1.
North
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North is one of the four cardinal directions or compass points. It is the opposite of south and is perpendicular to east and west, North is a noun, adjective, or adverb indicating direction or geography. The word north is related to the Old High German nord, the Latin word borealis comes from the Greek boreas north wind, north, which, according to Ovid, was personified as the son of the river-god Strymon, the father of Calais and Zetes. Septentrionalis is from septentriones, the seven plow oxen, a name of Ursa Maior, the Greek ἀρκτικός is named for the same constellation, and is the source of the English word Arctic. For example, in Lezgian, kefer can mean both disbelief and north, since to the north of the Muslim Lezgian homeland there are areas formerly inhabited by non-Muslim Caucasian, in many languages of Mesoamerica, north also means up. The direction north is associated with colder climates because most of the worlds land at high latitudes is located in the Northern Hemisphere. By convention, the top side of a map is often north, to go north using a compass for navigation, set a bearing or azimuth of 0° or 360°. North is specifically the direction that, in Western culture, is treated as the fundamental direction, on any rotating non-astronomical object, north denotes the side appearing to rotate counter-clockwise when viewed from afar along the axis of rotation. Magnetic north is of interest because it is the direction indicated as north on a properly functioning magnetic compass, the difference between it and true north is called the magnetic declination. But simple generalizations on the subject should be treated as unsound, maps intended for usage in orienteering by compass will clearly indicate the local declination for easy correction to true north. Maps may also indicate grid north, which is a term referring to the direction northwards along the grid lines of a map projection. The visible rotation of the sky around the visible celestial pole provides a vivid metaphor of that direction corresponding to up. Thus the choice of the north as corresponding to up in the hemisphere, or of south in that role in the southern, is, prior to worldwide communication, anything. On the contrary, it is of interest that Chinese and Islamic culture even considered south as the top end for maps. Up is a metaphor for north, the notion that north should always be up and east at the right was established by the Greek astronomer Ptolemy. While the choice of north over south as prime direction reflects quite arbitrary historical factors and their folk definitions are, respectively, where the sun rises and where it sets. The true folk-astronomical definitions of east and west are the directions, an angle from the prime direction. Being the default direction on the compass, north is referred to frequently in Western popular culture, some examples include, The phrase north of X is often used by Americans to mean more than X or greater than X, i. e
2.
Crown (headgear)
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In art, the crown may be shown being offered to those on Earth by angels. In religious art, a crown of stars is used similarly to a halo, crowns worn by rulers often contain jewels. A crown is often an emblem of the monarchy, a monarchs government, the word itself is used, particularly in Commonwealth countries, as an abstract name for the monarchy itself, as distinct from the individual who inhabits it. A specific type of crown is employed in heraldry under strict rules, costume headgear imitating a monarchs crown is also called a crown. Such costume crowns may be worn by actors portraying a monarch, people at parties, or ritual monarchs such as the king of a Carnival krewe. The nuptial crown, sometimes called a coronal, worn by a bride, in the present day, it is most common in Eastern Orthodox cultures. The Eastern Orthodox marriage service has a section called the crowning, wherein the bride and groom are crowned as king, in Greek weddings, the crowns are diadems usually made of white flowers, synthetic or real, often adorned with silver or mother of pearl. They are placed on the heads of the newlyweds and are held together by a ribbon of white silk and they are then kept by the couple as a reminder of their special day. In Slavic weddings, the crowns are made of ornate metal, designed to resemble an imperial crown. A parish usually owns one set to use for all the couples that are married there since these are more expensive than Greek-style crowns. This was common in Catholic countries in the past, a Crown of thorns according to the Bible, was placed on the head of Jesus before his crucifixion and has become a common symbol of martyrdom. According to Roman Catholic tradition, the Blessed Virgin Mary was crowned as Queen of Heaven after her assumption into heaven and she is often depicted wearing a crown, and statues of her in churches and shrines are ceremonially crowned during May. The Crown of Immortality is also common in historical symbolism, dancers of certain traditional Thai dances often wear crowns on their head. These are inspired in the worn by deities and by kings. Three distinct categories of crowns exist in those monarchies that use crowns or state regalia, coronation, worn by monarchs when being crowned. State, worn by monarchs on other state occasions, consort crowns, worn by queens consort, signifying rank granted as a constitutional courtesy protocol. In Classical antiquity, the crown that was awarded to people other than rulers, such as triumphal military generals or athletes, was actually a wreath or chaplet. Numerous crowns of various forms were used in antiquity, such as the Hedjet, Deshret, the Pschent double crown and it was referred to as the chaplet studded with sunbeams” by Lucian, about 180 AD
3.
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
4.
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
5.
88 modern constellations by area
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The table below ranks the 88 modern constellations by the solid angle that they subtend in the sky, measured in square degrees and millisteradians. Before Delportes work, there was no standard list of the boundaries of each constellation and this skew will increase over the years and centuries to come. However, this does not change the angle of any constellation
6.
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
7.
Bayer designation
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A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellations Latin name. The original list of Bayer designations contained 1,564 stars, most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria. Bayer assigned a lower-case Greek letter, such as alpha, beta, gamma, for example, Aldebaran is designated α Tauri, which means Alpha of the constellation Taurus. A single constellation may contain fifty or more stars, but the Greek alphabet has only twenty-four letters, when these ran out, Bayer began using Latin letters, upper case A, followed by lower case b through z, for a total of another 24 letters. Bayer never went beyond z, but later added more designations using both upper and lower case Latin letters, the upper case letters following the lower case ones in general. Examples include s Carinae, d Centauri, G Scorpii, and N Velorum, the last upper-case letter used in this way was Q. Bayer catalogued only a few stars too far south to be seen from Germany, in most constellations, Bayer assigned Greek and Latin letters to stars within a constellation in rough order of apparent brightness, from brightest to dimmest. Since the brightest star in a majority of constellations is designated Alpha, in Bayers day, however, stellar brightness could not be measured precisely. Within each magnitude class, Bayer made no attempt to arrange stars by relative brightness, as a result, the brightest star in each class did not always get listed first in Bayers order. Occasionally the order looks quite arbitrary, of the 88 modern constellations, there are at least 30 in which Alpha is not the brightest star, and four of those lack an alpha star altogether. Orion provides an example of Bayers method. Bayer first designated Betelgeuse and Rigel, the two 1st-magnitude stars, as Alpha and Beta from north to south, with Betelgeuse coming ahead of Rigel, Bayer then repeated the procedure for the stars of the 2nd magnitude, labeling them from gamma through zeta in top-down order. The First to Rise in the East order is used in a number of instances, Castor and Pollux of Gemini may be an example of this, Pollux is brighter than Castor, but the latter rises earlier and was assigned alpha. In this case, Bayer may also have influenced by the traditional order of the mythological names Castor and Pollux. Although the brightest star in Draco is Eltanin, Thuban was assigned alpha by Bayer because, due to precession, sometimes there is no apparent order, as exemplified by the stars in Sagittarius, where Bayers designations appear almost random to the modern eye. Alpha and Beta Sagittarii are perhaps the most anomalously designated stars in the sky, the order of the letters assigned in Sagittarius does correspond to the magnitudes as illustrated on Bayers chart, but the latter do not agree with modern determinations of the magnitudes. Bayer designations added by later astronomers generally were ordered by magnitude, in Libra, for example, the new designations sigma, tau, and upsilon were chosen to avoid conflict with Bayers earlier designations, even though several stars with earlier letters are not as bright. In Cygnus, for example, Bayers fixed stars run through g, Bayer did not intend such labels as catalog designations, but some have survived to refer to astronomical objects, P Cygni for example is still used as a designation for Nova Cyg 1600
8.
Exoplanet
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An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first scientific detection of an exoplanet was in 1988, HARPS has discovered about a hundred exoplanets while the Kepler space telescope has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives, on average, there is at least one planet per star, with a percentage having multiple planets. About 1 in 5 Sun-like stars have an Earth-sized planet in the habitable zone, the least massive planet known is Draugr, which is about twice the mass of the Moon. There are planets that are so near to their star that they take only a few hours to orbit, some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way, the nearest exoplanet is Proxima Centauri b, located 4.2 light-years from Earth and orbiting Proxima Centauri, the closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life, there is special interest in planets that orbit in a stars habitable zone, where it is possible for liquid water, a prerequisite for life on Earth, to exist on the surface. The study of planetary habitability also considers a range of other factors in determining the suitability of a planet for hosting life. The rogue planets in the Milky Way possibly number in the billions, the convention for designating exoplanets is an extension of the system used for designating multiple-star systems as adopted by the International Astronomical Union. For exoplanets orbiting a star, the designation is normally formed by taking the name or, more commonly, designation of its parent star. The first planet discovered in a system is given the designation b, if several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbital size. A provisional IAU-sanctioned standard exists to accommodate the designation of circumbinary planets, a limited number of exoplanets have IAU-sanctioned proper names. Various detection claims made in the century were rejected by astronomers. The first scientific detection of an exoplanet began in 1988, However, the first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a star was made in 1995. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method, in the eighteenth century the same possibility was mentioned by Isaac Newton in the General Scholium that concludes his Principia. Claims of exoplanet detections have been made since the nineteenth century, some of the earliest involve the binary star 70 Ophiuchi. In 1855 William Stephen Jacob at the East India Companys Madras Observatory reported that orbital anomalies made it highly probable that there was a body in this system
9.
Alpha Coronae Borealis
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Alpha Coronae Borealis, also named Alphecca, is a binary star in the constellation of Corona Borealis. It is located about 75 light years from the Sun, the primary component is a white main sequence star that has a stellar classification of A0V and 2.6 times the mass of the Sun. Estimates of the stars radius range from 2.89 to 3.04 times the radius of the Sun, an excess of infrared radiation at 24 μm and 70 μm has been detected about the primary star by the IRAS. This suggests the presence of a disc of dust and material around Alphecca. The disk extends out to a radius of around 60 astronomical units, the secondary component is a yellow main sequence star with an estimated stellar class of G5,0.92 times the Suns mass and 0.90 times the Suns radius. The X-ray luminosity of this star is 6 ×1028 erg s−1 and this higher activity level is expected for a young star of this class. The corona has a temperature of about 5 MK, which is hotter than the Suns corona. The upper limit of 14 km/s for the rotation velocity is equivalent to a rotation period of 3 days. More likely, the period is 7–9 days. The stars are orbiting each other in an eccentric orbit one every 17.36 days. Because the plane of orbit is inclined at an angle of 88. 2° to the line of sight to the Earth. The periodic eclipses result in a variation of +2.21 to +2.32. The space velocity components of this system are U = +14.257, V = +0.915. α CrB is believed to be a member of the Ursa Major Moving Group of stars that have a motion through space. α Coronae Borealis is the stars Bayer designation and it bore the traditional names Alphecca, Gemma, Gnosia, and Asteroth. Alphecca is Arabic, short for نير الفكّة nayyir al-fakka the bright of the broken, Gnosia is also Latin, short for Gnōsia stella corōnæ star of the crown of Knossos. Asteroth is Hebrew, עשתרות ‘ašterôt Astarte, as the brightest star in Corona Borealis, it lent its name to Alphekka Meridiana, the brightest in the constellation of Corona Australis. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalog, the WGSNs first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Alphecca for this star
10.
Apparent magnitude
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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m
11.
Messier object
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The Messier objects are a set of over 100 astronomical objects first listed by French astronomer Charles Messier in 1771. The number of objects in the lists he published reached 103, a similar list had been published in 1654 by Giovanni Hodierna, but attracted attention only recently and was probably not known to Messier. The first edition covered 45 objects numbered M1 to M45, the first such addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding a note Messier made in a copy of the 1781 edition of the catalogue. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, M102 was observed by Méchain, who communicated his notes to Messier. Méchain later concluded that this object was simply a re-observation of M101, though sources suggest that the object Méchain observed was the galaxy NGC5866. Messiers final catalogue was included in the Connaissance des Temps for 1784 and these objects are still known by their Messier number from this list. Messier lived and did his work at the Hôtel de Cluny. The list he compiled contains only objects found in the sky area he could observe and he did not observe or list objects visible only from farther south, such as the Large and Small Magellanic Clouds. A summary of the astrophysics of each Messier object can be found in the Concise Catalog of Deep-sky Objects, in early spring, astronomers sometimes gather for Messier marathons, when all of the objects can be viewed over a single night
12.
Meteor shower
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A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of debris called meteoroids entering Earths atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate, intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1000 meteors an hour. The Meteor Data Centre lists about 600 suspected meteor showers of which about 100 are well established, the first great storm in modern times was the Leonids of November 1833. American Denison Olmsted explained the event most accurately, after spending the last weeks of 1833 collecting information he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. Work continued, however, coming to understand the nature of showers though the occurrences of storms perplexed researchers. In the 1890s, Irish astronomer George Johnstone Stoney and British astronomer Arthur Matthew Weld Downing, were the first to attempt to calculate the position of the dust at Earths orbit. They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899, Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earths orbit. The same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut in Berlin, although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of showers for the Leonids. A graph from it was adapted and re-published in Sky and Telescope and it showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. In 1985, E. D. Kondrateva and E. A. Reznikov of Kazan State University first correctly identified the years when dust was released which was responsible for several past Leonid meteor storms, in 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails. In anticipation of the 1999 Leonid storm, Robert H. McNaught, David Asher, in 2006 Jenniskens has published predictions for future dust trail encounters covering the next 50 years. Jérémie Vaubaillon continues to update predictions based on each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides. Because meteor shower particles are all traveling in parallel paths, and at the same velocity and this radiant point is caused by the effect of perspective, similar to parallel railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. Meteor showers are almost always named after the constellation from which the appear to originate. This fixed point slowly moves across the sky during the due to the Earth turning on its axis. The radiant also moves slightly from night to night against the stars due to the Earth moving in its orbit around the sun
13.
Hercules (constellation)
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Hercules is a constellation named after Hercules, the Greek mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and it is the fifth largest of the modern constellations. Hercules is bordered by Draco to the north, Boötes, Corona Borealis, and Serpens Caput to the east, Ophiuchus to the south, Aquila to the southwest, and Sagitta, Vulpecula, and Lyra to the west. Covering 1225.1 square degrees and 2. 970% of the night sky, the three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is Her. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 32 segments, in mid-northern latitudes, Hercules is best observed from mid-Spring until the early part of the Fall season, culminating at midnight on June 13. The solar apex is the direction of the Suns motion with respect to the Local Standard of Rest and this is located within the constellation of Hercules, around coordinates Right Ascension 18h 00m and Declination 30°. The north pole of the coordinate system is located within this constellation at Right Ascension 18h 55m 01s. Hercules has no first or second magnitude stars, however, it does have several stars above magnitude 4. Alpha Herculis, traditionally called Rasalgethi, is a star system. The primary is a variable star, it is a bright giant with a minimum magnitude of 4. It has a diameter of roughly 400 solar diameters, the secondary, a spectroscopic binary that orbits the primary every 3600 years, is a blue-green hued star of magnitude 5.6. Its common name means the kneelers head, Beta Herculis, also called Kornephoros, is the brightest star in Hercules. It is a giant of magnitude 2.8,148 light-years from Earth. Deltoide 5512 is a double star divisible in amateur telescopes. The primary is a star of magnitude 3.1. The optical companion is of magnitude 8.2, gamma Herculis is also a double star divisible in small amateur telescopes. The primary is a giant of magnitude 3.8,195 light-years from Earth. The optical companion, widely separated, is 10th magnitude, zeta Herculis is a binary star that is becoming divisible in medium-aperture amateur telescopes, as the components widen to their peak in 2025
14.
Serpens
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Serpens is a constellation of the northern hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy and it is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput to the west and Serpens Cauda to the east. Between these two lies the constellation of Ophiuchus, the Serpent-Bearer. In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda. The brightest star in Serpens is the red giant star Alpha Serpentis, or Unukalhai, in Serpens Caput, also located in Serpens Caput are the naked-eye globular cluster Messier 5 and the naked-eye variables R Serpentis and Tau4 Serpentis. Part of the Milky Ways galactic plane passes through Serpens Cauda, the nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. In Greek mythology, Serpens represents a snake held by the healer Asclepius, represented in the sky by the constellation Ophiuchus, Asclepius once killed a snake, but the animal was subsequently resurrected after a second snake placed a revival herb on it before its death. As snakes shed their skin every year, they were known as the symbol of rebirth in ancient Greek society, although this is likely the logic for Serpens presence with Ophiuchus, the true reason is still not fully known. Sometimes, Serpens was depicted as coiling around Ophiuchus, but the majority of atlases showed Serpens passing either behind Ophiuchus body or between his legs. In some ancient atlases, the constellations Serpens and Ophiuchus were depicted as two separate constellations, although often they were shown as a single constellation. One notable figure to depict Serpens separately was Johann Bayer, thus, when Eugène Delporte established modern constellation boundaries in the 1920s, he elected to depict the two separately. However, this posed the problem of how to disentangle the two constellations, with Deporte deciding to split Serpens into two areas—the head and the tail—separated by the continuous Ophiuchus. These two areas known as Serpens Caput and Serpens Cauda, caput being the Latin word for head. In Chinese astronomy, most of the stars of Serpens represented part of a wall surrounding a marketplace, known as Tianshi, Serpens also contains a few Chinese constellations. Two stars in the tail represented part of Shilou, the tower with the market office, another star in the tail represented Liesi, jewel shops. One star in the head marked Tianru, the crown princes wet nurse, there were two serpent constellations in Babylonian astronomy, known as Mušḫuššu and Bašmu. It appears that Mušḫuššu was depicted as a hybrid of a dragon, a lion and a bird, Bašmu was a horned serpent and roughly corresponds to the Ὄφις constellation of Eudoxus of Cnidus on which the Ὄφις of Ptolemy is based. Serpens is the one of the 88 modern constellations to be split into two disconnected regions in the sky, Serpens Caput and Serpens Cauda
15.
North Pole
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The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is defined as the point in the Northern Hemisphere where the Earths axis of rotation meets its surface. The North Pole is the northernmost point on the Earth, lying diametrically opposite the South Pole and it defines geodetic latitude 90° North, as well as the direction of true north. At the North Pole all directions point south, all lines of longitude converge there, along tight latitude circles, counterclockwise is east and clockwise is west. The North Pole is at the center of the Northern Hemisphere, while the South Pole lies on a continental land mass, the North Pole is located in the middle of the Arctic Ocean amid waters that are almost permanently covered with constantly shifting sea ice. This makes it impractical to construct a permanent station at the North Pole, however, the Soviet Union, and later Russia, constructed a number of manned drifting stations on a generally annual basis since 1937, some of which have passed over or very close to the Pole. Since 2002, the Russians have also established a base, Barneo. This operates for a few weeks during early spring, studies in the 2000s predicted that the North Pole may become seasonally ice-free because of Arctic ice shrinkage, with timescales varying from 2016 to the late 21st century or later. The sea depth at the North Pole has been measured at 4,261 m by the Russian Mir submersible in 2007 and at 4,087 m by USS Nautilus in 1958. The nearest land is said to be Kaffeklubben Island, off the northern coast of Greenland about 700 km away. The nearest permanently inhabited place is Alert in the Qikiqtaaluk Region, Nunavut, Canada, around the beginning of the 20th century astronomers noticed a small apparent variation of latitude, as determined for a fixed point on Earth from the observation of stars. Part of this variation could be attributed to a wandering of the Pole across the Earths surface, the wandering has several periodic components and an irregular component. The component with a period of about 435 days is identified with the eight-month wandering predicted by Euler and is now called the Chandler wobble after its discoverer and it is desirable to tie the system of Earth coordinates to fixed landforms. Of course, given plate tectonics and isostasy, there is no system in all geographic features are fixed. Yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System. As early as the 16th century, many eminent people correctly believed that the North Pole was in a sea and it was therefore hoped that passage could be found through ice floes at favorable times of the year. Several expeditions set out to find the way, generally with whaling ships, one of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827 reached latitude 82°45′ North. In 1871 the Polaris expedition, a US attempt on the Pole led by Charles Francis Hall, another British Royal Navy attempt on the pole, part of the British Arctic Expedition, by Commander Albert H. Markham reached a then-record 83°2026 North in May 1876 before turning back. An 1879–1881 expedition commanded by US naval officer George W. DeLong ended tragically when their ship, over half the crew, including DeLong, were lost
16.
Northern Celestial Hemisphere
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The Northern Celestial Hemisphere or the Northern Sky is part of a rotating astronomical region in the sky. It is the hemisphere of the celestial sphere. The northern sky is that half of the sky, which is north of the sky equator. It can be overlooked from the North Pole, the farther south, the less is visible to the observer. In good visibility conditions, the observer encompasses around 2000 freely visible fixed stars, in the context of astronomical discussions or writing about celestial mapping, it may also simply then be referred to as the Northern Hemisphere. For the purpose of mapping, the sky is considered by astronomers as the inside of a sphere divided in two halves by the celestial equator. The Northern Sky or Northern Hemisphere is therefore that half of the sphere that is north of the celestial equator
17.
Ptolemy
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Claudius Ptolemy was a Greek writer, known as a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in the city of Alexandria in the Roman province of Egypt, wrote in Koine Greek, beyond that, few reliable details of his life are known. His birthplace has been given as Ptolemais Hermiou in the Thebaid in a statement by the 14th-century astronomer Theodore Meliteniotes. This is a very late attestation, however, and there is no reason to suppose that he ever lived elsewhere than Alexandria. Ptolemy wrote several treatises, three of which were of importance to later Byzantine, Islamic and European science. The first is the astronomical treatise now known as the Almagest, although it was entitled the Mathematical Treatise. The second is the Geography, which is a discussion of the geographic knowledge of the Greco-Roman world. The third is the treatise in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day. This is sometimes known as the Apotelesmatika but more known as the Tetrabiblos from the Greek meaning Four Books or by the Latin Quadripartitum. The name Claudius is a Roman nomen, the fact that Ptolemy bore it indicates he lived under the Roman rule of Egypt with the privileges and political rights of Roman citizenship. It would have suited custom if the first of Ptolemys family to become a citizen took the nomen from a Roman called Claudius who was responsible for granting citizenship, if, as was common, this was the emperor, citizenship would have been granted between AD41 and 68. The astronomer would also have had a praenomen, which remains unknown and it occurs once in Greek mythology, and is of Homeric form. All the kings after him, until Egypt became a Roman province in 30 BC, were also Ptolemies, abu Mashar recorded a belief that a different member of this royal line composed the book on astrology and attributed it to Ptolemy. The correct answer is not known”, Ptolemy wrote in Greek and can be shown to have utilized Babylonian astronomical data. He was a Roman citizen, but most scholars conclude that Ptolemy was ethnically Greek and he was often known in later Arabic sources as the Upper Egyptian, suggesting he may have had origins in southern Egypt. Later Arabic astronomers, geographers and physicists referred to him by his name in Arabic, Ptolemys Almagest is the only surviving comprehensive ancient treatise on astronomy. Ptolemy presented his models in convenient tables, which could be used to compute the future or past position of the planets. The Almagest also contains a catalogue, which is a version of a catalogue created by Hipparchus
18.
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
19.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
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Classical mythology
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Classical mythology or Greco-Roman mythology is both the body of and the study of myths from the ancient Greeks and Romans as they are used or transformed by cultural reception. Along with philosophy and political thought, mythology represents one of the major survivals of classical antiquity throughout later Western culture, the Greek word mythos refers to the spoken word or speech, but it also denotes a tale, story or narrative. Classical myths are also alluded to in scientific naming, particularly in astronomy, chemistry, and biology, and in the theory of Freud. During the Middle Ages and Renaissance, when Latin remained the dominant language in Europe for international educated discourse, mythological names almost always appeared in Latinized form. With the Greek revival of the 19th century, however, Greek names began to be used more often, classical mythology is a term often used to designate the myths belonging to the Greek and Roman traditions. A classical myth as it appears in later Western culture is usually a syncretism of various versions from both Greek and Latin sources. Greek myths were narratives related to ancient Greek religion, often concerned with the actions of gods and other supernatural beings, major sources for Greek myths include the Homeric epics, that is, the Iliad and the Odyssey, and the tragedies of Aeschylus, Sophocles, and Euripides. Known versions are preserved in sophisticated literary works shaped by the artistry of individuals and by the conventions of genre, or in vase painting. In these forms, mythological narratives often serve purposes that are not primarily religious, such as entertainment and even comedy, Roman myths have a dynamic relation to Roman historiography, as in the early books of Livys Ab urbe condita. The literary collection of Greco-Roman myths with the greatest influence on later Western culture was the Metamorphoses of the Augustan poet Ovid. The myths as they appear in popular culture of the 20th and 21st centuries often have only a tangential relation to the stories as told in ancient Greek and Latin literature
21.
Dionysus
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Dionysus is the god of the grape harvest, winemaking and wine, of ritual madness, fertility, theatre and religious ecstasy in ancient Greek religion and myth. Wine played an important role in Greek culture, and the cult of Dionysus was the religious focus for its unrestrained consumption. He may have been worshipped as early as c, 1500–1100 BC by Mycenean Greeks, traces of Dionysian-type cult have also been found in ancient Minoan Crete. His origins are uncertain, and his cults took many forms, some are described by ancient sources as Thracian, in some cults, he arrives from the east, as an Asiatic foreigner, in others, from Ethiopia in the South. He is a god of epiphany, the god that comes and his festivals were the driving force behind the development of Greek theatre. The earliest cult images of Dionysus show a male, bearded and robed. He holds a staff, tipped with a pine-cone and known as a thyrsus. Later images show him as a beardless, sensuous, naked or half-naked androgynous youth, in its fully developed form, his central cult imagery shows his triumphant, disorderly arrival or return, as if from some place beyond the borders of the known and civilized. His procession is made up of female followers and bearded satyrs with erect penises, some are armed with the thyrsus. The god himself is drawn in a chariot, usually by exotic beasts such as lions or tigers and this procession is presumed to be the cult model for the followers of his Dionysian Mysteries. He is also known as Bacchus, the adopted by the Romans. His thyrsus, sometimes wound with ivy and dripping with honey, is both a beneficent wand and a used to destroy those who oppose his cult and the freedoms he represents. As Eleutherios, his wine, music and ecstatic dance free his followers from self-conscious fear and care and those who partake of his mysteries are possessed and empowered by the god himself. The cult of Dionysus is also a cult of the souls, his maenads feed the dead through blood-offerings and he is sometimes categorised as a dying-and-rising god. Some scholars believe that Dionysus is a syncretism of a local Greek nature deity, Dionysus had a strange birth that evokes the difficulty in fitting him into the Olympian pantheon. His mother was a woman, Semele, the daughter of king Cadmus of Thebes, and his father was Zeus. Zeus wife, Hera, discovered the affair while Semele was pregnant, appearing as an old crone, Hera befriended Semele, who confided in her that Zeus was the actual father of the baby in her womb. Hera pretended not to believe her, and planted seeds of doubt in Semeles mind, curious, Semele demanded of Zeus that he reveal himself in all his glory as proof of his godhood
22.
Ariadne
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Ariadne, in Greek mythology, was the daughter of Minos, King of Crete, Son of Zeus and his queen Pasiphaë, daughter of Helios. She is mostly associated with mazes and labyrinths because of her involvement in the myths of the Minotaur and her father put her in charge of the labyrinth where sacrifices were made as part of reparations, later, she helped Theseus overcome the Minotaur and save the potential sacrificial victims. In other stories, she became the bride of the god Dionysus, since ancient Greek myths are passed down through oral tradition, many variations of this and other myths exist. According to an Athenian version of the legend, Minos attacked Athens after his son was killed there, the Athenians asked for terms, and were required to sacrifice seven young men and seven maidens to the Minotaur every seven or nine years. One year, the party included Theseus, the son of King Aegeus. Ariadne fell in love at first sight, and helped him by giving him a sword and a ball of thread, so that he could find his way out of the Minotaurs labyrinth. She eloped with Theseus after he achieved his goal, but according to Homer he had no joy of her, for ere that, Artemis slew her in seagirt Dia because of the witness of Dionysus. Homer does not expand on the nature of Dionysuss accusation, in Hesiod and most other accounts, Theseus abandoned Ariadne sleeping on Naxos, and Dionysus rediscovered and wedded her. The vase-painters of Athens often showed Athena leading Theseus from the sleeping Ariadne to his ship. With Dionysus, she was the mother of Oenopion, the personification of wine, Staphylus, Thoas, Peparethus, Phanus, Eurymedon, Enyeus, Ceramus, Maron, Euanthes, Latramys and her wedding diadem was set in the heavens as the constellation Corona Borealis. Ariadne remained faithful to Dionysus but was killed by Perseus at Argos. In other myths she hanged herself from a tree, like Erigone and the hanging Artemis, some scholars have posited, due to her thread-spinning and winding associations, that she was a weaving goddess, like Arachne, supporting this theory with the mytheme of the Hanged Nymph. Dionysus descended into Hades and brought her and his mother Semele back and they then joined the gods in Olympus. Karl Kerenyi and Robert Graves theorize that Ariadne was a Great Goddess of Crete, Kerenyi notes a Linear B inscription from Knossos, to all the gods, honey. To the mistress of the honey in equal amounts, suggesting to him that the Mistress of the Labyrinth was a Great Goddess in her own right. Professor Barry Powell has suggested she was Minoan Cretes Snake Goddess, in a kylix by the painter Aison Theseus drags the Minotaur from a temple-like labyrinth, but the goddess who attends him, in this Attic representation, is Athena. Theseus, attempting to secure the ship, was swept out to sea. The Cypriote women cared for Ariadne, who died in childbirth and was memorialized in a shrine, Theseus, overcome with grief upon his return, left money for sacrifices to Ariadne and ordered two cult images, one of silver and one of bronze, set up
23.
Corona Australis
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Corona Australis or Corona Austrina is a constellation in the Southern Celestial Hemisphere. Its Latin name means southern crown, and it is the counterpart of Corona Borealis. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, the Ancient Greeks saw Corona Australis as a wreath rather than a crown and associated it with Sagittarius or Centaurus. Other cultures have likened the pattern to a turtle, ostrich nest, although fainter than its namesake, the oval- or horseshoe-shaped pattern of its brighter stars renders it distinctive. Alpha and Beta Coronae Australis are the two brightest stars with an apparent magnitude of around 4.1, Epsilon Coronae Australis is the brightest example of a W Ursae Majoris variable in the southern sky. Within it are stars at the earliest stages of their lifespan, the variable stars R and TY Coronae Australis light up parts of the nebula, which varies in brightness accordingly. The name of the constellation was entered as Corona Australis when the International Astronomical Union established the 88 modern constellations in 1922, in 1932, the name was instead recorded as Corona Austrina when the IAUs commission on notation approved a list of four-letter abbreviations for the constellations. Although the four-letter abbreviations were repealed in 1955, this name has persisted alongside the original. The IAU presently uses Corona Australis exclusively, Corona Australis is a small constellation bordered by Sagittarius to the north, Scorpius to the west, Telescopium to the south, and Ara to the southwest. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is CrA, the official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 17h 58. 3m and 19h 19. 0m, while the coordinates are between −36. 77° and −45. 52°. Covering 128 square degrees, Corona Australis culminates at midnight around the 30th of June, while not a bright constellation, Corona Australis is nonetheless distinctive due to its easily identifiable pattern of stars, which has been described as horseshoe- or oval-shaped. Though it has no stars brighter than 4th magnitude, it still has 21 stars visible to the unaided eye. Nicolas Louis de Lacaille used the Greek letters Alpha through to Lambda to label the most prominent eleven stars in the constellation, the only star in the constellation to have received a name is Alfecca Meridiana or Alpha CrA. The name combines the Arabic name of the constellation with the Latin for southern, in Arabic, Alfecca means break, and refers to the shape of both Corona Australis and Corona Borealis. Also called simply Meridiana, it is a main sequence star located 130 light years away from Earth, with an apparent magnitude of 4.10. A rapidly rotating star, it spins at almost 200 km per second at its equator, like the star Vega, it has excess infrared radiation, which indicates it may be ringed by a disk of dust. It is currently a star, but will eventually evolve into a white dwarf, currently, it has a luminosity 31 times greater
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R Coronae Borealis
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R Coronae Borealis is a peculiar low-mass yellow supergiant star, and is the prototype of the rare RCB class of variable stars, which fade by several magnitudes at irregular intervals. Over successive months it gradually returns to its brightness, giving it the nickname Fade-Out star. The variability of R CrB was discovered by the English astronomer Edward Pigott in 1795 and it was known as Variabilis Coronae, Variable of Corona. In 1935 it was the first star shown to have a different chemical composition than the sun via spectral analysis, R Coronae Borealis is a variable star and the prototype of its class. It is one of only two R Coronae Borealis variables bright enough to be seen with the eye, along with RY Sagittarii. Much of the time it shows variations of around a tenth of a magnitude with poorly defined periods that have reported as 40 and 51 days. These correspond to the first overtone and fundamental radial pulsation modes for an extreme helium star slightly under one M☉, at irregular intervals a few years or decades apart R Coronae Borealis fades from its normal brightness near 6th magnitude for a period of months or sometimes years. There is no fixed minimum, but the star can become fainter than 15th magnitude in the visual range, the fading is less pronounced at longer wavelengths. Typically the star starts to return to maximum brightness almost immediately from its minimum and this irregular fading is the defining characteristic of the R Coronae Borealis variables and is thought to be due to the condensation of carbon into soot surrounding the star. In August 2007, R Coronae Borealis began a fade to an unprecedented minimum and it fell to 14th magnitude in 33 days, then continued to fade slowly, dropping below 15th magnitude in June 2009. It then began a slow rise, not reaching 12th magnitude until late 2011. This was a deep and exceptional long minimum, longer even than the deep five year minimum of 1962-7. However, R Coronae Borealis then faded again to near 15th magnitude, in late 2014, R Coronae Borealis brightened quickly to 7th magnitude but then began to fade again. As of May 2015 it is around 8th magnitude, R Coronae Borealis at maximum light shows the spectrum clearly of a late F or early G yellow supergiant, but with marked peculiarities. Hydrogen lines are weak or absent, while carbon lines and molecular bands of cyanogen, helium lines and metals such as calcium are also present as expected. The spectrum is variable, most obviously during the brightness fades, the normal absorption spectrum is replaced by emission lines, especially HeI, CaII, NaI, and other metals. The lines are very narrow at this stage. Helium emission lines sometimes show P Cygni profiles, in deep minima, many of the metal lines disappear although the Ca doublet remains strong
25.
R Coronae Borealis variable
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An R Coronae Borealis variable is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation, and one irregular unpredictably sudden fading by 1 to 9 magnitudes. The prototype star R Coronae Borealis was discovered by the English amateur astronomer Edward Pigott in 1795, since then, only about 100 RCB variables have been identified, making this class a very rare kind of star. The fading is caused by condensation of carbon to soot, making the star fade in visible light while measurements in infrared light exhibit no real luminosity decrease. R Coronae Borealis variables are typically supergiant stars in the spectral classes F and G, with typical C2 and CN molecular bands, there is a considerable variation in spectrum between various RCB specimens. Most of the stars with known spectrum are either F to G class supergiants, three of the stars are however of the blue B type, for example VZ Sagittarii. Four stars are unusually and inexplicably poor in iron absorption lines in the spectrum, the constant features are prominent Carbon lines, strong atmospheric Hydrogen deficiencies, and obviously the intermittent fadings. The DY Persei variables have been considered a sub-class of R CrB variable, although they are less luminous carbon-rich AGB stars, the 20 radii model requires a large and thereby long-time buildup of the obstructing dust cloud, making the fast light decline hard to comprehend. The formation of the stars themselves is also unclear, standard stellar evolution models do not produce large luminous stars with essentially zero hydrogen. The two main theories to explain these stars are both somewhat exotic, perhaps befitting such rare stars, in one, a merger occurs between two white dwarf stars, one a Helium white dwarf and the other a carbon-oxygen white dwarf. White dwarfs are naturally lacking in hydrogen and the resultant star would also lack that element and it is possible that the diversity of R CrB stars is caused by a diversity of formation mechanisms, relating them to extreme helium stars and hydrogen-deficient carbon stars. This list contains all the R CrB stars listed in the GCVS, DY Persei is not included although it may be a related type of variable. Clayton, from SAO/NASA Astrophysics Data System Variable Star of the Month, January,2000, R Coronae Borealis, at the AAVSO website
26.
Nova
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A nova or classical nova is an astronomical event that causes the sudden appearance of a bright new star, that slowly fades from view over several weeks or many months. Novae should not be confused with more energetic astronomical phenomena known as supernovae. Several main sub-classes of novae exist, based on their many different scenarios, being classical novae, recurrent novae, dwarf novae and they are together under a group of variable stars collectively known as cataclysmic variable stars, which share some common properties as close binary systems. Classical novae eruptions are the most common type of novae and they are likely created in a close binary star system consisting of a white dwarf and either a main sequence, sub-giant or red giant star. This mostly hydrogen atmosphere is heated from the hot white dwarf star, which eventually reaches a critical temperature. A few novae produce short-lived nova remnants, lasting several centuries. Recurrent nova processes are the same as the classical nova, except that the ignition can be repeated because the companion star can again feed the dense atmosphere of the white dwarf. Occurrences of novae mostly occur in the sky along the path of the Milky Way, however, it is also quite possible for them to appear anywhere in the sky. They are far more frequent than galactic supernovae, presently averaging about ten per year, the majority are found telescopically, with few reaching naked-eye visibility, perhaps averaging about once every year to eighteen months. Novae reaching 1st or 2nd magnitude occur only several times per century, the last bright nova was V1369 Centauri reaching 3.3 magnitude on 14 December 2013. During the 16th century, astronomer Tycho Brahe observed the supernova SN1572 in the constellation Cassiopeia and he described it in his book De nova stella, giving rise to the name nova. In this work he argued that an object should be seen to move relative to the fixed stars. Though this was a supernova and not a nova, the terms were considered interchangeable until the 1930s, after this, novae were classified as classical novae to distinguishing them from supernovae, as their causes and energies were though to be different based soley in the observational evidence. Evolution of potential novae begins with two main stars in a binary system. One of the two evolves into a red giant leaving its remnant white dwarf core in orbit with the remaining star, the second star—which may be either a main sequence star or an aging giant—begins to shed its envelope onto its white dwarf companion when it overflows its Roche lobe. As a result, the white dwarf captures matter in an accretion disk steadily from the outer atmosphere. As the white dwarf consists of matter, so the accreted hydrogen does not inflate. Rapid, an all at once, uncontrolled fusion occurs when the temperature of this layer reaches ~20 million Kelvins
27.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found
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Galaxy cluster
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They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium, the ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as clusters, which are structures of stars within galaxies, or with globular clusters. Small aggregates of galaxies are referred to as groups of galaxies rather than clusters of galaxies, the groups and clusters can themselves cluster together to form superclusters. Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, a very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-CL J2106-5844, using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters. Galaxy clusters typically have the properties, They contain 100 to 1,000 galaxies, hot X-ray- emitting gas. Details are described in the Composition section, the distribution of the three components is approximately the same in the cluster. They have total masses of 1014 to 1015 solar masses and they typically have a diameter from 2 to 10 Mpc. The spread of velocities for the galaxies is about 800–1000 km/s. There are three components of a galaxy cluster. They are tabulated below, Stars, Star clusters, Galaxies, Galaxy clusters, Super clusters Abell catalogue Intracluster medium List of Abell clusters
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International Astronomical Union
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The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II
30.
Equatorial coordinate system
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The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. The origin at the center of the Earth means the coordinates are geocentric, a right-handed convention means that coordinates are positive toward the north and toward the east in the fundamental plane. This description of the orientation of the frame is somewhat simplified. A slow motion of Earths axis, precession, causes a slow, continuous turning of the system westward about the poles of the ecliptic. Superimposed on this is a motion of the ecliptic. In order to fix the primary direction, these motions necessitate the specification of the equinox of a particular date, known as an epoch. The three most commonly used are, Mean equinox of an epoch is a fixed standard direction. Mean equinox of date is the intersection of the ecliptic of date with the mean equator, commonly used in planetary orbit calculation. True equinox of date is the intersection of the ecliptic of date with the true equator and this is the actual intersection of the two planes at any particular moment, with all motions accounted for. A position in the coordinate system is thus typically specified true equinox and equator of date, mean equinox and equator of J2000.0. Note that there is no mean ecliptic, as the ecliptic is not subject to small periodic oscillations, a stars spherical coordinates are often expressed as a pair, right ascension and declination, without a distance coordinate. The direction of distant objects is the same for all observers. Telescopes equipped with equatorial mounts and setting circles employ the equatorial coordinate system to find objects, setting circles in conjunction with a star chart or ephemeris allow the telescope to be easily pointed at known objects on the celestial sphere. The declination symbol δ, measures the distance of an object perpendicular to the celestial equator, positive to the north. For example, the celestial pole has a declination of +90°. The origin for declination is the equator, which is the projection of the Earths equator onto the celestial sphere. Declination is analogous to terrestrial latitude, the right ascension symbol α, measures the angular distance of an object eastward along the celestial equator from the vernal equinox to the hour circle passing through the object. The vernal equinox point is one of the two where the ecliptic intersects the celestial equator, there are = 15° in one hour of right ascension, 24h of right ascension around the entire celestial equator
31.
Beta Coronae Borealis
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Beta Coronae Borealis, also named Nusakan, is a binary star in the constellation of Corona Borealis. It appears to the eye to be a single star and is the second-brightest star in its constellation. It is 112±3 light-years from the Sun and has an apparent visual magnitude varies between 3.65 and 3.72. β Coronae Borealis is the systems Bayer designation and it bore the traditional name Nusakan. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalogue, the WGSN approved the name Nusakan for this star on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names. Consequently, Beta Coronae Borealis itself is known as 貫索三, Beta Coronae Borealis was first announced to be a binary star in 1907, based on spectroscopic observations at Lick Observatory, J. B. Cannon published an orbit in 1914, finding a period of 40.9 days, later spectroscopic investigations by F. J. Neubauer at Lick, published in 1944, found a period of 10.5 years, with no evidence for the 41-day periodicity. Antoine Labeyrie and his coworkers resolved the pair by speckle interferometry in 1973, the pair was also observed visually by Coteau in 1973. A number of orbits were subsequently published using visual and speckle-interferometric observations, in 1999, Söderhjelm published an orbit using speckle-interferometric data together with Hipparcos observations. Neubauers 1944 work found a variation in the radial velocity of Beta Coronae Borealis with a periodicity of 320 days, suggesting the presence of a third, lighter. This study also found very weak evidence for the presence of a companion with a shorter, 21-day, period, the brighter component is a Rapidly oscillating Ap star, with a period of 16.2 minutes. Of spectral type A5V with a temperature of around 7980 K. The smaller star is of spectral type F2V with a temperature of around 6750 K. The system is around 530 million years old
32.
Johann Bayer
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Johann Bayer was a German lawyer and uranographer. He was born in Rain, Lower Bavaria, in 1572, Bayer had several interests outside his work, including archaeology and mathematics. However, he is known for his work in astronomy. He remained unmarried and died in 1625, Bayer is most famous for his star atlas Uranometria Omnium Asterismorum, which was first published in 1603 in Augsburg and dedicated to two prominent local citizens. This was the first atlas to cover the entire celestial sphere and it was based upon the work of Tycho Brahe and may have borrowed from Alessandro Piccolominis 1540 star atlas, De le stelle fisse, although Bayer included an additional 1,000 stars. The Uranometria introduced a new system of star designation which has known as the Bayer designation. Bayers atlas included twelve new constellations invented a few years earlier to fill in the far south of the night sky, the crater Bayer on the Moon is named after him. Julius Schiller Bayer designation Full digital facsimile, Linda Hall Library
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Celestial cartography
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Measuring the position and light of charted objects requires a variety of instruments and techniques. Uranographers have historically produced planetary position tables, star tables and star maps for use by amateur and professional astronomers. More recently computerized star maps have been compiled, and automated positioning of telescopes is accomplished using databases of stars, the word uranography derived from the Greek ουρανογραφια through the Latin uranographia. In Renaissance times, Uranographia was used as the title of various celestial atlases. During the 19th century, uranography was defined as the description of the heavens, elijah H. Burritt re-defined it as the geography of the heavens. The German word for uranography is Uranographie, the French is uranographie, a determining fact source for drawing star charts is naturally a star table. C, AD150, Almagest – contains the last known star table from antiquity, C.964, Book of the Fixed Stars, Arabic version of the Almagest by al-Sufi. 1627, Rudolphine Tables – contains the first West Enlightenment star table,1690, Prodromus Astronomiae – by Johannes Hevelius for his Firmamentum Sobiescanum,1,564 stars. 1729, Britannic Catalogue – by John Flamsteed for his Atlas Coelestis,1903, Bonner Durchmusterung – by Friedrich Wilhelm Argelander and collaborators, circa 460,000 stars. 15th century BC – The ceiling of the tomb TT71 for the Egyptian architect and minister Senenmut, poeticon astronomicon, allegedly by Gaius Julius Hyginus 1092 – Xin Yi Xiang Fa Yao, by Su Song, a horological treatise which had the earliest existent star maps in printed form. True Visual Magnitude Photographic Star Atlas, pasachoff, Wil Tirion charts SkyGX – Christopher Watson The Great Atlas of the Sky – Piotr Brych. 100,000 Stars Cartes du Ciel Celestia 3D Galaxy Map CyberSky GoSkyWatch Planetarium Google Sky KStars Stellarium SKY-MAP. ORG SkyMap Online WorldWide Telescope XEphem, monthly star maps for every location on Earth Easy to use monthly star maps for northern and southern hemispheres. Helpful target lists for naked eye, binocular, or telescope viewing, collection of rare star atlases, charts, and maps available in full digital facsimile at Linda Hall Library. The Great Atlas of the Sky – worlds largest printed atlas of the sky, navigable online map of the stars, Stellarmap. com. The Digital Collections of the Linda Hall Library include, Astronomy, Star Atlases, Charts, and Maps, Astronomy, Selected Images, a collection of high-resolution star map images. History of Cosmology, Views of the Stars, high-resolution scans of prints relating to the study of the structure of the cosmos, EDSM, an external community supporting the recording of exploration data in Elite, Dangerous. GalNet, the community news source for Elite, Dangerous galactic activity, Community Goal, More Imperial Warships. Article citing the discovery of the lost Jaques station
. Bibcode:2014ApJ...792...65P. doi:10.1088/0004-637X/792/1/65. 65.
Media related to Corona Borealis at Wikimedia Commons
