi-tchin, the ramparts that stretch from 29 and 27 Piscium and 33 and 30 Aquarii through Phi, Lambda, Sigma, and Iota Aquarii to Delta, Gamma, Kappa, and Epsilon Capricorni
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88 modern constellations
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In modern astronomy, the sky is divided into 88 regions called constellations, generally based on the asterisms of Greek and Roman mythology. Those along the ecliptic are the constellations of the zodiac, the ancient Sumerians, and later the Greeks, established most of the northern constellations in international use today. Not all of these proposals caught on, but in 1922, after this, Eugène Joseph Delporte drew up precise boundaries for each constellation, so that every point in the sky belonged to exactly one constellation. Some constellations are no longer recognized by the International Astronomical Union, most notable is Argo Navis, which was one of Ptolemys original 48 constellations. The 88 constellations depict 42 animals,29 inanimate objects and 17 humans or mythological characters, each of the IAU constellations has an official 3 letter abbreviation. They are actually abbreviations of the form of the constellation names. The majority of the abbreviations are just the first three letters of the constellation, with the first character capitalised, Ori for Orion, Ara for Ara/Arae, Com for Coma Berenices. When letters are taken from the word of a two-word name. The abbreviations are unambiguous, with two exceptions, Leo for the constellation Leo could be mistaken for Leo Minor, and Tri for Triangulum could be mistaken for Triangulum Australe. For help with the literary English pronunciations, see the pronunciation key, there is considerable diversity in how Latinate names are pronounced in English. For traditions closer to the original, see Latin spelling and pronunciation, the Family column refers to the constellation families introduced by Donald Menzel in 1975. Various other unofficial patterns have existed alongside the constellations, examples include the Big Dipper/Plough and the Northern Cross. Some ancient asterisms, for example Coma Berenices, Serpens, http, //www. ianridpath. com/startales/contents. htm – Ian Ridpaths Star Tales. Http, //cdsarc. u-strasbg. fr/viz-bin/Cat. cat=VI/49 – CDSs archive of constellation boundaries, the text file constbnd. dat gives the 1875.0 coordinates of the vertices of the constellation regions, together with the constellations adjacent to each boundary segment
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Taurus (constellation)
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Taurus is one of the constellations of the zodiac, which means it is crossed by the plane of the ecliptic. Taurus is a large and prominent constellation in the northern hemispheres winter sky and it is one of the oldest constellations, dating back to at least the Early Bronze Age when it marked the location of the Sun during the spring equinox. Its importance to the agricultural calendar influenced various bull figures in the mythologies of Ancient Sumer, Akkad, Assyria, Babylon, Egypt, Greece, a number of features exist that are of interest to astronomers. Taurus hosts two of the nearest open clusters to Earth, the Pleiades and the Hyades, both of which are visible to the naked eye, at first magnitude, the red giant Aldebaran is the brightest star in the constellation. In the northwest part of Taurus is the supernova remnant Messier 1, one of the closest regions of active star formation, the Taurus-Auriga complex, crosses into the northern part of the constellation. The variable star T Tauri is the prototype of a class of pre-main-sequence stars, in September and October, Taurus is visible in the evening along the eastern horizon. The most favorable time to observe Taurus in the sky is during the months of December. By March and April, the constellation will appear to the west during the evening twilight and this constellation forms part of the zodiac, and hence is intersected by the ecliptic. This circle across the sphere forms the apparent path of the Sun as the Earth completes its annual orbit. As the orbital plane of the Moon and the planets lie near the ecliptic, the galactic plane of the Milky Way intersects the northeast corner of the constellation and the galactic anticenter is located near the border between Taurus and Auriga. Taurus is the only constellation crossed by all three of the equator, celestial equator, and ecliptic. A ring-like galactic structure known as the Goulds Belt passes through the Taurus constellation, the recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is Tau. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 26 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 03h 23. 4m and 05h 53. 3m, while the coordinates are between 31. 10° and −1. 35°. Because a small part of the lies to the south of the celestial equator. During November, the Taurid meteor shower appears to radiate from the direction of this constellation. The Beta Taurid meteor shower occurs during the months of June and July in the daytime, between 18 and 29 October, both the Northern Taurids and the Southern Taurids are active, though the latter stream is stronger. However, between November 1 and 10, the two streams equalize, the brightest member of this constellation is Aldebaran, an orange-hued, spectral class K5 III giant star
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Capricornus
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Capricornus /ˌkæprᵻˈkɔːrnəs/ is one of the constellations of the zodiac. Its name is Latin for horned goat or goat horn or having horns like a goats, and it is represented in the form of a sea-goat. Capricornus is one of the 88 modern constellations, and was one of the 48 constellations listed by the 2nd century astronomer Ptolemy. Under its modern boundaries it is bordered by Aquila, Sagittarius, Microscopium, Piscis Austrinus, the constellation is located in an area of sky called the Sea or the Water, consisting of many water-related constellations such as Aquarius, Pisces and Eridanus. It is the smallest constellation in the zodiac, Capricornus is a faint constellation, with only one star above magnitude 3, its alpha star has a magnitude of only 3.6. The brightest star in Capricornus is δ Capricorni, also called Deneb Algedi, like several other stars such as Denebola and Deneb, it is named for the Arabic word for tail, its traditional name means the tail of the goat. Deneb Algedi is a Beta Lyrae variable star and it ranges by about 0.2 magnitudes with a period of 24.5 hours. The other bright stars in Capricornus range in magnitude from 3.1 to 5.1, α Capricorni is a multiple star also known as Algedi or Giedi. The primary,109 light-years from Earth, is a giant star of magnitude 3.6. The secondary,690 light-years from Earth, is a supergiant star of magnitude 4.3. The two stars are distinguishable by the eye, and both are themselves multiple stars. α1 Capricorni is accompanied by a star of magnitude 9.2, α2 Capricornus is accompanied by a star of magnitude 11.0, the traditional names of α Capricorni come from the Arabic word for the kid, which references the constellations mythology. β Capricorni is a double star also known as Dabih and it is a yellow-hued giant star of magnitude 3.1,340 light-years from Earth. The secondary is a blue-white hued star of magnitude 6.1, the two stars are distinguishable in binoculars. β Capricornis traditional name comes from the Arabic phrase for the stars of the slaughterer. Another star visible to the eye is γ Capricorni, sometimes called Nashira. π Capricorni is a star with a blue-white hued primary of magnitude 5.1. It is 670 light-years from Earth and the components are distinguishable in a small telescope, several galaxies and star clusters are contained within Capricornus
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Cetus
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Its name refers to Cetus, a sea monster in Greek mythology, although it is often called the whale today. Cetus is located in the region of the sky that contains other water-related constellations such as Aquarius, Pisces and this is all the more true of asteroids, since their orbits usually have a greater inclination to the ecliptic than the moon and planets. For example, the asteroid 4 Vesta was discovered in this constellation in 1807, as seen from Mars, the ecliptic passes into Cetus, with the sun appearing in Cetus for around six days shortly after the northern summer solstice. Marss orbit is tilted by 1. 85° with respect to Earths, Mira, designated Omicron Ceti, was the first variable star to be discovered and the prototype of its class. Over a period of 332 days it reaches an apparent magnitude of 3 - visible to the naked eye - and dips to a minimum magnitude of 10. Its seeming appearance and disappearance gave it its name, which means the amazing one. Mira pulsates with a size of 400 solar diameters and a maximum size of 500 solar diameters. 420 light-years from Earth, it was discovered by David Fabricius in 1596, α Ceti, traditionally called Menkar, is a red-hued giant star of magnitude 2.5,220 light-years from Earth. It is a double star, the secondary is 93 Ceti. β Ceti, also called Deneb Kaitos and Diphda, is the brightest star in Cetus and it is an orange-hued giant star of magnitude 2.0,96 light-years from Earth. The traditional name Deneb Kaitos means the whales tail, γ Ceti, Kaffaljidhma is a very close double star. The primary is a star of magnitude 3.5,82 light-years from Earth. Tau Ceti is noted for being the nearest Sun-like star at a distance of 11.9 light-years and it is a yellow-hued main-sequence star of magnitude 3.5. AA Ceti is a star system, the brightest member has a magnitude of 6.2. The primary and secondary are separated by 8.4 arcseconds at an angle of 304 degrees, the tertiary is not visible in telescopes. AA Ceti is a variable star, the tertiary star passes in front of the primary. UV Ceti is a binary variable star. 8.7 light-years from Earth, the system consists of two red dwarfs, one of the stars is a flare star, which are prone to sudden, random outbursts that last several minutes, these increase the pairs apparent brightness significantly - as high as magnitude 7
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Refraction
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Refraction is the change in direction of wave propagation due to a change in its transmission medium. The phenomenon is explained by the conservation of energy and the conservation of momentum, due to the change of medium, the phase velocity of the wave is changed but its frequency remains constant. This is most commonly observed when a wave passes from one medium to another at any other than 0° from the normal. In optics, refraction is a phenomenon that occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle. At the boundary between the media, the phase velocity is altered, usually causing a change in direction. Its wavelength increases or decreases, but its frequency remains constant, for example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index. A ray traveling along the normal will change speed, but not direction, refraction still occurs in this case. Understanding of this led to the invention of lenses and the refracting telescope. Refraction can be seen looking into a bowl of water. Air has a index of about 1.0003. If a person looks at an object, such as a pencil or straw, which is placed at a slant, partially in the water. This is due to the bending of light rays as they move from the water to the air, once the rays reach the eye, the eye traces them back as straight lines. The lines of sight intersect at a position than where the actual rays originated. This causes the pencil to appear higher and the water to appear shallower than it really is, the depth that the water appears to be when viewed from above is known as the apparent depth. This is an important consideration for spearfishing from the surface because it will make the fish appear to be in a different place. Conversely, an object above the water has a higher apparent height when viewed from below the water, the opposite correction must be made by an archer fish. For small angles of incidence, the ratio of apparent to real depth is the ratio of the indexes of air to that of water. But, as the angle of incidence approaches 90o, the apparent depth approaches zero, albeit reflection increases, the diagram on the right shows an example of refraction in water waves
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Declination
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In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declinations angle is measured north or south of the celestial equator, the root of the word declination means a bending away or a bending down. It comes from the root as the words incline and recline. Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of measure can be used for declination, but it is customarily measured in the degrees, minutes. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere, the Earths axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, therefore, equatorial coordinates are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be rotated to match each other. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. This similarly occurs in the Southern Hemisphere for objects with less than −90° − φ. An extreme example is the star which has a declination near to +90°. Circumpolar stars never dip below the horizon, conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earths surface. Generally, if a star whose declination is δ is circumpolar for some observer, then a star whose declination is −δ never rises above the horizon, as seen by the same observer. Likewise, if a star is circumpolar for an observer at latitude φ, neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, from the poles, declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year, the Suns declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the summer solstice, leading to the phenomenon of it being above the horizon at midnight
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Universal Time
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Universal Time is a time standard based on Earths rotation. It is a continuation of Greenwich Mean Time, i. e. the mean solar time on the Prime Meridian at Greenwich, London. In fact, the expression Universal Time is ambiguous, as there are versions of it. All of these versions of UT, except for UTC, are based on Earths rotation relative to distant celestial objects, UTC is based on International Atomic Time, with leap seconds added to keep it within 0.9 second of UT1. Prior to the introduction of time, each municipality throughout the civilized world set its official clock, if it had one. Greenwich Mean Time, where all clocks in Britain were set to the time, was established to solve this problem. Chronometers or telegraphy were used to synchronize these clocks, Standard time, as originally proposed by Scottish-Canadian Sir Sandford Fleming in 1879, divided the world into twenty-four time zones, each one covering 15 degrees of longitude. All clocks within each zone would be set to the time as the others. This location was chosen because by 1884 two-thirds of all nautical charts, the conference did not adopt Flemings time zones because they were outside the purpose for which it was called, which was to choose a basis for universal time. During the period between 1848 and 1972, all of the countries adopted time zones based on the Greenwich meridian. The term Greenwich Mean Time persists, however, in usage to this day in reference to civil timekeeping. Based on the rotation of the Earth, time can be measured by observing celestial bodies crossing the meridian every day. Astronomers found that it was accurate to establish time by observing stars as they crossed a meridian rather than by observing the position of the Sun in the sky. Nowadays, UT in relation to International Atomic Time is determined by Very Long Baseline Interferometry observations of distant quasars, the rotation of the Earth and UT are monitored by the International Earth Rotation and Reference Systems Service. The International Astronomical Union also is involved in setting standards, the rotation of the Earth is somewhat irregular, and is very gradually slowing due to tidal acceleration. Furthermore, the length of the second was determined from observations of the Moon between 1750 and 1890. All of these cause the mean solar day, on the average, to be slightly longer than the nominal 86,400 SI seconds. As UT is slightly irregular in its rate, astronomers introduced Ephemeris Time, thus, civil broadcast standards for time and frequency usually follow International Atomic Time closely, but occasionally step in order to prevent them from drifting too far from mean solar time
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Solstice
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The Solstice occurs twice each year as the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. The seasons of the year are directly connected to both the solstices and the equinoxes, the term solstice can also be used in a broader sense, as the day when this occurs. The day of the solstice has either the most sunlight of the year or the least sunlight of the year for any other than the equator. Alternative terms, with no ambiguity as to which hemisphere is the context, are June solstice and December solstice, at latitudes outside the tropics, the summer solstice marks the day when the sun appears highest in the sky. Within the tropics, the sun directly overhead from days to months before the solstice and again after the solstice. For an observer on the North Pole, the sun reaches the highest position in the sky once a year in June, the day this occurs is called the June solstice day. Similarly, for an observer on the South Pole, the sun reaches the highest position on December solstice day, when it is the summer solstice at one Pole, it is the winter solstice on the other. The suns westerly motion never ceases as the Earth is continually in rotation, however, the suns motion in declination comes to a stop at the moment of solstice. In that sense, solstice means sun-standing and this modern scientific word descends from a Latin scientific word in use in the late Roman republic of the 1st century BC, solstitium. Pliny uses it a number of times in his Natural History with a meaning that it has today. It contains two Latin-language morphemes, sol, sun, and -stitium, stoppage, the Romans used standing to refer to a component of the relative velocity of the Sun as it is observed in the sky. Relative velocity is the motion of an object from the point of view of an observer in a frame of reference, from a fixed position on the ground, the sun appears to orbit around the Earth. To an observer in a frame of reference, the planet Earth is seen to rotate about an axis. The Earths axis is tilted with respect to the plane of the Earths orbit, an observer on Earth therefore sees a solar path that is the result of both rotation and revolution. At maximum or minimum elevation, the relative motion of the Sun perpendicular to the horizon stops. Outside of the tropics, the maximum occurs at the summer solstice. The path of the Sun, or ecliptic, sweeps north and south between the northern and southern hemispheres, the days are longer around the summer solstice and shorter around the winter solstice. When the Suns path crosses the equator, the length of the nights at latitudes +L° and -L° are of equal length and this is known as an equinox
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December solstice
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The December solstice, also known as the southern solstice, is the solstice that occurs each December, typically between the 20th and the 22nd day of the month according to the Gregorian calendar. In the southern hemisphere, the December solstice is the summer solstice and it is thus the length of time between adjacent December solstices. The length of the December solstice year has been relatively stable between 6000 BC and 2000 at 49,30 to 50,00 in excess of 365 days and 5 hours, after 2000 it is getting shorter. In 4000 the excess time will be 48,52 and in 1000046,45, the following tables contain information on the length of the day on the winter solstice of the Northern Hemisphere and the summer solstice of the Southern Hemisphere. The data was collected from the website of the Finnish Meteorological Institute on 22 December 2015, the data is arranged geographically and within the tables from the shortest day to the longest one. The figures in the show the differences between the Gregorian calendar and Persian Jalāli calendar in reference to the actual yearly time of the Southern solstice. The date of the solstice is not the same as the date of the latest sunrise, because the Earth is moving along its solar orbital path, for each solar day the Earth has to do more than one full rotation. Because the Earths orbit is elliptical, the speed at which the Earth moves along its orbit varies, consequently, solar days are not the same length throughout the year. Mean time is our way of modifying this, for our convenience, making each day the same length, the maximum correction is ±15 minutes to the mean but its value changes quite rapidly around the solstices. Christmas Dies Natalis Solis Invicti Brumalia Dongzhi Festival
30.
Inanna
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Inanna was the Sumerian goddess of love, beauty, sexual desire, fertility, knowledge, wisdom, war, and combat. She was also the goddess of the E-Anna temple at the city of Uruk. She was one of the most widely venerated deities in the ancient Sumerian pantheon and her Akkadian and Babylonian equivalent was the goddess Ishtar. Several of her most important myths involve the story of her descent into and return from Kur, Inanna was the most prominent female deity in ancient Mesopotamia. As early as the Uruk period, Inanna was associated with the city of Uruk. The famous Uruk Vase depicts a row of naked men carrying various objects, bowls, vessels, and baskets of farm products and this figure was ornately dressed for a divine marriage, and attended by a servant. Especially in the Uruk period, the symbol of a ring-headed doorpost is associated with Inanna, seal impressions from the Jemdet Nasr period show a fixed sequence of city symbols including those of Ur, Larsa, Zabalam, Urum, Arina, and probably Kesh. It is likely that this list reflects the report of contributions to Inanna at Uruk from cities supporting her cult and they had been used to lock storerooms to preserve materials set aside for her cult. Inannas primary temple of worship was the Eanna, located in Uruk and her temple, the Eanna would also seem to have been taken from Anu, the head of the Sumerian pantheon, prior to the rise of Enlil of Nippur. Inannas name derives from Lady of Heaven, the cuneiform sign of Inanna, however, is not a ligature of the signs lady and sky. The view that there was a Proto-Euphratean substrate language in Southern Iraq before Sumerian is not widely accepted by modern Assyriologists, Inanna was one of the most widely venerated deities in the Sumerian pantheon. Many shrines and temples dedicated to Inanna were built along the Tigris, the deity of this fourth-millennium city was probably originally An. After its dedication to Inanna the temple seems to have housed priestesses of the goddess, a Sacred Marriage to Inanna may have conferred legitimacy on a number of rulers of Uruk. Gilgamesh is reputed to have refused marriage to Inanna, on the grounds of her misalliance with such kings as Lugalbanda, Inannas symbol is an eight-pointed star or a rosette. She was associated with lions – even then a symbol of power – and was depicted standing on the backs of two lionesses. Her cuneiform ideogram was a twisted knot of reeds, representing the doorpost of the storehouse. Inanna was associated with the planet Venus, which at time was regarded as two stars, the morning star and the evening star. There are hymns to Inanna as her astral manifestation and it also is believed that in many myths about Inanna, including Inannas Descent to the Underworld and Inanna and Shukaletuda, her movements correspond with the movements of Venus in the sky
31.
Ishtar
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Ishtar is the Mesopotamian East Semitic goddess of fertility, love, war, sex, and power. She is the counterpart to the earlier attested Sumerian Inanna, and the cognate for the later attested Northwest Semitic Aramean goddess Astarte, and the Armenian goddess Astghik. Ishtar was an important deity in Mesopotamian religion which was extant from c.3500 BCE, Ishtar symbolizes love, including that between human and animals, its power, and its danger. Ishtar was the daughter of Anu and she was particularly worshipped in the Upper Mesopotamian kingdom of Assyria, particularly at the cities of Nineveh, Ashur and Arbela, and also in the south Mesopotamian city of Uruk. Besides the lions on her gate, her symbol is an eight-pointed star, in the Babylonian pantheon, she was the divine personification of the planet Venus. Ishtar had many lovers, however, as Guirand notes, Woe to him whom Ishtar had honoured, the fickle goddess treated her passing lovers cruelly, and the unhappy wretches usually paid dearly for the favours heaped on them. Animals, enslaved by love, lost their native vigour, they fell into traps laid by men or were domesticated by them, thou has loved the lion, mighty in strength, says the hero Gilgamesh to Ishtar, and thou hast dug for him seven and seven pits. Thou hast loved the steed, proud in battle, and destined him for the halter, the goad, even for the gods Ishtars love was fatal. In her youth the goddess had loved Tammuz, god of the harvest and her cult may have involved sacred prostitution, though this is debatable. Guirand referred to her holy city Uruk as the town of the sacred courtesans, one of the most famous myths about Ishtar describes her descent to the underworld. I will bring up the dead to eat the living, and the dead will outnumber the living. The gatekeeper hurried to tell Ereshkigal, the Queen of the Underworld, Ereshkigal told the gatekeeper to let Ishtar enter, but according to the ancient decree. The gatekeeper let Ishtar into the underworld, opening one gate at a time, at each gate, Ishtar had to shed one article of clothing. When she finally passed the seventh gate, she was naked, in a rage, Ishtar threw herself at Ereshkigal, but Ereshkigal ordered her servant Namtar to imprison Ishtar and unleash sixty diseases against her. After Ishtar descended to the underworld, all activity ceased on earth. The god Papsukal reported the situation to Ea, the king of the gods, Ea created an intersex being called Asu-shu-namir and sent them to Ereshkigal, telling them to invoke the name of the great gods against her and to ask for the bag containing the waters of life. Ereshkigal was enraged when she heard Asu-shu-namirs demand, but she had to them the water of life. Asu-shu-namir sprinkled Ishtar with this water, reviving her, then, Ishtar passed back through the seven gates, getting one article of clothing back at each gate, and was fully clothed as she exited the last gate
32.
Ishtar Gate
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The Ishtar Gate was the eighth gate to the inner city of Babylon. It was constructed in about 575 BCE by order of King Nebuchadnezzar II on the side of the city. It was excavated in the early 20th century and a reconstruction using original bricks is now shown in the Pergamon Museum, Berlin. Dedicated to the Babylonian goddess Ishtar, the gate was constructed using glazed brick with alternating rows of bas-relief mušḫuššu and aurochs, symbolizing the gods Marduk, the roof and doors of the gate were of cedar, according to the dedication plaque. The gate was covered in lapis lazuli, a deep-blue semi-precious stone that was revered in antiquity due to its vibrancy and these blue glazed bricks would have given the façade a jewel-like shine. Through the gate ran the Processional Way, which was lined with walls showing about 120 lions, bulls, dragons and flowers on enameled yellow and black glazed bricks, the gate itself depicted only gods and goddesses. These included Ishtar, Adad and Marduk, during celebrations of the New Year, statues of the deities were paraded through the gate and down the Processional Way. The gate, being part of the Walls of Babylon, was considered one of the original Seven Wonders of the World and it was replaced on that list by the Lighthouse of Alexandria from the third century BC. A reconstruction of the Ishtar Gate and Processional Way was built at the Pergamon Museum in Berlin out of material excavated by Robert Koldewey and it stands 14 m high and 30 m wide. The excavation ran from 1902 to 1914, and, during time,14 m of the foundation of the gate was uncovered. Claudius James Rich, British resident of Baghdad and a self-taught historian, acting as a scholar and collecting field data, he was determined to discover the wonders to the ancient world. C. J. Richs topographical records of the ruins in Babylon were the first ever published and it was reprinted in England no fewer than three times. C. J. Robert Koldewey, a successful German excavator, had previous work for the Royal Museum of Berlin, with his excavations at Surghul. Koldeweys part in Babylons excavation began in 1899, the method that the British were comfortable with was excavating tunnels and deep trenches, which was damaging the mud brick architecture of the foundation. Instead, it was suggested that the team focus on tablets. Despite the destructive nature of the used, the recording of data was immensely more thorough than in previous Mesopotamian excavations. Walter Andre, one of Koldeweys many assistants, was an architect and a draftsman and his contribution was documentation and reconstruction of Babylon. A small museum was built at the site and Andre was the museums first director, one of most complex and impressive architectural reconstructions in the history of archaeology, was the rebuilding of Babylons Ishtar gate and processional way in Berlin
33.
Eanna
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É is the Sumerian word or symbol for house or temple. The Sumerian term É. GAL denoted a citys main building, in the texts of Lagash, the É. GAL is the center of the ensis administration of the city, and the site of the city archives. Sumerian É. GAL palace is the etymology of Semitic words for palace, temple, such as Hebrew היכל heikhal. It has thus been speculated that the word É originated from something akin to *hai or *ˀai, in the house, Enki drove in the foundation pegs, while Nanshe, the daughter of Eridu, took care of the oracular messages. The mother of Lagash, holy Gatumdug, gave birth to its bricks amid cries, and Bau, en and lagar priests were detailed to the house to provide maintenance for it. The Anuna gods stood there full of admiration, e-ab-lua temple to Suen in Urum E-ab-shaga-la temple to Ninmarki in Gu-aba E-abzu, temple of the abzu temple to Enki in Eridu. The Temples of Babylonia and Assyria, the American Journal of Semitic Languages and Literatures
34.
Tammuz (deity)
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The Levantine Adonis, who was drawn into the Greek pantheon, was considered by Joseph Campbell among others to be another counterpart of Tammuz, son and consort. The Aramaic name Tammuz seems to have derived from the Akkadian form Tammuzi. The later standard Sumerian form, Dumu-zid, in turn became Dumuzi in Akkadian, tamuzi also is Dumuzid or Dumuzi. In cult practice, the dead Tammuz was widely mourned in the Ancient Near East, locations associated in antiquity with the site of his death include both Harran and Byblos, among others. O Dumuzid of the mouth, of the ever kind eyes, she sobs tearfully, O you of the fair-spoken mouth, of the ever kind eyes. Lad, husband, lord, sweet as the date, O Dumuzid, then said he unto to me, Hast thou seen this, O son of man. Turn thee yet again, and thou shalt see greater abominations than these, —Ezekiel 8, 14-15 Tammuz idol worship was inconsistent with Yahwism. Ezekiels testimony is the only mention of Tammuz in the Hebrew Bible, though echoes of Tammuz have been seen in the Book of Isaiah. Other Sumerian texts showed that kings were to be married to Inanna in a sacred marriage, a number of pastoral poems and songs relate the love affair of Inanna and Dumuzid the shepherd. A text recovered in 1963 recounts The Courtship of Inanna and Dumuzi in terms that are tender, ereshkigal is in mourning at the death of her consort, Gugalanna. She passed through seven gates and at each one was required to leave a garment or an ornament so that when she had passed through the gate she was a simple woman. Despite warnings about her presumption, she did not turn back, immediately the Anunnaki of the underworld judged her, gazed at her with the eyes of death, and she became a corpse, hung up on a meathook. This is the form of the myth as it appeared in M. Jastrows Descent of the Goddess Ishtar into the Lower World,1915. New texts uncovered in 1963 filled in the story in another fashion, showing that Dumuzi was in fact consigned to the Underworld himself. Inannas faithful servant attempted to get help from the other gods, the details of Enki/Eas plan differ slightly in the two surviving accounts, but in the end, Inanna/Ishtar was resurrected. However, a conservation of souls law required her to find a replacement for herself in Kur. She went from one god to another, but each one pleaded with her and she had not the heart to go through with it until she found Dumuzid/Tammuz richly dressed, Inanna/Ishtar immediately set her accompanying demons on Dumuzid/Tammuz. At this point the Akkadian text fails as Tammuz sister Belili, introduced for the first time, strips herself of her jewelry in mourning but claims that Tammuz and the dead will come back
35.
Dummuzi
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The Levantine Adonis, who was drawn into the Greek pantheon, was considered by Joseph Campbell among others to be another counterpart of Tammuz, son and consort. The Aramaic name Tammuz seems to have derived from the Akkadian form Tammuzi. The later standard Sumerian form, Dumu-zid, in turn became Dumuzi in Akkadian, tamuzi also is Dumuzid or Dumuzi. In cult practice, the dead Tammuz was widely mourned in the Ancient Near East, locations associated in antiquity with the site of his death include both Harran and Byblos, among others. O Dumuzid of the mouth, of the ever kind eyes, she sobs tearfully, O you of the fair-spoken mouth, of the ever kind eyes. Lad, husband, lord, sweet as the date, O Dumuzid, then said he unto to me, Hast thou seen this, O son of man. Turn thee yet again, and thou shalt see greater abominations than these, —Ezekiel 8, 14-15 Tammuz idol worship was inconsistent with Yahwism. Ezekiels testimony is the only mention of Tammuz in the Hebrew Bible, though echoes of Tammuz have been seen in the Book of Isaiah. Other Sumerian texts showed that kings were to be married to Inanna in a sacred marriage, a number of pastoral poems and songs relate the love affair of Inanna and Dumuzid the shepherd. A text recovered in 1963 recounts The Courtship of Inanna and Dumuzi in terms that are tender, ereshkigal is in mourning at the death of her consort, Gugalanna. She passed through seven gates and at each one was required to leave a garment or an ornament so that when she had passed through the gate she was a simple woman. Despite warnings about her presumption, she did not turn back, immediately the Anunnaki of the underworld judged her, gazed at her with the eyes of death, and she became a corpse, hung up on a meathook. This is the form of the myth as it appeared in M. Jastrows Descent of the Goddess Ishtar into the Lower World,1915. New texts uncovered in 1963 filled in the story in another fashion, showing that Dumuzi was in fact consigned to the Underworld himself. Inannas faithful servant attempted to get help from the other gods, the details of Enki/Eas plan differ slightly in the two surviving accounts, but in the end, Inanna/Ishtar was resurrected. However, a conservation of souls law required her to find a replacement for herself in Kur. She went from one god to another, but each one pleaded with her and she had not the heart to go through with it until she found Dumuzid/Tammuz richly dressed, Inanna/Ishtar immediately set her accompanying demons on Dumuzid/Tammuz. At this point the Akkadian text fails as Tammuz sister Belili, introduced for the first time, strips herself of her jewelry in mourning but claims that Tammuz and the dead will come back
36.
Tehran
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Tehran is the capital of Iran and Tehran Province. It is ranked 29th in the world by the population of its metropolitan area, in the Classical era, part of the present-day city of Tehran was occupied by a Median city that in the Avesta occurs as Rhaga. It was destroyed by the Mongols in the early 13th century, the capital has been moved several times throughout the history, and Tehran is the 32nd national capital of Iran. The city was the seat of the Qajars and Pahlavis, the two last imperial dynasties of Iran. It is home to historical collections, such as the royal complexes of Golestan, Sadabad. Large scale demolition and rebuilding began in the 1920s, and Tehran has been a destination for the migrations from all over Iran since the 20th century. Tabiat Bridge, which was completed in 2014, is considered the third symbol of the city. There have been plans to relocate Irans capital from Tehran to another area, due mainly to air pollution, to date, no definitive plans have been approved. A2016 survey of 230 cities by consultant Mercer ranked Tehran 203rd for quality of living, according to the Global Destinations Cities Index in 2016, Tehran is among the top ten fastest growing destinations. The origin of the name Tehran is uncertain, the settlement of Tehran dates back over 7,000 years. The present-day city of Tehran was a suburb of an important Median city that was known as Rhaga in Old Persian, in the Avestas Videvdat, Rhaga is mentioned as the twelfth sacred place created by the Ohrmazd. In Old Persian inscriptions, Rhaga appears as a province and it was a major area for the Iranian tribes of Medes and Achaemenids. From Rhaga, Darius the Great sent reinforcements to his father Hystaspes, in some Middle Persian texts, Rhaga is given as the birthplace of Zoroaster, although modern historians generally place the birth of Zoroaster in Khorasan. Derived into Modern Persian as Rey, it now as a city located towards the southern end of the modern-day city of Tehran. Mount Damavand, the highest peak of Iran, which is located near Tehran, is an important location in Ferdowsis Shahname, the long Iranian epic poem that is based on the ancient epics of Iran. It appears in the epics as the birthplace of Manuchehr, the residence of Keyumars, the place where Freydun binds the dragon fiend Aži Dahāka, during the Sassanid era, in 641, Yazdgerd III issued his last appeal to the nation from Rey, before fleeing to Khorasan. Rey was dominated by the Parthian Mihran family, and Siyavakhsh—the son of Mihran the son of Bahram Chobin—who resisted the Muslim Invasion, because of this resistance, when the Arabs captured Rey, they ordered the town to be destroyed and ordered Farrukhzad to rebuild the town anew. In the 9th century, Tehran was a well known village, but less known than the city of Rey, the medieval writer Najm od Din Razi declared the population of Rey about 500,000 before the Mongol Invasion
37.
Indian national calendar
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The Indian national calendar, sometimes called the Saka calendar, is the official civil calendar in use in India along with the Vikram Samvat calendar. It is used, alongside the Gregorian calendar, by The Gazette of India, in broadcasts by All India Radio and in calendars. The Saka calendar is used in Java and Bali among Indonesian Hindus. Nyepi, the Day of Silence, is a celebration of the Saka new year in Bali, nepals Nepal Sambat evolved from the Saka calendar. The term may also refer to the Hindu calendar, the Saka era is also commonly used by other calendars. The calendar months follow the signs of the tropical zodiac rather than the sidereal zodiac normally used with Hindu calendar, in leap years, Chaitra has 31 days and starts on March 21 instead. The months in the first half of the year all have 31 days, the names of the months are derived from older, Hindu lunisolar calendars, so variations in spelling exist, and there is a possible source of confusion as to what calendar a date belongs to. Years are counted in the Saka Era, which starts its year 0 in the year 78 of the Common Era. To determine leap years, add 78 to the Saka year - if the result is a year in the Gregorian calendar. Its structure is like the Persian calendar, despite this effort, local variations based on older sources such as the Surya Siddhanta may still exist. Senior Indian Astrophysicist Meghnad Saha was the head of the Calendar Reform Committee under the aegis of the Council of Scientific, other members of the Committee were, A. C. Banerjee, K. K. Daftari, J. S. Karandikar, Gorakh Prasad, R. V. Vaidya and it was Saha’s effort, which led to the formation of the Committee. The task before the Committee was to prepare an accurate calendar based on scientific study, the Committee had to undertake a detailed study of different calendars prevalent in different parts of the country. The task was complicated by the fact that religion and local sentiments were integral to those calendars. Indias first prime minister, Jawaharlal Nehru, in his preface to the Report of the Committee, published in 1955, wrote, “They represent past political divisions in the country…. ”Usage started officially at Chaitra 1,1879, Saka Era, or March 22,1957, Dionysian Era. However, government officials seem to ignore the New Years Day of this calendar in favour of the religious calendar. Mapping Time, The Calendar and its History by E. G, Calendars and their History Indian Calendars Positional astronomy in India Indian National Calendar abstract
38.
Julian calendar
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The Julian calendar, proposed by Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on 1 January 45 BC, by edict, the Julian calendar gains against the mean tropical year at the rate of one day in 128 years. For the Gregorian the figure is one day in 3,030 years, the difference in the average length of the year between Julian and Gregorian is 0. 002%. The Julian calendar has a year of 365 days divided into 12 months. A leap day is added to February every four years, the Julian year is, therefore, on average 365.25 days long. It was intended to approximate the tropical year, as a result, the calendar year gains about three days every four centuries compared to observed equinox times and the seasons. This discrepancy was corrected by the Gregorian reform of 1582, consequently, the Julian calendar is currently 13 days behind the Gregorian calendar. Egypt converted on 20 December 1874/1 January 1875, turkey switched on 16 February/1 March 1917. Russia changed on 1/14 February 1918, Greece made the change for civil purposes on 16 February/1 March 1923 - the national day, which was a religious holiday, was to remain on the old calendar. Most Christian denominations in the west and areas evangelised by western churches have replaced the Julian calendar with the Gregorian as the basis for their liturgical calendars. However, most branches of the Eastern Orthodox Church still use the Julian calendar for calculating the date of Easter, some Orthodox churches have adopted the Revised Julian calendar for the observance of fixed feasts, while other Orthodox churches retain the Julian calendar for all purposes. The Julian calendar is used by the Berbers of the Maghreb in the form of the Berber calendar. In the form of the Alexandrian calendar, it is the basis for the Ethiopian calendar, during the changeover between calendars and for some time afterwards, dual dating was used in documents and gave the date according to both systems. In contemporary as well as texts that describe events during the period of change. The ordinary year in the previous Roman calendar consisted of 12 months, in addition, a 27- or 28-day intercalary month, the Mensis Intercalaris, was sometimes inserted between February and March. The net effect was to add 22 or 23 days to the year, some say the mensis intercalaris always had 27 days and began on either the first or the second day after the Terminalia. According to the later writers Censorinus and Macrobius, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, alternately 377 and 378 days long. In this system, the average Roman year would have had 366 1⁄4 days over four years, Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377 days
39.
Relief
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Relief is a sculptural technique where the sculpted elements remain attached to a solid background of the same material. The term relief is from the Latin verb relevo, to raise, to create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane. What is actually performed when a relief is cut in from a surface of stone or wood is a lowering of the field. The technique involves considerable chiselling away of the background, which is a time-consuming exercise. In other materials such as metal, clay, plaster stucco, ceramics or papier-mâché the form can be just added to or raised up from the background, and monumental bronze reliefs are made by casting. There are different degrees of relief depending on the degree of projection of the form from the field. There is also sunk relief, which was restricted to Ancient Egypt. However the distinction between high relief and low relief is the clearest and most important, and these two are generally the only used to discuss most work. Hyphens may or may not be used in all these terms, works in the technique are described as in relief, and, especially in monumental sculpture, the work itself is a relief. Reliefs are common throughout the world on the walls of buildings and a variety of settings. Relief is more suitable for depicting complicated subjects with figures and very active poses, such as battles. Most ancient architectural reliefs were painted, which helped to define forms in low relief. Rock reliefs are carved into solid rock in the open air. This type is found in cultures, in particular those of the Ancient Near East and Buddhist countries. A stele is a standing stone, many of these carry reliefs. The distinction between high and low relief is somewhat subjective, and the two are often combined in a single work. In particular, most later high reliefs contain sections in low relief, a low relief or bas-relief is a projecting image with a shallow overall depth, for example used on coins, on which all images are in low relief. Other versions distort depth much less and it is a technique which requires less work, and is therefore cheaper to produce, as less of the background needs to be removed in a carving, or less modelling is required
40.
Persepolis
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Persepolis or Parsa, also known as Takht-e-Jamshid, was the ceremonial capital of the Achaemenid Empire. Persepolis is situated 60 km northeast of the city of Shiraz in Fars Province, the earliest remains of Persepolis date back to 515 BC. It exemplifies the Achaemenid style of architecture, UNESCO declared the ruins of Persepolis a World Heritage Site in 1979. The English word Persepolis is derived from Ancient Greek Persépolis, a compound of Pérsēs and pólis, to the ancient Persians, the city was known as Pārsa. Persepolis is near the small river Pulvar, which flows into the Kur River, the site includes a 125,000 square meter terrace, partly artificially constructed and partly cut out of a mountain, with its east side leaning on Rahmet Mountain. The other three sides are formed by retaining walls, which vary in height with the slope of the ground, rising from 5–13 metres on the west side was a double stair. From there, it slopes to the top. To create the level terrace, depressions were filled with soil and heavy rocks, archaeological evidence shows that the earliest remains of Persepolis date back to 515 BC. As the residence of the rulers of the empire, however, the countrys true capitals were Susa, Babylon and Ecbatana. This accounts for the fact that the Greeks were not acquainted with the city until Alexander the Great took, Darius I ordered the construction of the Apadana and the Council Hall, as well as the main imperial Treasury and its surroundings. These were completed during the reign of his son, Xerxes I, further construction of the buildings on the terrace continued until the downfall of the Achaemenid Empire. Around 519 BC, construction of a stairway was begun. The stairway was initially planned to be the entrance to the terrace 20 metres above the ground. The dual stairway, known as the Persepolitan Stairway, was built symmetrically on the side of the Great Wall. The 111 steps measured 6.9 metres wide, with treads of 31 centimetres and rises of 10 centimetres, originally, the steps were believed to have been constructed to allow for nobles and royalty to ascend by horseback. New theories, however, suggest that the shallow risers allowed visiting dignitaries to maintain an appearance while ascending. The top of the led to a small yard in the north-eastern side of the terrace. Grey limestone was the building material used at Persepolis
41.
Culture of Iran
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The culture of Iran or culture of Persia is one of the oldest in the world. Thus an eclectic cultural elasticity has been said to be one of the key defining characteristics of the Persian spirit, furthermore, Irans culture has manifested itself in several facets throughout the history of Iran as well as the Caucasus, Central Asia, Anatolia, and Mesopotamia. They are not the same and the cultures of the peoples of Greater Persia are the focus of this article, Iran has one of the richest art heritages in world history and encompasses many disciplines including architecture, painting, weaving, pottery, calligraphy, metalworking and stonemasonry. There is also a very vibrant Iranian modern and contemporary art scene, Iranian art has gone through numerous phases. The unique aesthetics of Iran is evident from the Achaemenid reliefs in Persepolis to the paintings of Bishapur. The Islamic era brought drastic changes to the styles and practice of the arts, the Qajarid era was the last stage of classical Persian art, before modernism was imported and suffused into elements of traditionalist schools of aesthetics. Several languages are spoken in different regions of Iran, the predominant language and national language is Persian, which is spoken across the country. Smaller languages spread in other regions notably include Talysh, Georgian, Armenian, Assyrian, Persian literature inspired Goethe, Ralph Waldo Emerson, and many others, and it has been often dubbed as a most worthy language to serve as a conduit for poetry. Dialects of Persian are sporadically spoken throughout the region from China to Syria to Russia, Zoroastrianism was the national faith of Iran for more than a millennium before the Arab conquest. It has had an influence on Iranian philosophy, culture. Followers of the Bahai faith comprise the largest non-Muslim minority in Iran, followers of the Bahai faith are scattered throughout small communities in Iran, although there seems to be a large population of people who follow the Bahai faith in Tehran. Most of the Bahai are of Persian descent, although there seem to be many among the Azerbaijani, thus, Christians that live in Iran are primarily descendants of indigenous Christians that were converted during the 19th and 20th centuries. In addition to Christianity and Judaism, Zoroastrianism is another officially recognized religion in Iran, in addition, although there have been isolated incidences of prejudice against Zoroastrians, most followers of this faith have not been persecuted for being followers of this faith. The Persian year begins in the vernal equinox, if the astronomical vernal equinox comes before noon, if the equinox falls after noon, then the next day is the official first day of the Persian year. The Persian Calendar, which is the calendar of Iran, is a solar calendar with a starting point that is the same as the Islamic calendar. According to the Iran Labor Code, Friday is the day of rest. Government official working hours are from Saturday to Wednesday, additional holidays include The Anniversary of the Uprising Against the Shah, Ashoura, Victory of the 1979 Islamic Revolution, Sizdah-Bedar—Public Outing Day to end Nowrooz, and Islamic Republic Day. There are two stages in a wedding ritual in Iran
42.
Nowruz
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It has been celebrated for over 3,000 years in Western Asia, Central Asia, the Caucasus, the Black Sea Basin and the Balkans. It marks the first day of the first month in the Iranian calendar, Nowruz is the day of the vernal equinox, and marks the beginning of spring in the Northern Hemisphere. It usually occurs on 21 March or the previous or following day, the moment the sun crosses the celestial equator and equalizes night and day is calculated exactly every year, and families gather together to observe the rituals. Although having Iranian and religious Zoroastrian origins, Nowruz has been celebrated by people from diverse ethno-linguistic communities for thousands of years and it is a secular holiday for most celebrants that is enjoyed by people of several different faiths, but remains a holy day for Zoroastrians. The term Nowruz is a Persian compound word, consisting of the words now, now, which means new and descends from Proto-Indo-European *néṷos, is cognate with English new, German neu, Latin novus, Russian novyj and Sanskrit náva. Ruz, which day in Modern Persian, is descended from Proto-Iranian *raučah-. The original meaning of the word, however, was light and it is related to Armenian loys, English light, Latin lux, Sanskrit rúci and Slovenian luč. The Persian pronunciation differs in the dialects of the language. While the eastern dialects have preserved the diphthong nau, the western dialects usually pronounce it with the diphthong now, a variety of spelling variations for the word Nowruz exist in English-language usage. Random House provides the spelling Nowruz, merriam-Webster recognizes only the spelling Nauruz. Nowruz is partly rooted in the tradition of Iranian religions, such as Mitraism and Zoroastrianism, in Mitraism, festivals had a deep linkage with the suns light. The Iranian festivals such as Mehrgan, Tirgan, and the eve of Chelle ye Zemestan also had an origin in the Sun god, Zoroastrian practices were dominant for much of the history of ancient Iran. In Zoroastrianism, the seven most important Zoroastrian festivals are the six Gahambar festivals and Nowruz, between sunset on the day of the sixth Gahambar and sunrise of Nowruz, Hamaspathmaedaya was celebrated. This and the Gahambars are the only named in the surviving text of the Avesta. The 10th-century scholar Biruni, in his work Kitab al-Tafhim li Awail Sinaat al-Tanjim, besides the Iranian calendar, various festivals of Greeks, Jews, Arabs, Sabians, and other nations are mentioned in the book. In the section on the Iranian calendar, he mentions Nowruz, Sadeh, Tirgan, Mehrgan, according to him, It is the belief of the Iranians that Nowruz marks the first day when the universe started its motion. It has been suggested that the famous Persepolis complex, or at least the palace of Apadana and it was an important day during the time of the Achaemenids, where kings from different nations under the Achaemenid Empire used to bring gifts to the King of Kings of Iran. It was, therefore, an auspicious occasion for the ancient Iranian peoples
