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81-508: His Tractus Rectanguli , describing the rectangulus, was an influential text in medieval astronomy and at least thirty copies were known to survive. His Quadripartitum was the first text on spherical trigonometry to be published in Western Europe. The rectangulus was a form of skeleton torquetum . This was a series of nested angular scales, so that measurements in azimuth and elevation could be made directly in polar coordinates, relative to

162-422: A peanut , a potato , or an avocado . Its mass is roughly 2.2 × 10  kg, with an average density of about 0.55 grams per cubic centimetre (0.32 oz/cu in). The low density indicates that it is made of a large number of small pieces, held together very loosely, forming a structure known as a rubble pile . Ground-based observations of coma brightness suggested that Halley's rotation period

243-551: A spacecraft , Giotto , providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation. These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple 's "dirty snowball" model, which correctly predicted that Halley would be composed of a mixture of volatile ices —such as water , carbon dioxide , ammonia —and dust . The missions also provided data that substantially reformed and reconfigured these ideas; for instance, it

324-570: A "comet-star" appeared in the sky in the year 1067 (the chronicle is erroneous, as the event occurred in 1066, and by Robert he means William). The Emperor Constantine Ducas died in the month of May, and his son Michael received the Empire. And in this year there appeared a comet star, and the Norman count Robert [sic] fought a battle with Harold, King of the English, and Robert was victorious and became king over

405-406: A German farmer and amateur astronomer. It did not pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused a delay of 618 days. This effect was computed before its return (with a one-month error to 13 April) by a team of three French mathematicians, Alexis Clairaut , Joseph Lalande , and Nicole-Reine Lepaute . The confirmation of the comet's return

486-481: A Sanskrit poet and biographer to the Sultans of Kashmir. He read the apparition as a cometary portent of doom foreshadowing the imminent fall of Sultan Zayn al-Abidin (AD 1418/1420–1470). After witnessing a bright light in the sky which most historians have identified as Halley's Comet, Zara Yaqob , Emperor of Ethiopia from 1434 to 1468, founded the city of Debre Berhan (tr. City of Light) and made it his capital for

567-449: A circle and 1 being a parabolic trajectory ). The perihelion, the point in the comet's orbit when it is nearest the Sun, is 0.59  au (88 million  km ). This is between the orbits of Mercury and Venus . Its aphelion , or farthest distance from the Sun, is 35 au (5.2 billion km), roughly the orbital distance of Pluto . Unlike the overwhelming majority of objects in

648-451: A comet appeared suspended over Rome for several days portending the death of Marcus Vipsanius Agrippa in that year. Halley's appearance in 12 BC, only a few years distant from the conventionally assigned date of the birth of Jesus Christ , has led some theologians and astronomers to suggest that it might explain the biblical story of the Star of Bethlehem . There are other explanations for

729-450: A free-spinning disk (unnamed) that can be locked into place, and the tabula orbis signorum, directly hinged to it above. The angle between these two pieces is defined by the basilica, a solid stand piece, which is used to either set the draft angle at 0 degrees (Where the basilica is removed) or 23.5 degrees, representing the off-set of the axis of rotation of the Earth. Whether or not the basilica

810-444: A list of 24 comet observations, he calculated that the orbital elements of a second comet that had appeared in 1682 were nearly the same as those of two comets that had appeared in 1531 (observed by Petrus Apianus ) and 1607 (observed by Johannes Kepler ). Halley thus concluded that all three comets were, in fact, the same object returning about every 76 years, a period that has since been found to vary between 72 and 80 years. After

891-438: A member of a new population of small Solar System bodies that serves as the source of Halley-type comets. Halley has probably been in its current orbit for 16,000–200,000 years, although it is not possible to numerically integrate its orbit for more than a few tens of apparitions, and close approaches before 837 AD can only be verified from recorded observations. The non-gravitational effects can be crucial; as Halley approaches

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972-459: A number of linear scales hinged above it. Pinhole sights on the upper arm allowed it to be pointed accurately at the astronomical target. Plumb bob lines descended from the scales above and intersected with linear scales marked on the horizontal scales below. These allowed measures to be read, not as angles, but as trigonometric ratios. To celebrate the 600th anniversary of the Rectangulus in 1926

1053-470: A particular comet. The Florentine chronicler Giovanni Villani wrote that the comet left "great trails of fumes behind", and that it remained visible from September 1301 until January 1302. It was seen by the artist Giotto di Bondone , who represented the Star of Bethlehem as a fire-coloured comet in the Nativity section of his Arena Chapel cycle, completed in 1305. Giotto's depiction includes details of

1134-524: A passage in the Babylonian Talmud , tractate Horayot that refers to "a star which appears once in seventy years that makes the captains of the ships err". Others doubt this idea based on historical considerations about the exact timing of this alleged observation, and suggest it refers to other astronomical phenomena. Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration starting from accurate observations in

1215-539: A quarter of that of the Moon . Halley came within 0.10  au of Earth at that time. This appearance of the comet is also noted in the Anglo-Saxon Chronicle . Eilmer of Malmesbury may have seen Halley in 989 and 1066, as recorded by William of Malmesbury : Not long after, a comet, portending (they say) a change in governments, appeared, trailing its long flaming hair through the empty sky: concerning which there

1296-459: A replica was constructed. This is now in the History of Science Museum, Oxford . Torquetum The torquetum or turquet is a medieval astronomical instrument designed by persons unknown to take and convert measurements made in three sets of coordinates: horizon, equatorial, and ecliptic. It is characterised by R. P. Lorch as a combination of Ptolemy 's astrolabon ( Greek : aστpoλaẞov ) and

1377-494: A rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758. While he had personally observed the comet around perihelion in September 1682, Halley died in 1742 before he could observe its predicted return. Halley's prediction of the comet's return proved to be correct, although it was not seen until 25 December 1758, by Johann Georg Palitzsch ,

1458-415: A torquetum model for his own personal use in the observation of Halley's Comet in the 1500s. The best-documented account of the torquetum was done by Peter Apian in 1532. Peter Apian was a German humanist, specializing in astronomy, mathematics, and cartography. In his book Astronomicum Caesareum (1540), Apian gives a description of the torquetum near the end of the second part. He also details how

1539-415: Is a similarly shaped component, the tabula equinoctialis, which represents the latitude of the Earth. This piece can rotate up to 90 degrees, coinciding with the latitudinal lines of the Earth from the equator to the poles. This angle of rotation is created by the stylus, which is an arm mechanism that pins to the slotted holes, which are part of the tabula orizontis. The midframe of the torquetum consists of

1620-493: Is about 4%, meaning that it reflects only 4% of the sunlight hitting it – about what one would expect for coal. Thus, despite astronomers predicting that Halley would have an albedo of about 0.17 (roughly equivalent to bare soil), Halley's Comet is in fact pitch black. The "dirty ices" on the surface sublime at temperatures between 170 K (−103 °C) in sections of higher albedo to 220 K (−53 °C) at low albedo; Vega 1 found Halley's surface temperature to be in

1701-554: Is associated with two meteor showers : the Eta Aquariids in early May, and the Orionids in late October. Halley is classified as a periodic or short-period comet : one with an orbit lasting 200 years or less. This contrasts it with long-period comets, whose orbits last for thousands of years. Periodic comets have an average inclination to the ecliptic of only ten degrees, and an orbital period of just 6.5 years, so Halley's orbit

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1782-458: Is atypical. Most short-period comets (those with orbital periods shorter than 20 years and inclinations of 30 degrees or less) are called Jupiter-family comets. Those resembling Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets. As of 2024 , 105 Halley-type comets have been observed, compared with 816 identified Jupiter-family comets. The orbits of

1863-448: Is believed by some Sikh scholars to be a reference to Halley's appearance in 1531. Halley's periodic returns have been subject to scientific investigation since the 16th century. The three apparitions from 1531 to 1682 were noted by Edmond Halley, enabling him to predict it would return. One key breakthrough occurred when Halley talked with Newton about his ideas of the laws of motion. Newton also helped Halley get John Flamsteed's data on

1944-649: Is estimated to be about 10 million years. The dynamics of its orbit can be approximately described by a two-dimensional symplectic map , known as the Kepler map , a solution to the restricted three-body problem for highly eccentric orbits. Based on records from the 1910 apparition, David Hughes calculated in 1985 that Halley's nucleus has been reduced in mass by 80 to 90% over the last 2,000 to 3,000 revolutions, and that it will most likely disappear completely after another 2,300 perihelion passages. More recent work suggests that Halley will evaporate, or split in two, within

2025-449: Is far more active than the night side. Spacecraft observations showed that the gases ejected from the nucleus were 80% water vapour, 17% carbon monoxide and 3–4% carbon dioxide, with traces of hydrocarbons although more recent sources give a value of 10% for carbon monoxide and also include traces of methane and ammonia . The dust particles were found to be primarily a mixture of carbon–hydrogen–oxygen–nitrogen (CHON) compounds common in

2106-408: Is included depends on the point of measurement either below or above the tropical latitudinal lines. Inscribed on the tabula equinoctialis along, although separate from, the outer perimeter of the bottom disk is a 24-hour circle, which is used to measure the angle between the longitudinal line facing the poles, and the line to the object being measured. Lastly, the upper frame is made up of the crista,

2187-635: Is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy. Comet Halley is usually pronounced / ˈ h æ l i / , rhyming with valley , or sometimes / ˈ h eɪ l i / , rhyming with daily . As to the surname Halley, Colin Ronan , one of Edmond Halley's biographers, preferred / ˈ h ɔː l i / , rhyming with crawly . Spellings of Halley's name during his lifetime included Hailey , Haley , Hayley , Halley , Haly , Hawley , and Hawly , so its contemporary pronunciation

2268-408: Is similar in function, it has not been identified as a torquetum , but evidence suggests it inspired the torquetum. The earliest explicit accounts of the torquetum appear in the 13th century writings of Bernard of Verdun and Franco of Poland. Franco of Poland's work was published in 1284; however, Bernard of Verdun's work does not contain a date. Therefore, it is impossible to know which work

2349-514: Is the only known short-period comet that is consistently visible to the naked eye from Earth , appearing every 72–80 years, though with the majority of recorded apparations (25 of 30) occuring after 75-77 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley , it is also commonly called Comet Halley , or sometimes simply Halley . Halley's periodic returns to

2430-498: Is uncertain, but the version rhyming with valley seems to be preferred by current bearers of the surname. Halley was the first comet to be recognised as periodic. Until the Renaissance , the philosophical consensus on the nature of comets, promoted by Aristotle , was that they were disturbances in Earth's atmosphere. This idea was disproven in 1577 by Tycho Brahe , who used parallax measurements to show that comets must lie beyond

2511-508: The Kuiper belt , a flat disc of icy debris between 30 au (Neptune's orbit) and 50 au from the Sun (in the scattered disc ). Another point of origin for the Halley-type comets was proposed in 2008, when a trans-Neptunian object with a retrograde orbit similar to Halley's was discovered, 2008 KV 42 , whose orbit takes it from just outside that of Uranus to twice the distance of Pluto. It may be

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2592-494: The Moon . Many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System. In 1687, Sir Isaac Newton published his Philosophiæ Naturalis Principia Mathematica , in which he outlined his laws of gravity and motion. His work on comets was decidedly incomplete. Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were

2673-406: The ecliptic . Conversion from these coordinates though was difficult, involving what was the leading mathematics of the day. The rectangulus was an analogue computing device to simplify this: instead of measuring in angular measurements it could resolve the angles to Cartesian components directly. This then simplified the further calculations. The rectangulus was constructed as a brass pillar with

2754-435: The inner Solar System have been observed and recorded by astronomers around the world since at least 240 BC, but it was not until 1705 that the English astronomer Edmond Halley understood that these appearances were re-appearances of the same comet. As a result of this discovery, the comet is named after Halley. During its 1986 visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by

2835-523: The Halley-type comets suggest that they were originally long-period comets whose orbits were perturbed by the gravity of the giant planets and directed into the inner Solar System. If Halley was once a long-period comet, it is likely to have originated in the Oort cloud , a sphere of cometary bodies around 20,000–50,000 au from the Sun. Conversely the Jupiter-family comets are generally believed to originate in

2916-631: The Popes  [ la ] that, A hairy and fiery star having then made its appearance for several days, the mathematicians declared that there would follow grievous pestilence, dearth and some great calamity. Calixtus, to avert the wrath of God, ordered supplications that if evils were impending for the human race He would turn all upon the Turks, the enemies of the Christian name. He likewise ordered, to move God by continual entreaty, that notice should be given by

2997-481: The Solar System, Halley's orbit is retrograde ; it orbits the Sun in the opposite direction to the planets, or, clockwise from above the Sun's north pole. The orbit is inclined by 18° to the ecliptic , with much of it lying south of the ecliptic. This is usually represented as 162°, to account for Halley's retrograde orbit. The 1910 passage was at a relative velocity of 70.56 km/s (157,800 mph). Because its orbit comes close to Earth's in two places, Halley

3078-615: The Sun on August 6 in 87 BC" as the comet would have been a "most recordable event"; for ancient Armenians it could have heralded the New Era of the brilliant King of Kings. The apparition of 12 BC was recorded in the Book of Han by Chinese astronomers of the Han dynasty who tracked it from August through October. It passed within 0.16 au of Earth. According to the Roman historian Cassius Dio ,

3159-487: The Sun, it expels jets of sublimating gas from its surface, which knock it very slightly off its orbital path. These orbital changes cause delays in its perihelion passage of four days on average. In 1989, Boris Chirikov and Vitold Vecheslavov performed an analysis of 46 apparitions of Halley's Comet taken from historical records and computer simulations, which showed that its dynamics were chaotic and unpredictable on long timescales. Halley's projected dynamical lifetime

3240-727: The artist. Halley's 1378 appearance is recorded in the Annales Mediolanenses as well as in East Asian sources. In 1456, the year of Halley's next apparition, the Ottoman Empire invaded the Kingdom of Hungary , culminating in the siege of Belgrade in July of that year. In a papal bull , Pope Callixtus III ordered special prayers be said for the city's protection. In 1470, the humanist scholar Bartolomeo Platina wrote in his Lives of

3321-655: The bells to call the faithful at midday to aid by their prayers those engaged in battle with the Turk. Platina's account is not mentioned in official records. In the 18th century, a Frenchman further embellished the story, in anger at the Church, by claiming that the Pope had "excommunicated" the comet, though this story was most likely his own invention. Halley's apparition of 1456 was also witnessed in Kashmir and depicted in great detail by Śrīvara,

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3402-469: The celestial bodies as they travel through space. The zero point for ascension is set to the vernal equinox while the end measurement (decline) is the equator, this would put the North Pole at the 90 degree point. The third and most commonly seen configuration of the "torquetum" uses all its assets to make measurements. The upper portion is now set at an angle equal to the obliquity of the ecliptic, which allows

3483-561: The coma, a sweeping tail, and the central condensation. According to the art historian Roberta Olson , it is much more accurate than other contemporary descriptions, and was not equaled in painting until the 19th century. Olson's identification of Halley's Comet in Giotto's Adoration of the Magi is what inspired the European Space Agency to name their mission to the comet Giotto , after

3564-608: The comet was seen in England and thought to be an omen : later that year Harold II of England died at the Battle of Hastings and William the Conqueror claimed the throne. The comet is represented on the Bayeux Tapestry and described in the tituli as a star. Surviving accounts from the period describe it as appearing to be four times the size of Venus , and shining with a light equal to

3645-482: The conception of the torquetum , the device had been put through many of the following uses. The astronomer, Peter of Limoges , used this device for his observation of what is known today as Halley's Comet at the turn of the 14th century. In the early 1300s, John of Murs mentions the torquetum as his defence "of the reliability of observational astronomy", thus further solidifying its practicality and viability in ancient astronomy. Additionally, Johannes Schoner built

3726-420: The device is used. Apian explains that the torquetum was used for astronomical observations and how the description of the instrument was used as a basis for common astronomical instruments. He also notes the manufacturing process of the instrument and the use of the torquetum for astronomical measurements. The torquetum is a complex medieval analog computer that measures three sets of astronomical coordinates:

3807-473: The first evidence in support of Fred Whipple 's "dirty snowball" hypothesis for comet construction; Whipple postulated that comets are icy objects warmed by the Sun as they approach the inner Solar System, causing ices on their surfaces to sublime (change directly from a solid to a gas), and jets of volatile material to burst outward, creating the coma. Giotto showed that this model was broadly correct, though with modifications. Halley's albedo , for instance,

3888-628: The historical record is a description from 240 BC, in the Chinese chronicle Records of the Grand Historian or Shiji , which describes a comet that appeared in the east and moved north. The only surviving record of the 164 BC apparition is found on two fragmentary Babylonian tablets, which were rediscovered in August 1984 in the collection of the British Museum . The apparition of 87 BC

3969-474: The horizon, equatorial, and ecliptic. One of the defining attributes of the torquetum is its ability to interconvert between these three sets of coordinate dimensions without the use of calculations, as well as to demonstrate the relationship between the same coordinate sets. However, it is a device that requires a thorough understanding of the components and how they work together to make relative positional measurements of certain celestial objects. The anatomy of

4050-438: The inscriptions on the disk and half disk, which make up the top of this particular kind of torquetum. A 14th century instrument, the rectangulus , was invented by Richard of Wallingford . This carried out the same task as the torquetum, but was calibrated with linear scales, read by plumb lines. This simplified the spherical trigonometry by resolving the polar measurements directly into their Cartesian components. Following

4131-407: The instrument to give ecliptic coordinates. This measures the celestial bodies now on celestial latitude and longitude scales which allow for greater precision and accuracy in making measurements. These three differing configurations allowed for added convenience in taking readings and made once tedious and complicated measuring more streamlined and simple. Halley%27s Comet Halley's Comet

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4212-422: The last major component is the perpendicular, a free-hanging pendulum which measures the angle between the radial line of the Earth and the measured object using the semis. The base of the instrument represents the horizon and is built on a hinge and a part known as the stylus holds the instrument up to the viewer's complementary latitude. This represents the celestial equator and the angle varies depending on where

4293-415: The meridian of the celestial sphere, which has four quadrants inscribed along the edges, each starting at 0 degrees along the horizontal, and 90 degrees along the vertical. Adjacent, and locked with the crista at 23.5 degrees angle is the semis, which is a half-circle composed of two quadrants starting at 0 degrees along the vertical (relative to 23.5-degree placement) and 90 degrees at the horizontal. Finally,

4374-525: The next few tens of thousands of years, or will be ejected from the Solar System within a few hundred thousand years. The Giotto and Vega missions gave planetary scientists their first view of Halley's surface and structure. The nucleus is a conglomerate of ices and dust , often referred to as a "dirty snowball". Like all comets, as Halley nears the Sun, its volatile compounds (those with low boiling points, such as water , carbon monoxide , carbon dioxide and other ices) begin to sublimate from

4455-585: The outer Solar System, and silicates, such as are found in terrestrial rocks. The dust particles ranged in size down to the limits of detection (≈0.001 μm). The ratio of deuterium to hydrogen in the water released by Halley was initially thought to be similar to that found in Earth's ocean water, suggesting that Halley-type comets may have delivered water to Earth in the distant past. Subsequent observations showed Halley's deuterium ratio to be far higher than that found in Earth's oceans, making such comets unlikely sources for Earth's water. Giotto provided

4536-438: The people of the English. The 1145 apparition may have been recorded by the monk Eadwine . According to legend, Genghis Khan was inspired to turn his conquests toward Europe by the westward-seeming trajectory of the 1222 apparition. In Korea, the comet was reportedly visible during the daylight on 9 September 1222. The 1301 apparition was visually spectacular, and may be the first that resulted in convincing portraits of

4617-522: The phenomenon, such as planetary conjunctions , and there are also records of other comets that appeared closer to the date of Jesus's birth. If Yehoshua ben Hananiah 's reference to "a star which arises once in seventy years and misleads the sailors" refers to Halley's Comet, he can only have witnessed the 66 AD appearance. Another possible report comes from Jewish historian Josephus , who wrote that in 66 AD "The signs ... were so evident, and did so plainly foretell their future desolation ... there

4698-480: The plane astrolabe . In a sense, the torquetum is an analog computer . The origins of the torquetum are unclear. Its invention has been credited to multiple figures, including Jabir ibn Aflah , Bernard of Verdun and Franco of Poland. Jabir ibn Aflah of Al-Andalus in the early 12th century has been assumed by several historians to be the inventor of the torquetum , based on a similar instrument he described in his Islah Almajisti . However, while his device

4779-435: The range 300–400 K (27–127 °C). This suggested that only 10% of Halley's surface was active, and that large portions of it were coated in a layer of dark dust that retained heat. Together, these observations suggested that Halley was in fact predominantly composed of non- volatile materials, and thus more closely resembled a "snowy dirtball" than a "dirty snowball". The first certain appearance of Halley's Comet in

4860-544: The remainder of his reign. Petrus Apianus and Girolamo Fracastoro described the comet's visit in 1531, with the former even including graphics in his publication. Through his observations, Apianus was able to prove that a comet's tail always points away from the Sun. In the Sikh scriptures of the Guru Granth Sahib , the founder of the faith Guru Nanak makes reference to " a long star that has risen " at Ang 1110, and it

4941-491: The same comet before and after passing behind the Sun (he was later found to be correct; see Newton's Comet ), he was initially unable to completely reconcile comets into his model. Ultimately, it was Newton's friend, editor and publisher, Edmond Halley , who, in his 1705 Synopsis of the Astronomy of Comets , used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits. Having compiled

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5022-428: The semis and the perpendiculum. The base of the crista is joined to another free-spinning disk directly above the tabula orbis signorum. Similarly, on the outer edge of the tabula orbis signorum is a zodiacal calendar and degree scale, with each of the 12 signs divided amongst it. This scale measures the zodiacal sector of the sky the object being measured is in. The crista itself is a circular piece that corresponds with

5103-467: The seventeenth and eighteenth centuries could not produce accurate results further back than 837 owing to a close approach to Earth in that year. It was necessary to use ancient Chinese comet observations to constrain their calculations. Halley's orbital period has varied between 74 and 80 years since 240 BC. Its orbit around the Sun is highly elliptical , with an orbital eccentricity of 0.967 (with 0 being

5184-561: The seventh of the Calends of May, on Tuesday after Little Easter, than whose light the brilliance or light of The Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards." Chaco Native Americans in New Mexico may have recorded the 1066 apparition in their petroglyphs. The Italo-Byzantine chronicle of Lupus the Protospatharios mentions that

5265-682: The sky. It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire, and the Middle East; Emperor Louis the Pious observed this appearance and devoted himself to prayer and penance, fearing that "by this token a change in the realm and the death of a prince are made known". In 912 AD, Halley is recorded in the Annals of Ulster , which states "A dark and rainy year. A comet appeared." In 1066,

5346-402: The solar light. Both processes are responsible for making the coma visible. As a fraction of the gas molecules in the coma are ionised by the solar ultraviolet radiation , pressure from the solar wind , a stream of charged particles emitted by the Sun, pulls the coma's ions out into a long tail , which may extend more than 100 million kilometres into space. Changes in the flow of

5427-558: The solar wind can cause disconnection events , in which the tail completely breaks off from the nucleus. Despite the vast size of its coma, Halley's nucleus is relatively small: barely 15 kilometres (9.3 mi) long, 8 kilometres (5.0 mi) wide and perhaps 8 kilometres (5.0 mi) thick. Based on a reanalysis of images taken by the Giotto and Vega spacecraft, Lamy et al. determined an effective diameter of 11 kilometres (6.8 mi). Its shape has been variously compared to that of

5508-416: The surface. This causes the comet to develop a coma , or atmosphere, at distances up to 230,000 kilometres (140,000 mi) from the nucleus. Sublimation of this dirty ice releases dust particles, which travel with the gas away from the nucleus. Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths, a phenomenon known as fluorescence , whereas dust particles scatter

5589-501: The target celestial body as well as use the base as a compass for viewing the possible paths they travel. The second configuration uses the stylus to elevate the base set at co-latitude of 90 degrees. The position of the celestial bodies can now be measured in hours, minutes, and seconds using the inscribed clock on the almuri. This helps give the proper ascension and decline coordinates of the celestial bodies as they travel through space. The zero point for ascension and decline coordinates of

5670-445: The tedious calculations required in previous instruments. The versatility of the "torquetum" can be seen in its three possible configurations for the measuring. The first method used lays the instruments flat on a table with no angles within the instrument set. This configuration gives the coordinates of celestial bodies as related to the horizon. The basilica is set so that 0 degree mark faces north. The user can now measure altitude of

5751-411: The torquetum involves many different components, which can be grouped into subdivisions of the torquetum structure, those being: the base, the midframe, and the upperframe. The base starts with the tabula orizontis, which is the bottommost rectangular piece in contact with the ground, and this component represents the horizon of the Earth, relative to the point of measurement. Hinged to the tabula orizontis

5832-399: The view is located on Earth. The several plates and circles that make up the upper portion of the instrument represent the celestial sphere. These parts are built on top of the base and above the basilica, which rotates on a pin to represent the axis of the Earth. The zodiac calendar is inscribed on the tabula orbis signorum this is part of the mechanical aspects of the instrument that take away

5913-481: Was a fine saying of a monk of our monastery called Æthelmær. Crouching in terror at the sight of the gleaming star, "You've come, have you?", he said. "You've come, you source of tears to many mothers. It is long since I saw you; but as I see you now you are much more terrible, for I see you brandishing the downfall of my country." The Irish Annals of the Four Masters recorded the comet as "A star [that] appeared on

5994-508: Was a star resembling a sword, which stood over the city, and a comet, that continued a whole year". This portent was in reference to the city of Jerusalem and the First Jewish–Roman War . The 141 AD apparition was recorded in Chinese chronicles, with observations of a bluish white comet on 27 March and 16, 22 and 23 April. The 374 AD and 607 approaches each came within 0.09  au of Earth. The 451 AD apparition

6075-451: Was about 7.4 days. Images taken by the various spacecraft, along with observations of the jets and shell, suggested a period of 52 hours. Given the irregular shape of the nucleus, Halley's rotation is likely to be complex. The flyby images revealed an extremely varied topography, with hills, mountains, ridges, depressions, and at least one crater. Halley's day side (the side facing the Sun)

6156-461: Was by instrument-maker, Erasmus Habermel. His alteration allowed for astronomers to make observations to all three of the scales. A torquetum can be seen in the famous portrait The Ambassadors (1533) by Hans Holbein the Younger . It is placed on the right side of the table, next to and above the elbow of the ambassador clad in a long brown coat or robe. The painting shows much of the details of

6237-597: Was recorded in Babylonian tablets which state that the comet was seen "day beyond day" for a month. This appearance may be recalled in the representation of Tigranes the Great , an Armenian king who is depicted on coins with a crown that features, according to Vahe Gurzadyan and R. Vardanyan, "a star with a curved tail [that] may represent the passage of Halley's Comet in 87 BC." Gurzadyan and Vardanyan argue that "Tigranes could have seen Halley's Comet when it passed closest to

6318-504: Was said to herald the defeat of Attila the Hun at the Battle of Chalons . The 684 AD apparition was reported in Chinese records as the "broom star". The 760 AD apparition was recorded in the Zuqnin Chronicle ' s entry for iyyōr 1071 SE (May 760 AD ), calling it a "white sign": The year [SE] one thousand seventy one (AD 759/760). In the month of iyyōr (May) a white sign

6399-599: Was seen in the sky, before early twilight, in the north-east [quarter], in the Zodiac [sign] which is called Aries, to the north from these three stars in it, which are very shining. And it resembled in its shape a broom [...] And the sign itself remained for fifteen nights, until dawn of the feast of Pentecost . In 837 AD, Halley's Comet may have passed as close as 0.03 astronomical units (2.8 million miles; 4.5 million kilometres) from Earth , by far its closest approach. Its tail may have stretched 60  degrees across

6480-505: Was the first time anything other than planets had been shown to orbit the Sun. It was also one of the earliest successful tests of Newtonian physics , and a clear demonstration of its explanatory power. The comet was first named in Halley's honour by French astronomer Nicolas-Louis de Lacaille in 1759. Some scholars have proposed that first-century Mesopotamian astronomers already had recognised Halley's Comet as periodic. This theory notes

6561-426: Was written first. Franco's work was more widely known and is credited with the distribution of knowledge about the torquetum . The instrument was first created sometime in the 12th or 13th century. However, the only surviving examples of the torquetum are dated from the 16th century. In the middle of the 16th century, the torquetum had numerous structural changes to the original design. The most important change

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