Apparent magnitude
The apparent magnitude of an astronomical object is a number, a measure of its brightness as seen by an observer on Earth. The magnitude scale is logarithmic. A difference of 1 in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The brighter an object appears, the lower its magnitude value, with the brightest astronomical objects having negative apparent magnitudes: for example Sirius at −1.46. 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 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 simply as V, as in "mV = 15" or "V = 15" to describe a 15th-magnitude object; 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 night sky were said to be of first magnitude, whereas the faintest were of sixth magnitude, the limit of human visual perception. Each grade of magnitude was considered twice the brightness of the following grade, although that ratio was subjective as no photodetectors existed; this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is believed to have originated with Hipparchus. In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star, 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today; this implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1. This figure, the fifth root of 100, became known as Pogson's Ratio; the zero point of Pogson's scale was defined by assigning Polaris a magnitude of 2. Astronomers discovered that Polaris is variable, so they switched to Vega as the standard reference star, assigning the brightness of Vega as the definition of zero magnitude at any specified wavelength.
Apart from small corrections, the brightness of Vega still serves as the definition of zero magnitude for visible and near infrared wavelengths, where its spectral energy distribution approximates that of a black body for a temperature of 11000 K. However, with the advent of infrared astronomy it was revealed that Vega's radiation includes an Infrared excess due to a circumstellar 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 magnitude 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, as a function of wavelength, can be computed. Small deviations are specified between systems using measurement apparatuses developed independently so that data obtained by different astronomers can be properly compared, but of greater practical importance is the definition of magnitude not at a single wavelength but applying to the response of standard spectral filters used in photometry over various wavelength bands.
With the modern magnitude systems, brightness over a wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30; the brightness of Vega is exceeded by four stars in the night sky at visible wavelengths as well as the bright planets Venus and Jupiter, these must be described by negative magnitudes. For example, the brightest star of the celestial sphere, has an apparent magnitude of −1.4 in the visible. Negative magnitudes for other bright astronomical objects can be found in the table below. Astronomers have developed other photometric zeropoint systems as alternatives to the Vega system; the most used is the AB magnitude system, in which photometric zeropoints are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zeropoint is defined such that an object's AB and Vega-based magnitudes will be equal in the V filter band.
As the amount of light received by a telescope is reduced by transmission through the Earth's atmosphere, any measurement of apparent magnitude is corrected for what it would have been as seen from above the atmosphere. 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 100. Therefore, the apparent magnitude m, in the spectral band x, would be given by m x = − 5 log 100 , more expressed in terms of common logarithms as m x
Black hole
A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole; the boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways, a black hole acts like an ideal black body. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass; this temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it impossible to observe. Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.
The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; the discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. Black holes of stellar mass are expected to form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus. Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light.
Matter that falls onto a black hole can form an external accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location; such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses. On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves, which represented the first observation of a black hole merger; as of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope in 2017 of the supermassive black hole in Messier 87's galactic centre.
Larry Kimura, a Hawaiian language professor at the University of Hawaii at Hilo, named the hole Pōwehi—a Hawaiian phrase referring to an "embellished dark source of unending creation." The idea of a body so massive that light could not escape was proposed by astronomical pioneer and English clergyman John Michell in a letter published in November 1784. Michell's simplistic calculations assumed that such a body might have the same density as the Sun, concluded that such a body would form when a star's diameter exceeds the Sun's by a factor of 500, the surface escape velocity exceeds the usual speed of light. Michell noted that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies. Scholars of the time were excited by the proposal that giant but invisible stars might be hiding in plain view, but enthusiasm dampened when the wavelike nature of light became apparent in the early nineteenth century. If light were a wave rather than a "corpuscle", it became unclear what, if any, influence gravity would have on escaping light waves.
Modern relativity discredits Michell's notion of a light ray shooting directly from the surface of a supermassive star, being slowed down by the star's gravity and free-falling back to the star's surface. In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties; this solution had a peculiar behaviour at what is now called the Schwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time. In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates, although it took until 1933 for Georges Lemaître to realize that this meant the singularity at the Schwarzschild radius was a non-physical coordinate singularity.
Arthur Eddington did however comment on the possibility of a star with mass c
Unicorn
The unicorn is a legendary creature, described since antiquity as a beast with a single large, spiraling horn projecting from its forehead. The unicorn was depicted in ancient seals of the Indus Valley Civilization and was mentioned by the ancient Greeks in accounts of natural history by various writers, including Ctesias, Pliny the Younger and Cosmas Indicopleustes; the Bible describes an animal, the re'em, which some versions translate as unicorn. In European folklore, the unicorn is depicted as a white horse-like or goat-like animal with a long horn and cloven hooves. In the Middle Ages and Renaissance, it was described as an wild woodland creature, a symbol of purity and grace, which could be captured only by a virgin. In the encyclopedias, its horn was said to have the power to render poisoned water potable and to heal sickness. In medieval and Renaissance times, the tusk of the narwhal was sometimes sold as unicorn horn. In the twenty-first century, the unicorn holds a place in popular culture.
It is used as a symbol of fantasy or rarity. A number of seals depicting unicorns have been found from the Indus Valley Civilisation; these have been interpreted as representations of aurochs—a type of large wild cattle that inhabited Europe and North Africa—or derivatives of aurochs, because the animal is always shown in profile, indicating there may have supposed to have been another horn, not seen. Unicorns are not found in Greek mythology, but rather in the accounts of natural history, for Greek writers of natural history were convinced of the reality of unicorns, which they believed lived in India, a distant and fabulous realm for them; the earliest description is from Ctesias, who in his book Indika described them as wild asses, fleet of foot, having a horn a cubit and a half in length, colored white and black. Ctesias got his information while living in Persia. Unicorns on a relief sculpture have been found at the ancient Persian capital of Persepolis in Iran. Aristotle must be following Ctesias when he mentions two one-horned animals, the oryx and the so-called "Indian ass".
Strabo says. Pliny the Elder mentions the oryx and an Indian ox as one-horned beasts, as well as "a fierce animal called the monoceros which has the head of the stag, the feet of the elephant, the tail of the boar, while the rest of the body is like that of the horse. In On the Nature of Animals, quoting Ctesias, adds that India produces a one-horned horse, says that the monoceros was sometimes called cartazonos, which may be a form of the Arabic karkadann, meaning "rhinoceros". Cosmas Indicopleustes, a merchant of Alexandria who lived in the 6th century, made a voyage to India and subsequently wrote works on cosmography, he gives a description of a unicorn based on four brass figures in the palace of the King of Ethiopia. He states, from report; when it finds itself pursued and in danger of capture, it throws itself from a precipice, turns so aptly in falling, that it receives all the shock upon the horn, so escapes safe and sound". A one-horned animal is found on some seals from the Indus Valley Civilisation.
Seals with such a design are thought to be a mark of high social rank. Medieval knowledge of the fabulous beast stemmed from biblical and ancient sources, the creature was variously represented as a kind of wild ass, goat, or horse; the predecessor of the medieval bestiary, compiled in Late Antiquity and known as Physiologus, popularized an elaborate allegory in which a unicorn, trapped by a maiden, stood for the Incarnation. As soon as the unicorn sees her, it falls asleep; this became a basic emblematic tag that underlies medieval notions of the unicorn, justifying its appearance in every form of religious art. Interpretations of the unicorn myth focus on the medieval lore of beguiled lovers, whereas some religious writers interpret the unicorn and its death as the Passion of Christ; the myths refer to a beast with one horn. The unicorn figured in courtly terms: for some 13th-century French authors such as Thibaut of Champagne and Richard de Fournival, the lover is attracted to his lady as the unicorn is to the virgin.
With the rise of humanism, the unicorn acquired more orthodox secular meanings, emblematic of chaste love and faithful marriage. It plays this role in Petrarch's Triumph of Chastity, on the reverse of Piero della Francesca's portrait of Battista Strozzi, paired with that of her husband Federico da Montefeltro, Bianca's triumphal car is drawn by a pair of unicorns; the Throne Chair of Denmark is made of "unicorn horns" – certainly narwhal tusks. The same material was used for ceremonial cups because the unicorn's horn continued to be believed to neutralize poison, following classical authors; the unicorn, tamable only by a virgin woman, was well established in medieval lore by the time Marco Polo described them as "scarcely smaller than elephants. They have the hair of feet like an elephant's, they ha
Messier object
The Messier objects are a set of 110 astronomical objects cataloged by the French astronomer Charles Messier in his Catalogue des Nébuleuses et des Amas d'Étoiles. Because Messier was interested in finding only comets, he created a list of non-comet objects that frustrated his hunt for them; the compilation of this list, in collaboration with his assistant Pierre Méchain, is known as the Messier catalogue. This catalogue of objects is one of the most famous lists of astronomical objects, many Messier objects are still referenced by their Messier number; the catalogue includes some astronomical objects that can be observed from Earth's Northern Hemisphere such as deep-sky objects, a characteristic which makes the Messier objects popular targets for amateur astronomers. A preliminary version first appeared in the Memoirs of the French Academy of Sciences in 1771, the last item was added in 1966 by Kenneth Glyn Jones, based on Messier's observations; the first version of Messier's catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris.
In addition to his own discoveries, this version included objects observed by other astronomers, with only 17 of the 45 objects being Messier's. By 1780 the catalogue had increased to 80 objects; the final version of the catalogue containing 103 objects was published in 1781 in the Connaissance des Temps for the year 1784. However, due to what was thought for a long time to be the incorrect addition of Messier 102, the total number remained 102. Other astronomers, using side notes in Messier's texts filled out the list up to 110 objects; the catalogue consists of a diverse range of astronomical objects, ranging from star clusters and nebulae to galaxies. For example, Messier 1 is a supernova remnant, known as the Crab Nebula, the great spiral Andromeda Galaxy is M31. Many further inclusions followed in the next century when the first addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding Messier's side note in his 1781 edition exemplar of the catalogue. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, M110 by Kenneth Glyn Jones in 1967.
The first edition of 1771 covered 45 objects numbered M1 to M45. The total list published by Messier in 1781 contained 103 objects, but the list was expanded through successive additions by other astronomers, motivated by notes in Messier's and Méchain's texts indicating that at least one of them knew of the additional objects; 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 catalog. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, M110 by Kenneth Glyn Jones in 1967. M102 was observed by Méchain. Méchain concluded that this object was a re-observation of M101, though some sources suggest that the object Méchain observed was the galaxy NGC 5866 and identify that as M102. Messier's final catalogue was included in the Connaissance des Temps for 1784, the French official yearly publication of astronomical ephemerides; these objects are still known by their "Messier number" from this list.
Messier did his astronomical work at the Hôtel de Cluny, in Paris, France. The list he compiled contains only objects found in the sky area he could observe: from the north celestial pole to a celestial latitude of about −35.7°. He did not observe or list objects visible only from farther south, such as the Large and Small Magellanic Clouds; the Messier catalogue comprises nearly all the most spectacular examples of the five types of deep-sky object – diffuse nebulae, planetary nebulae, open clusters, globular clusters, galaxies – visible from European latitudes. Furthermore all of the Messier objects are among the closest to Earth in their respective classes, which makes them studied with professional class instruments that today can resolve small and visually spectacular details in them. A summary of the astrophysics of each Messier object can be found in the Concise Catalog of Deep-sky Objects. Since these objects could be observed visually with the small-aperture refracting telescope used by Messier to study the sky, they are among the brightest and thus most attractive astronomical objects observable from Earth, are popular targets for visual study and astrophotography available to modern amateur astronomers using larger aperture equipment.
In early spring, astronomers sometimes gather for "Messier marathons", when all of the objects can be viewed over a single night. Lists of astronomical objects List of Messier objects Caldwell catalogue Deep-sky object Herschel 400 Catalogue New General Catalogue SEDS Messier Database Charles Messier Charles Messier's Catalog of Nebulae and Star Clusters History of the Messier Catalog Interactive Messier Catalog Greenhawk Observatory Listing of Copyright-free Images of all Messier Objects CCD Images of Messier Objects 12 Dimensional String Messier Gallery The Messier Catalogue Merrifield, Mike. "Messier Objects". Deep Sky Videos. Brady Haran. Messier Objects at Constellation Guide
Variable star
A variable star is a star whose brightness as seen from Earth fluctuates. This variation may be caused by a change in emitted light or by something blocking the light, so variable stars are classified as either: Intrinsic variables, whose luminosity changes. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth. Many most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle. An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti pulsated in a cycle taking 11 months; this discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught.
In this way, the discovery of variable stars contributed to the astronomical revolution of the sixteenth and early seventeenth centuries. The second variable star to be described was the eclipsing variable Algol, by Geminiano Montanari in 1669. Chi Cygni was identified in 1686 by G. Kirch R Hydrae in 1704 by G. D. Maraldi. By 1786 ten variable stars were known. John Goodricke himself discovered Beta Lyrae. Since 1850 the number of known variable stars has increased especially after 1890 when it became possible to identify variable stars by means of photography; the latest edition of the General Catalogue of Variable Stars lists more than 46,000 variable stars in the Milky Way, as well as 10,000 in other galaxies, over 10,000'suspected' variables. The most common kinds of variability involve changes in brightness, but other types of variability occur, in particular changes in the spectrum. By combining light curve data with observed spectral changes, astronomers are able to explain why a particular star is variable.
Variable stars are analysed using photometry, spectrophotometry and spectroscopy. Measurements of their changes in brightness can be plotted to produce light curves. For regular variables, the period of variation and its amplitude can be well established. Peak brightnesses in the light curve are known as maxima. Amateur astronomers can do useful scientific study of variable stars by visually comparing the star with other stars within the same telescopic field of view of which the magnitudes are known and constant. By estimating the variable's magnitude and noting the time of observation a visual lightcurve can be constructed; the American Association of Variable Star Observers collects such observations from participants around the world and shares the data with the scientific community. From the light curve the following data are derived: are the brightness variations periodical, irregular, or unique? What is the period of the brightness fluctuations? What is the shape of the light curve? From the spectrum the following data are derived: what kind of star is it: what is its temperature, its luminosity class? is it a single star, or a binary? does the spectrum change with time?
Changes in brightness may depend on the part of the spectrum, observed if the wavelengths of spectral lines are shifted this points to movements strong magnetic fields on the star betray themselves in the spectrum abnormal emission or absorption lines may be indication of a hot stellar atmosphere, or gas clouds surrounding the star. In few cases it is possible to make pictures of a stellar disk; these may show darker spots on its surface. Combining light curves with spectral data gives a clue as to the changes that occur in a variable star. For example, evidence for a pulsating star is found in its shifting spectrum because its surface periodically moves toward and away from us, with the same frequency as its changing brightness. About two-thirds of all variable stars appear to be pulsating. In the 1930s astronomer Arthur Stanley Eddington showed that the mathematical equations that describe the interior of a star may lead to instabilities that cause a star to pulsate; the most common type of instability is related to oscillations in the degree of ionization in outer, convective layers of the star.
Suppose the star is in the swelling phase. Its outer layers expand; because of the decreasing temperature the degree of ionization decreases. This makes the gas more transparent, thus makes it easier for the star to radiate its energy; this in turn will make the star start to contract. As the gas is thereby compressed, it is heated and the degree of ionization again increases. Thi
South Pole
The South Pole known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of Earth and lies on the opposite side of Earth from the North Pole. Situated on the continent of Antarctica, it is the site of the United States Amundsen–Scott South Pole Station, established in 1956 and has been permanently staffed since that year; the Geographic South Pole is distinct from the South Magnetic Pole, the position of, defined based on Earth's magnetic field. The South Pole is at the center of the Southern Hemisphere. For most purposes, the Geographic South Pole is defined as the southern point of the two points where Earth's axis of rotation intersects its surface. However, Earth's axis of rotation is subject to small "wobbles", so this definition is not adequate for precise work; the geographic coordinates of the South Pole are given as 90°S, since its longitude is geometrically undefined and irrelevant.
When a longitude is desired, it may be given as 0°. At the South Pole, all directions face north. For this reason, directions at the Pole are given relative to "grid north", which points northwards along the prime meridian. Along tight latitude circles, clockwise is east, counterclockwise is west, opposite to the North Pole; the Geographic South Pole is located on the continent of Antarctica. It sits atop a featureless, barren and icy plateau at an altitude of 2,835 metres above sea level, is located about 1,300 km from the nearest open sea at Bay of Whales; the ice is estimated to be about 2,700 metres thick at the Pole, so the land surface under the ice sheet is near sea level. The polar ice sheet is moving at a rate of 10 metres per year in a direction between 37° and 40° west of grid north, down towards the Weddell Sea. Therefore, the position of the station and other artificial features relative to the geographic pole shift over time; the Geographic South Pole is marked by a stake in the ice alongside a small sign.
The sign records the respective dates that Roald Amundsen and Robert F. Scott reached the Pole, followed by a short quotation from each man, gives the elevation as "9,301 FT.". A new marker stake is fabricated each year by staff at the site; the Ceremonial South Pole is an area set aside for photo opportunities at the South Pole Station. It is located some meters from the Geographic South Pole, consists of a metallic sphere on a short bamboo pole, surrounded by the flags of the original Antarctic Treaty signatory states. Amundsen's Tent: The tent was erected by the Norwegian expedition led by Roald Amundsen on its arrival on 14 December 1911, it is buried beneath the snow and ice in the vicinity of the Pole. It has been designated a Historic Site or Monument, following a proposal by Norway to the Antarctic Treaty Consultative Meeting; the precise location of the tent is unknown, but based on calculations of the rate of movement of the ice and the accumulation of snow, it is believed, as of 2010, to lie between 1.8 and 2.5 km from the Pole at a depth of 17 m below the present surface.
Argentine Flagpole: A flagpole erected at the South Geographical Pole in December 1965 by the First Argentine Overland Polar Expedition has been designated a Historic Site or Monument following a proposal by Argentina to the Antarctic Treaty Consultative Meeting. In 1820, several expeditions claimed to have been the first to have sighted Antarctica, with the first being the Russian expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev; the first landing was just over a year when American Captain John Davis, a sealer, set foot on the ice. The basic geography of the Antarctic coastline was not understood until the mid-to-late 19th century. American naval officer Charles Wilkes claimed that Antarctica was a new continent, basing the claim on his exploration in 1839–40, while James Clark Ross, in his expedition of 1839–43, hoped that he might be able to sail all the way to the South Pole. British explorer Robert Falcon Scott on the Discovery Expedition of 1901–04 was the first to attempt to find a route from the Antarctic coastline to the South Pole.
Scott, accompanied by Ernest Shackleton and Edward Wilson, set out with the aim of travelling as far south as possible, on 31 December 1902, reached 82°16′ S. Shackleton returned to Antarctica as leader of the British Antarctic Expedition in a bid to reach the Pole. On 9 January 1909, with three companions, he reached 88°23' S – 112 miles from the Pole – before being forced to turn back; the first men to reach the Geographic South Pole were the Norwegian Roald Amundsen and his party on December 14, 1911. Amundsen named his camp Polheim and the entire plateau surrounding the Pole King Haakon VII Vidde in honour of King Haakon VII of Norway. Robert Falcon Scott returned to Antarctica with his second expedition, the Terra Nova Expedition unaware of Amundsen's secretive expedition. Scott and four other men reached the South Pole on January 17, 1912, thirty-four days after Amundsen. On the return trip and his four companions all died of starvation and extreme cold. In 1914 Ernest Shackleton's Imperial Trans-Antarctic Expedition set out with the goal of crossing Antarctica via the South Pole, but his ship, the Endurance, was frozen in pack ice and sank 1
Canis Minor
Canis Minor is a small constellation in the northern celestial hemisphere. In the second century, it was included as an asterism, or pattern, of two stars in Ptolemy's 48 constellations, it is counted among the 88 modern constellations, its name is Latin for "lesser dog", in contrast to Canis Major, the "greater dog". Canis Minor contains only two stars brighter than the fourth magnitude, with a magnitude of 0.34, Gomeisa, with a magnitude of 2.9. The constellation's dimmer stars were noted by Johann Bayer, who named eight stars including Alpha and Beta, John Flamsteed, who numbered fourteen. Procyon is the seventh-brightest star in the night sky, as well as one of the closest. A yellow-white main sequence star, it has a white dwarf companion. Gomeisa is a blue-white main sequence star. Luyten's Star is a ninth-magnitude red dwarf and the Solar System's next closest stellar neighbour in the constellation after Procyon; the fourth-magnitude HD 66141, which has evolved into an orange giant towards the end of its life cycle, was discovered to have a planet in 2012.
There are two faint deep-sky objects within the constellation's borders. The 11 Canis-Minorids are a meteor shower. Though associated with the Classical Greek uranographic tradition, Canis Minor originates from ancient Mesopotamia. Procyon and Gomeisa were called MASH. TAB. BA or "twins" in the Three Stars Each tablets, dating to around 1100 BC. In the MUL. APIN, this name was applied to the pairs of Pi3 and Pi4 Orionis and Zeta and Xi Orionis; the meaning of MASH. TAB. BA evolved as well, becoming the twin deities Lulal and Latarak, who are on the opposite side of the sky from Papsukal, the True Shepherd of Heaven in Babylonian mythology. Canis Minor was given the name DAR. LUGAL, its position defined as "the star which stands behind it ", in the MUL. APIN; this name may have referred to the constellation Lepus. DAR. LUGAL was denoted DAR. MUŠEN and DAR. LUGAL. MUŠEN in Babylonia. Canis Minor was called tarlugallu in Akkadian astronomy. Canis Minor was one of the original 48 constellations formulated by Ptolemy in his second-century Almagest, in which it was defined as a specific pattern of stars.
The Ancient Greeks called the constellation προκυων/Procyon, "coming before the dog", transliterated into Latin as Antecanis, Praecanis, or variations thereof, by Cicero and others. Roman writers appended the descriptors parvus, minor or minusculus, primus or sinister to its name Canis. In Greek mythology, Canis Minor was sometimes connected with the Teumessian Fox, a beast turned into stone with its hunter, Laelaps, by Zeus, who placed them in heaven as Canis Major and Canis Minor. Eratosthenes accompanied the Little Dog with Orion, while Hyginus linked the constellation with Maera, a dog owned by Icarius of Athens. On discovering the latter's death, the dog and Icarius' daughter Erigone took their lives and all three were placed in the sky—Erigone as Virgo and Icarius as Boötes; as a reward for his faithfulness, the dog was placed along the "banks" of the Milky Way, which the ancients believed to be a heavenly river, where he would never suffer from thirst. The medieval Arabic astronomers maintained the depiction of Canis Minor as a dog.
There was one slight difference between the Ptolemaic vision of the Arabic. The Arabic names for both Procyon and Gomeisa alluded to their proximity and resemblance to Sirius, though they were not direct translations of the Greek. Among the Merazig of Tunisia, shepherds note six constellations that mark the passage of the dry, hot season. One of them, called Merzem, includes the stars of Canis Minor and Canis Major and is the herald of two weeks of hot weather; the ancient Egyptians thought of this constellation as the jackal god. Alternative names have been proposed: Johann Bayer in the early 17th century termed the constellation Fovea "The Pit", Morus "Sycamine Tree". Seventeenth-century German poet and author Philippus Caesius linked it to the dog of Tobias from the Apocrypha. Richard A. Proctor gave the constellation the name Felis "the Cat" in 1870, explaining that he sought to shorten the constellation names to make them more manageable on celestial charts. Canis Minor is confused with Canis Major and given the name Canis Orionis.
In Chinese astronomy, the stars corresponding to Canis Minor lie in the Vermilion Bird of the South. Procyon and Eta Canis Minoris form an asterism known as Nánhé, the Southern River. With its counterpart, the Northern River Beihe, Nánhé was associated with a gate or sentry. Along with Zeta and 8 Cancri, 6 Canis Minoris and 11 Canis Minoris formed the asterism Shuiwei, which means "water level". Combined with additional stars in Gemini, Shuiwei represented an official who managed floodwaters or a marker of the water level. Neighboring Kore
