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112-493: A sunbeam , in meteorological optics , is a beam of sunlight that appears to radiate from the position of the Sun . Shining through openings in clouds or between other objects such as mountains and buildings, these beams of particle-scattered sunlight are essentially parallel shafts separated by darker shadowed volumes. Their apparent convergence in the sky is a visual illusion from linear perspective . The same illusion causes

224-479: A baronial council and more frequent parliaments . Pope Urban IV absolved the king of his oath in 1261 and, after initial abortive resistance , Simon de Montfort led a force, enlarged due to recent crop failures, that prosecuted the Second Barons' War . Bacon's own family were considered royal partisans: De Montfort's men seized their property and drove several members into exile. In 1256 or 1257, he became

336-529: A friar in the Franciscan Order in either Paris or Oxford, following the example of scholarly English Franciscans such as Grosseteste and Marsh . After 1260, Bacon's activities were restricted by a statute prohibiting the friars of his order from publishing books or pamphlets without prior approval. He was likely kept at constant menial tasks to limit his time for contemplation and came to view his treatment as an enforced absence from scholarly life. By

448-629: A philosophy of science that would guide the others. The section on geography was allegedly originally ornamented with a map based on ancient and Arabic computations of longitude and latitude, but has since been lost. His (mistaken) arguments supporting the idea that dry land formed the larger proportion of the globe were apparently similar to those which later guided Columbus . In this work Bacon criticises his contemporaries Alexander of Hales and Albertus Magnus , who were held in high repute despite having only acquired their knowledge of Aristotle at second hand during their preaching careers. Albert

560-476: A collection of definitive texts on these subjects. The new subjects were to be "perspective" (i.e., optics ), "astronomy" (inclusive of astronomy proper, astrology , and the geography necessary to use them), "weights" (likely some treatment of mechanics but this section of the Opus Majus has been lost), alchemy , agriculture (inclusive of botany and zoology ), medicine , and " experimental science",

672-417: A demon but causes the head to speak by "the continuall fume of the six hottest Simples", testing his theory that speech is caused by "an effusion of vapors". Around 1589, Robert Greene adapted the story for the stage as The Honorable Historie of Frier Bacon and Frier Bongay , one of the most successful Elizabethan comedies . As late as the 1640s, Thomas Browne was still complaining that "Every ear

784-578: A gun barrel. The ~41% nitrate content is too low to have explosive properties. Bacon attributed the Secret of Secrets ( Secretum Secretorum ), the Islamic "Mirror of Princes" ( Arabic : Sirr al-ʿasrar ), to Aristotle , thinking that he had composed it for Alexander the Great . Bacon produced an edition of Philip of Tripoli 's Latin translation, complete with his own introduction and notes; and his writings of

896-490: A likely-forged letter to an unknown "William of Paris," dismisses practices such as necromancy but contains most of the alchemical formulae attributed to Bacon, including one for a philosopher's stone and another possibly for gunpowder . It also includes several passages about hypothetical flying machines and submarines , attributing their first use to Alexander the Great . On the Vanity of Magic or The Nullity of Magic

1008-470: A noise] exceeding the roar of strong thunder, and a flash brighter than the most brilliant lightning. At the beginning of the 20th century, Henry William Lovett Hime of the Royal Artillery published the theory that Bacon's Epistola contained a cryptogram giving a recipe for the gunpowder he witnessed. The theory was criticised by Thorndike in a 1915 letter to Science and several books,

1120-441: A percentage of the light which enters the cloud is not reflected back out before it is absorbed. A simple example of this is being able to see farther in heavy rain than in heavy fog. This process of reflection / absorption is what causes the range of cloud color from white to black. Other colors occur naturally in clouds. Bluish-grey is the result of light scattering within the cloud. In the visible spectrum, blue and green are at

1232-420: A position joined by Muir , John Maxson Stillman , Steele , and Sarton . Needham et al. concurred with these earlier critics that the additional passage did not originate with Bacon and further showed that the proportions supposedly deciphered (a 7:5:5 ratio of saltpetre to charcoal to sulphur ) as not even useful for firecrackers, burning slowly with a great deal of smoke and failing to ignite inside

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1344-521: A real optical phenomenon which can be captured on camera, since light rays actually are refracted to form the false image at the observer's location. What the image appears to represent, however, is determined by the interpretive faculties of the human mind. For example, inferior images on land are very easily mistaken for the reflections from a small body of water. Mirages can be categorized as "inferior" (meaning lower), "superior" (meaning higher) and " Fata Morgana ", one kind of superior mirage consisting of

1456-674: A revision of the medieval university curriculum, which saw the addition of optics to the traditional quadrivium . Bacon's major work, the Opus Majus , was sent to Pope Clement IV in Rome in 1267 upon the pope's request. Although gunpowder was first invented and described in China , Bacon was the first in Europe to record its formula. Roger Bacon was born in Ilchester in Somerset , England , in

1568-541: A series of both inverted and erect images. A Fata Morgana is an unusual and very complex form of mirage, a form of superior mirage , which, like many other kinds of superior mirages, is seen in a narrow band right above the horizon. It is an Italian phrase derived from the vulgar Latin for "fairy" and the Arthurian sorcerer Morgan le Fay , from a belief that the mirage, often seen in the Strait of Messina , were fairy castles in

1680-602: A series of unusually elaborate, vertically stacked images, which form one rapidly changing mirage. Green flashes and green rays are optical phenomena that occur shortly after sunset or before sunrise, when a green spot is visible, usually for no more than a second or two, above the Sun, or a green ray shoots up from the sunset point. Green flashes are actually a group of phenomena stemming from different causes, and some are more common than others. Green flashes can be observed from any altitude (even from an aircraft). They are usually seen at an unobstructed horizon , such as over

1792-726: A summary of the sciences. In fact, he had no money to research, let alone copy, such a work and attempts to secure financing from his family were thwarted by the Second Barons' War. However, in 1265, Guy was summoned to a conclave at Perugia that elected him Pope Clement IV . William Benecor, who had previously been the courier between Henry III and the pope, now carried the correspondence between Bacon and Clement. Clement's reply of 22 June 1266 commissioned "writings and remedies for current conditions", instructing Bacon not to violate any standing "prohibitions" of his order but to carry out his task in utmost secrecy. While faculties of

1904-405: A tropospheric cloud matures, the dense water droplets may combine to produce larger droplets, which may combine to form droplets large enough to fall as rain. By this process of accumulation, the space between droplets becomes increasingly larger, permitting light to penetrate farther into the cloud. If the cloud is sufficiently large and the droplets within are spaced far enough apart, it may be that

2016-400: A year. Pope Clement died in 1268 and Bacon lost his protector. The Condemnations of 1277 banned the teaching of certain philosophical doctrines, including deterministic astrology. Some time within the next two years, Bacon was apparently imprisoned or placed under house arrest . This was traditionally ascribed to Franciscan Minister General Jerome of Ascoli , probably acting on behalf of

2128-458: Is a debunking of esoteric claims in Bacon's time, showing that they could be explained by natural phenomena. He wrote on the medicine of Galen , referring to the translations of Avicenna . He believed that the medicine of Galen belonged to an ancient tradition passed through Chaldeans , Greeks and Arabs . Although he provided a negative image of Hermes Trismegistus , his work was influenced by

2240-549: Is a polar mirage caused by high refraction of sunlight between atmospheric thermoclines . The Novaya Zemlya effect will give the impression that the sun is rising earlier or setting later than it actually should (astronomically speaking). Depending on the meteorological situation the effect will present the Sun as a line or a square (which is sometimes referred to as the "rectangular sun"), made up of flattened hourglass shapes. The mirage requires rays of sunlight to have an inversion layer for hundreds of kilometres, and depends on

2352-543: Is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage , from the Latin mirare , meaning "to look at, to wonder at". This is the same root as for "mirror" and "to admire". Also, it has its roots in the Arabic mirage . In contrast to a hallucination , a mirage is

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2464-490: Is also evident through his citations of classic Hermetic literature such as the Corpus Hermeticum. Bacon's citation of the Corpus Hermeticum, which consists of a dialogue between Hermes and the pagan deity Asclepius , proves that Bacon's ideas were much more in line with the spiritual aspects of alchemy rather than the scientific aspects. However, this is somewhat paradoxical as what Bacon was specifically trying to prove in

2576-419: Is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air. This temperature inversion is the opposite of what is normally the case; air is usually warmer close to the surface, and cooler higher up. In calm weather, a layer of significantly warmer air can rest over colder dense air, forming an atmospheric duct which acts like a refracting lens , producing

2688-488: Is due to two internal reflections within a drop. The resulting secondary arc is some 3° wide and the colours are reversed, with blue/violet on the outside. Two internal reflections produce a bow with angular size of 50.5° to 54° with blue/violet on the outside. The region between a double rainbow is often noticeably darker that the sky withinthe primary bow and that beyond the seconday bow. It known an Alexander's Dark Band. The reason for this apparent reduction in sky brightness

2800-453: Is filled with the story of Frier Bacon, that made a brazen head to speak these words, Time is ". Greene's Bacon spent seven years creating a brass head that would speak "strange and uncouth aphorisms" to enable him to encircle Britain with a wall of brass that would make it impossible to conquer. Unlike his source material, Greene does not cause his head to operate by natural forces but by " nigromantic charms" and "the enchanting forces of

2912-399: Is going on inside the cloud. Dense deep tropospheric clouds exhibit a high reflectance (70% to 95%) throughout the visible spectrum . Tiny particles of water are densely packed and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color, especially when viewed from the top. Cloud droplets tend to scatter light efficiently, so that

3024-464: Is greater in the forward and backward directions than it is in the lateral direction. Individual water droplets exposed to white light will create a set of colored rings. If a cloud is thick enough, scattering from multiple water droplets will wash out the set of colored rings and create a washed out white color. Dust from the Sahara moves around the southern periphery of the subtropical ridge moves into

3136-507: Is less interested in a full practical mastery of the other languages than on a theoretical understanding of their grammatical rules, ensuring that a Latin reader will not misunderstand passages' original meaning . For this reason, his treatments of Greek and Hebrew grammar are not isolated works on their topic but contrastive grammars treating the aspects which influenced Latin or which were required for properly understanding Latin texts. He pointedly states, "I want to describe Greek grammar for

3248-484: Is most obvious. Crepuscular comes from the Latin word "crepusculum", meaning twilight. Crepuscular rays usually appear orange because the path through the atmosphere at sunrise and sunset passes through up to 40 times as much air as rays from a high midday sun. Particles in the air scatter short wavelength light (blue and green) through Rayleigh scattering much more strongly than longer wavelength yellow and red light. Loosely,

3360-425: Is much like if a person were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads this can produce blood-red clouds. Clouds look darker in the near- infrared because water absorbs solar radiation at those wavelengths . A halo (ἅλως; also known as a nimbus, icebow or gloriole) is an optical phenomenon produced by the interaction of light from the Sun or Moon with ice crystals in

3472-511: Is much smaller than a rainbow, ranging between 5° and 20°, depending on the size of the droplets. The glory can only be seen when the observer is directly between the Sun and cloud of refracting water droplets. Hence, it is commonly observed while airborne, with the glory surrounding the airplane's shadow on clouds (this is often called The Glory of the Pilot ). Glories can also be seen from mountains and tall buildings, when there are clouds or fog below

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3584-482: Is no evidence he was ever awarded a doctorate. (The title Doctor Mirabilis was a posthumous scholastic accolade .) A caustic cleric named Roger Bacon is recorded speaking before the king at Oxford in 1233. In 1237 or at some point in the following decade, he accepted an invitation to teach at the University of Paris . While there, he lectured on Latin grammar , Aristotelian logic , arithmetic , geometry , and

3696-402: Is one and the same in all languages, substantially, though it may vary, accidentally, in each of them. However, Bacon's lack of interest in studying a literal grammar underlying the languages known to him and his numerous works on linguistics and comparative linguistics has prompted Hovdhaugen to question the usual literal translation of Bacon's grammatica in such passages. She notes

3808-501: Is still unknown, but it could be due to the combination of reddened sunlight passing through very optically thick clouds. Yellowish clouds may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. Yellowish clouds caused by the presence of nitrogen dioxide are sometimes seen in urban areas with high air pollution levels. Red, orange and pink clouds occur almost entirely at sunrise and sunset and are

3920-420: Is that, while light from the sky enclosed within the primary bow comes from droplet reflection, and light beyond the secondary bow also comes from droplet reflection, there is no mechanism for the region between the bows to reflect light in the direction of the observer. Generally speaking, larger the droplets make for brighter bows. A rainbow spans a continuous spectrum of colors; the distinct bands (including

4032-435: Is the glory. A glory is an optical phenomenon, appearing much like an iconic Saint 's halo about the head of the observer, produced by light backscattered (a combination of diffraction , reflection and refraction ) towards its source by a cloud of uniformly sized water droplets. A glory has multiple colored rings, with red colors on the outermost ring and blue/violet colors on the innermost ring. The angular distance

4144-488: The Summulae Dialectices or Summulae super Totam Logicam . These are mature but essentially conventional presentations of Oxford and Paris's terminist and pre- modist logic and grammar. His later work in linguistics is much more idiosyncratic, using terminology and addressing questions unique in his era. In his Greek and Hebrew Grammars ( Grammatica Graeca and Hebraica ), in his work "On

4256-752: The Renaissance Hermetic thought . Bacon's endorsement of Hermetic philosophy is evident, as his citations of the alchemical literature known as the Secretum Secretorum made several appearances in the Opus Majus. The Secretum Secretorum contains knowledge about the Hermetic Emerald Tablet , which was an integral component of alchemy, thus proving that Bacon's version of alchemy was much less secular, and much more spiritual than once interpreted. The importance of Hermetic philosophy in Bacon's work

4368-493: The devil ": i.e., by entrapping a dead spirit or hobgoblin . Bacon collapses, exhausted, just before his device comes to life and announces "Time is", "Time was", and "Time is Past" before being destroyed in spectacular fashion: the stage direction instructs that " a lightening flasheth forth, and a hand appears that breaketh down the Head with a hammer ". A necromantic head was ascribed to Pope Sylvester II as early as

4480-505: The early modern period , the English considered him the epitome of a wise and subtle possessor of forbidden knowledge , a Faust -like magician who had tricked the devil and so was able to go to heaven . Of these legends, one of the most prominent was that he created a talking brazen head which could answer any question. The story appears in the anonymous 16th-century account of The Famous Historie of Fryer Bacon , in which Bacon speaks with

4592-403: The scholastic accolade Doctor Mirabilis , was a polymath , a medieval English philosopher , scientist , theologian and Franciscan friar who placed considerable emphasis on the study of nature through empiricism . Intertwining his Catholic faith with scientific thinking, Roger Bacon is considered one of the greatest polymaths of the medieval period . In the early modern era , he

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4704-493: The trivium or quadrivium that formed the medieval curriculum . His family appears to have been well off. Bacon studied at Oxford . While Robert Grosseteste had probably left shortly before Bacon's arrival, his work and legacy almost certainly influenced the young scholar and it is possible Bacon subsequently visited him and William of Sherwood in Lincoln . Bacon became a Master at Oxford, lecturing on Aristotle . There

4816-411: The twilight period). This apparent dual convergence (at both the solar and the antisolar points) is a perspective effect analogous to the apparent dual convergence of the parallel lines of a long straight road or hallway at directly opposite points (to an observer above the ground). Meteorological optics Meteorological optical phenomena, as described in this article, are concerned with how

4928-458: The "Compendium of the Study of Philosophy" and "of Theology" ( Compendium Studii Philosophiae and Theologiae ), and his Computus . The "Compendium of the Study of Theology", presumably written in the last years of his life, was an anticlimax: adding nothing new, it is principally devoted to the concerns of the 1260s. The Mirror of Alchimy ( Speculum Alchemiae ), a short treatise on

5040-406: The "sentence method" then fashionable. Bacon also sent his Opus Minus , De Multiplicatione Specierum , De Speculis Comburentibus , an optical lens, and possibly other works on alchemy and astrology . The entire process has been called "one of the most remarkable single efforts of literary productivity", with Bacon composing referenced works of around a million words in about

5152-576: The 1120s, but Browne considered the legend to be a misunderstanding of a passage in Peter the Good 's c.  1335 Precious Pearl where the negligent alchemist misses the birth of his creation and loses it forever. The story may also preserve the work by Bacon and his contemporaries to construct clockwork armillary spheres . Bacon had praised a "self-activated working model of the heavens" as "the greatest of all things which have been devised". As early as

5264-459: The 1260s and 1270s cite it far more than his contemporaries did. This led Easton and others, including Robert Steele , to argue that the text spurred Bacon's own transformation into an experimentalist. (Bacon never described such a decisive impact himself.) The dating of Bacon's edition of the Secret of Secrets is a key piece of evidence in the debate, with those arguing for a greater impact giving it an earlier date; but it certainly influenced

5376-407: The 16th century, natural philosophers such as Bruno , Dee and Francis Bacon were attempting to rehabilitate Bacon's reputation and to portray him as a scientific pioneer who had avoided the petty bickering of his contemporaries to attempt a rational understanding of nature. By the 19th century, commenters following Whewell considered that "Bacon ... was not appreciated in his age because he

5488-743: The Franciscans", interest in certain astrological doctrines, or generally combative personality rather than from "any scientific novelties which he may have proposed". Sometime after 1278, Bacon returned to the Franciscan House at Oxford, where he continued his studies and is presumed to have spent most of the remainder of his life. His last dateable writing—the Compendium Studii Theologiae —was completed in 1292. He seems to have died shortly afterwards and been buried at Oxford. Medieval European philosophy often relied on appeals to

5600-603: The Moon illusion gradually came to be accepted as a psychological phenomenon, with Ptolemy's theory being rejected in the 17th century. For over 100 years, research on the Moon illusion has been conducted by vision scientists who invariably have been psychologists specializing in human perception . After reviewing the many different explanations in their 2002 book The Mystery of the Moon Illusion , Ross and Plug concluded "No single theory has emerged victorious". The color of light from

5712-504: The Opus Majus and subsequent works, was that spirituality and science were the same entity. Bacon believed that by using science, certain aspects of spirituality such as the attainment of "Sapientia" or "Divine Wisdom" could be logically explained using tangible evidence. Bacon's Opus Majus was first and foremost, a compendium of sciences which he believed would facilitate the first step towards "Sapientia". Bacon placed considerable emphasis on alchemy and even went so far as to state that alchemy

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5824-509: The Science of Perspective " ( De Scientia Perspectivae ), "On Experimental Knowledge" ( De Scientia Experimentali ), and "A Philosophy of Morality" ( Moralis Philosophia ). It was not intended as a complete work but as a "persuasive preamble" ( persuasio praeambula ), an enormous proposal for a reform of the medieval university curriculum and the establishment of a kind of library or encyclopedia, bringing in experts to compose

5936-477: The Sun and Moon larger at the horizon than when they are higher in the sky, he redefined the problem in terms of perceived, rather than real, enlargement. He said that judging the distance of an object depends on there being an uninterrupted sequence of intervening bodies between the object and the observer. Critically, Ibn al-Haytham said that judging the size of an object depends on its judged distance: an object that appears near appears smaller than an object having

6048-431: The Sun. For an observer on the ground, the amount of the arc that is visible depends on the height of the sun above the horizon. It is a full semicircle with an angular radius of 42° when the sun is at the horizon. But as the sun rises in the sky, the arc grows smaller and ceases to be visible when the sun is more than 42° above the horizon. To see more than a semicircular bow, an observer would have to be able to look down on

6160-562: The Usefulness of Grammar" (Book III of the Opus Majus ), and in his Compendium of the Study of Philosophy , Bacon stresses the need for scholars to know several languages. Europe's vernacular languages are not ignored—he considers them useful for practical purposes such as trade , proselytism , and administration —but Bacon is mostly interested in his era's languages of science and religion: Arabic , Greek , Hebrew and Latin . Bacon

6272-420: The air, or false land designed to lure sailors to their death created by her witchcraft. Although the term Fata Morgana is sometimes incorrectly applied to other, more common kinds of mirages, the true Fata Morgana is not the same as an ordinary superior mirage, and is certainly not the same as an inferior mirage . Fata Morgana mirages tremendously distort the object or objects which they are based on, such that

6384-451: The ambiguity in the Latin term, which could refer variously to the structure of language, to its description, and to the science underlying such descriptions: i.e., linguistics . Bacon states that his Lesser Work ( Opus Minus ) and Third Work ( Opus Tertium ) were originally intended as summaries of the Opus Majus in case it was lost in transit. Easton 's review of the texts suggests that they became separate works over

6496-404: The apparent convergence of parallel lines on a long straight road or hallway at a distant vanishing point . The scattering particles that make sunlight visible may be air molecules or particulates . Crepuscular rays or god rays are sunbeams that originate when the sun is just below the horizon, during twilight hours. Crepuscular rays are noticeable when the contrast between light and dark

6608-455: The atmosphere, resulting in colored or white arcs, rings or spots in the sky. Many halos are positioned near the Sun or Moon, but others are elsewhere and even in the opposite part of the sky. They can also form around artificial lights in very cold weather when ice crystals called diamond dust are floating in the nearby air. There are many types of ice halos. They are produced by the ice crystals in cirrus or cirrostratus clouds high in

6720-492: The authority of Church Fathers such as St Augustine , and on works by Plato and Aristotle only known at second hand or through Latin translations. By the 13th century, new works and better versions – in Arabic or in new Latin translations from the Arabic – began to trickle north from Muslim Spain . In Roger Bacon's writings, he upholds Aristotle's calls for the collection of facts before deducing scientific truths, against

6832-512: The benefit of Latin speakers". It is likely only this limited sense which was intended by Bacon's boast that he could teach an interested pupil a new language within three days. Passages in the Overview and the Greek grammar have been taken as an early exposition of a universal grammar underlying all human languages . The Greek grammar contains the tersest and most famous exposition: Grammar

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6944-531: The course of the laborious process of creating a fair copy of the Opus Majus , whose half-million words were copied by hand and apparently greatly revised at least once. Other works by Bacon include his "Tract on the Multiplication of Species" ( Tractatus de Multiplicatione Specierum ), "On Burning Lenses" ( De Speculis Comburentibus ), the Communia Naturalium and Mathematica ,

7056-410: The crystals are increasingly skewed from the horizontal plane. Their angle of deviation increases and the sundogs move further from the Sun. However, they always stay at the same elevation as the Sun. Sun dogs are red-colored at the side nearest the Sun. Farther out the colors grade to blue or violet. However, the colors overlap considerably and so are muted, rarely pure or saturated. The colors of

7168-408: The direction opposite the sun. They appear to converge again at the distant horizon. Atmospheric refraction influences the apparent position of astronomical and terrestrial objects, usually causing them to appear higher than they actually are. For this reason navigators, astronomers, and surveyors observe positions when these effects are minimal. Sailors will only shoot a star when 20° or more above

7280-412: The drops, say from an airplane or a mountaintop. Rainbows are most common during afternoon rain showers in summer. A single reflection off the backs of an array of raindrops produces a rainbow with an angular size that ranges from 40° to 42° with red on the outside and blue/violet on the inside. This is known as the primary bow. A fainter secondary bow is often visible some 10° outside the primary bow. It

7392-537: The early 13th century. His birth is sometimes narrowed down to 1210, 1213 or 1214, 1215 or 1220. The only source for his birth date is a statement from his 1267 Opus Tertium that "forty years have passed since I first learned the Alphabetum ". The latest dates assume this referred to the alphabet itself, but elsewhere in the Opus Tertium it is clear that Bacon uses the term to refer to rudimentary studies,

7504-535: The elder Bacon's conception of the political aspects of his work in the sciences. Bacon has been credited with a number of alchemical texts. The Letter on the Secret Workings of Art and Nature and on the Vanity of Magic ( Epistola de Secretis Operibus Artis et Naturae et de Nullitate Magiae ), also known as On the Wonderful Powers of Art and Nature ( De Mirabili Potestate Artis et Naturae ),

7616-508: The first European descriptions of a mixture containing the essential ingredients of gunpowder . Partington and others have come to the conclusion that Bacon most likely witnessed at least one demonstration of Chinese firecrackers , possibly obtained by Franciscans—including Bacon's friend William of Rubruck —who visited the Mongol Empire during this period. The most telling passage reads: We have an example of these things (that act on

7728-543: The horizon, astronomers try to schedule observations when an object is highest in the sky, and surveyors try to observe in the afternoon when refraction is minimum. Atmospheric diffraction is a visual effect caused when sunlight is bent by particles suspended in the air. Atmospheric optical phenomena include: Roger Bacon Roger Bacon OFM ( / ˈ b eɪ k ən / ; Latin : Rogerus or Rogerius Baconus, Baconis , also Frater Rogerus ; c.  1219/20  – c.  1292 ), also known by

7840-403: The ice. Also they are also viewed in days when the sun hits the clouds in a perfect angle shining upon the area. There are three primary forms of crepuscular rays : They are commonly seen near sunrise and sunset, when tall clouds such as cumulonimbus and mountains can be most effective at creating these rays. Anticrepuscular rays while parallel in reality are sometimes visible in the sky in

7952-428: The integration of philosophy from apostate philosopher of the Islamic world into Christian learning. In Part IV of the Opus Majus , Bacon proposed a calendrical reform similar to the later system introduced in 1582 under Pope Gregory XIII . Drawing on ancient Greek and medieval Islamic astronomy recently introduced to western Europe via Spain, Bacon continued the work of Robert Grosseteste and criticised

8064-508: The intensity of the solar radiation decreases with depth into the gases. As a result, the cloud base can vary from a very light to very dark grey depending on the cloud's thickness and how much light is being reflected or transmitted back to the observer. Thin clouds may look white or appear to have acquired the color of their environment or background. High tropospheric and non-tropospheric clouds appear mostly white if composed entirely of ice crystals and/or supercooled water droplets. As

8176-460: The inversion layer's temperature gradient . The sunlight must bend to the Earth's curvature at least 400 kilometres (250 mi) to allow an elevation rise of 5 degrees for sight of the sun disk. The first person to record the phenomenon was Gerrit de Veer , a member of Willem Barentsz ' ill-fated third expedition into the polar region. Novaya Zemlya , the archipelago where de Veer first observed

8288-466: The known Greek and Arabic works on optics (then known as "perspective", perspectiva ). A passage in the Opus Tertium states that at some point he took a two-year break from his studies. By the late 1250s, resentment against the king 's preferential treatment of his émigré Poitevin relatives led to a coup and the imposition of the Provisions of Oxford and Westminster , instituting

8400-400: The left and right of the Sun, at a distance of about 22° and at the same elevation above the horizon. They are commonly caused by plate-shaped hexagonal ice crystals . These crystals tend to become horizontally aligned as they sink through the air, causing them to refract the sunlight to the left and right, resulting in the two sun dogs. As the Sun rises higher, the rays passing through

8512-405: The level of the observer, or on days with ground fog. The glory is related to the optical phenomenon anthelion . A rainbow is a narrow, multicoloured semicircular arc due to dispersion of white light by a multitude of drops of water, usually in the form of rain, when they are illuminated by sunlight. Hence, when conditions are right, a rainbow always appears in the section of sky directly opposite

8624-417: The longest-possible path through the air, yielding more scattering. The blueness is at the horizon because the blue light coming from great distances is also preferentially scattered. This results in a red shift of the distant light sources that is compensated by the blue hue of the scattered light in the line of sight. In other words, the red light scatters also; if it does so at a point a great distance from

8736-502: The many clergy, monks, and educators attacked by Bacon's 1271 Compendium Studii Philosophiae . Modern scholarship, however, notes that the first reference to Bacon's "imprisonment" dates from eighty years after his death on the charge of unspecified "suspected novelties" and finds it less than credible. Contemporary scholars who do accept Bacon's imprisonment typically associate it with Bacon's "attraction to contemporary prophesies", his sympathies for "the radical 'poverty' wing of

8848-616: The mathematical aspects of astronomy and music . His faculty colleagues included Robert Kilwardby , Albertus Magnus , and Peter of Spain , who may later become Pope as Pope John XXI . The Cornishman Richard Rufus was a scholarly opponent. In 1247 or soon after, he left his position in Paris. As a private scholar, his whereabouts for the next decade are uncertain but he was likely in Oxford c.  1248 –1251, where he met Adam Marsh , and in Paris in 1251. He seems to have studied most of

8960-505: The mid-1260s, he was undertaking a search for patrons who could secure permission and funding for his return to Oxford. For a time, Bacon was finally able to get around his superiors' interference through his acquaintance with Guy de Foulques , bishop of Narbonne , cardinal of Sabina , and the papal legate who negotiated between England's royal and baronial factions. In 1263 or 1264, a message garbled by Bacon's messenger, Raymond of Laon, led Guy to believe that Bacon had already completed

9072-497: The number of bands) are an artifact of human color vision , and no banding of any type is seen in a black-and-white photograph of a rainbow (only a smooth gradation of intensity to a maxima, then fading to a minima at the other side of the arc). For colors seen by a normal human eye, the most commonly cited and remembered sequence, in English, is Isaac Newton 's sevenfold red, orange, yellow, green, blue, indigo and violet (popularly memorized by mnemonics like Roy G. Biv ). A mirage

9184-619: The object often appears to be very unusual, and may even be transformed in such a way that it is completely unrecognizable. A Fata Morgana can be seen on land or at sea, in polar regions or in deserts. This kind of mirage can involve almost any kind of distant object, including such things as boats, islands, and coastline. A Fata Morgana is not only complex, but also rapidly changing. The mirage comprises several inverted (upside down) and erect (right side up) images that are stacked on top of one another. Fata Morgana mirages also show alternating compressed and stretched zones. The Novaya Zemlya effect

9296-489: The observance of fixed equinoxes and solstices was not acted upon following the death of Pope Clement IV in 1268. The eventual Gregorian calendar drops one day from the first three centuries in each set of 400 years. In Part V of the Opus Majus , Bacon discusses physiology of eyesight and the anatomy of the eye and the brain , considering light , distance, position, and size, direct and reflected vision, refraction , mirrors , and lenses . His treatment

9408-440: The observer it has a much higher chance of reaching the observer than blue light. At distances nearing infinity, the scattered light is therefore white. Distant clouds or snowy mountaintops will seem yellow for that reason; that effect is not obvious on clear days, but very pronounced when clouds are covering the line of sight reducing the blue hue from scattered sunlight. The scattering due to molecule sized particles (as in air)

9520-418: The ocean, but are possible over cloud tops and mountain tops as well. A green flash from the Moon and bright planets at the horizon, including Venus and Jupiter , can also be observed. This optical phenomenon occurs because rays of light are strongly bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed. A thermal inversion

9632-412: The optical properties of Earth's atmosphere cause a wide range of optical phenomena and visual perception phenomena. Examples of meteorological phenomena include: Other phenomena that are remarkable because they are forms of visual illusions include: A book on meteorological optics was published in the sixteenth century, but there have been numerous books on the subject since about 1950. The topic

9744-466: The origin and composition of metals, is traditionally credited to Bacon. It espouses the Arabian theory of mercury and sulphur forming the other metals, with vague allusions to transmutation . Stillman opined that "there is nothing in it that is characteristic of Roger Bacon's style or ideas, nor that distinguishes it from many unimportant alchemical lucubrations of anonymous writers of the thirteenth to

9856-576: The phenomenon, lends its name to the effect. Crepuscular rays are near-parallel rays of sunlight moving through the Earth's atmosphere, but appear to diverge because of linear perspective . They often occur when objects such as mountain peaks or clouds partially shadow the Sun's rays like a cloud cover . Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction , reflection, and scattering. Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in

9968-517: The positions and sizes of the celestial bodies . It is divided into seven sections: "The Four General Causes of Human Ignorance" ( Causae Erroris ), "The Affinity of Philosophy with Theology" ( Philosophiae cum Theologia Affinitas ), "On the Usefulness of Grammar" ( De Utilitate Grammaticae ), "The Usefulness of Mathematics in Physics" ( Mathematicae in Physicis Utilitas ), " On

10080-451: The practices of his contemporaries, arguing that "thence cometh quiet to the mind". Bacon also called for reform with regard to theology . He argued that, rather than training to debate minor philosophical distinctions, theologians should focus their attention primarily on the Bible itself, learning the languages of its original sources thoroughly. He was fluent in several of these languages and

10192-413: The preferred angular distance are 22 and 46 degrees from the ice crystals which create them. Atmospheric phenomena such as halos have been used as part of weather lore as an empirical means of weather forecasting , with their presence indicating an approach of a warm front and its associated rain . Sun dogs are a common type of halo, with the appearance of two subtly-colored bright spots to

10304-443: The result of the scattering of sunlight by the atmosphere. When the angle between the Sun and the horizon is less than 10 percent, as it is just after sunrise or just prior to sunset, sunlight becomes too red due to refraction for any colors other than those with a reddish hue to be seen. The clouds do not become that color; they are reflecting long and unscattered rays of sunlight, which are predominant at those hours. The effect

10416-413: The results he obtained were different from those that would have been predicted by Aristotle. His linguistic work has been heralded for its early exposition of a universal grammar , and 21st-century re-evaluations emphasise that Bacon was essentially a medieval thinker, with much of his "experimental" knowledge obtained from books in the scholastic tradition . He was, however, partially responsible for

10528-432: The same image size on the retina that appears far. With the overhead Moon, there is no uninterrupted sequence of intervening bodies. Hence it appears far and small. With a horizon Moon, there is an uninterrupted sequence of intervening bodies: all the objects between the observer and the horizon, so the Moon appears far and large. Through works by Roger Bacon , John Pecham , and Witelo based on Ibn al-Haytham's explanation,

10640-417: The senses) in [the sound and fire of] that children's toy which is made in many [diverse] parts of the world; i.e. a device no bigger than one's thumb. From the violence of that salt called saltpetre [together with sulphur and willow charcoal, combined into a powder] so horrible a sound is made by the bursting of a thing so small, no more than a bit of parchment [containing it], that we find [the ear assaulted by

10752-497: The short end of light's visible wavelengths, while red and yellow are at the long end. The short rays are more easily scattered by water droplets, and the long rays are more likely to be absorbed. The bluish color is evidence that such scattering is being produced by rain-sized droplets in the cloud. A cumulonimbus cloud emitting green is a sign that it is a severe thunderstorm , capable of heavy rain, hail , strong winds and possible tornadoes . The exact cause of green thunderstorms

10864-409: The sixteenth centuries", and Muir and Lippmann also considered it a pseudepigraph . The cryptic Voynich manuscript has been attributed to Bacon by various sources, including by its first recorded owner, but historians of science Lynn Thorndike and George Sarton dismissed these claims as unsupported, and the vellum of the manuscript has since been dated to the 15th century. Bacon

10976-405: The sky is a result of Rayleigh scattering of sunlight , which results in a perceived blue color. On a sunny day, Rayleigh scattering gives the sky a blue gradient , darkest around the zenith and brightest near the horizon. Light rays coming from the zenith take the shortest-possible path ( 1 ⁄ 38 ) through the air mass , yielding less scattering. Light rays coming from the horizon take

11088-488: The sky, most pronounced at an angle 90° from the Sun. Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Recent developments relate to “all sky models” for modelling sky luminance under weather conditions ranging from clear sky to overcast . The color of a cloud, as seen from the Earth, tells much about what

11200-458: The southeastern United States during the summer, which changes the sky from a blue to a white appearance and leads to an increase in red sunsets. Its presence negatively affects air quality during the summer since it adds to the count of airborne particulates. The sky can turn a multitude of colors such as red, orange, pink and yellow (especially near sunset or sunrise) and black at night. Scattering effects also partially polarize light from

11312-527: The sun dog finally merge into the white of the parhelic circle (if the latter is visible). It is theoretically possible to predict the forms of sun dogs as would be seen on other planets and moons. Mars might have sundogs formed by both water-ice and CO 2 -ice. On the giant gas planets — Jupiter , Saturn , Uranus and Neptune — other crystals form the clouds of ammonia , methane , and other substances that can produce halos with four or more sundogs. A common optical phenomenon involving water droplets

11424-464: The term "crepuscular rays" is sometimes extended to the general phenomenon of rays of sunlight that appear to converge at a point in the sky, irrespective of time of day. In some cases, sunbeams may extend across the sky and appear to converge at the antisolar point , the point on the celestial sphere opposite of the Sun's direction. In this case, they are called antisolar rays (anytime not during astronomical night) or anticrepuscular rays (during

11536-465: The then-current Julian calendar as "intolerable, horrible, and laughable". It had become apparent that Eudoxus and Sosigenes 's assumption of a year of 365¼ days was, over the course of centuries, too inexact. Bacon charged that this meant the computation of Easter had shifted forward by 9 days since the First Council of Nicaea in 325. His proposal to drop one day every 125 years and to cease

11648-467: The time were largely limited to addressing disputes on the known texts of Aristotle, Clement's patronage permitted Bacon to engage in a wide-ranging consideration of the state of knowledge in his era. In 1267 or '68, Bacon sent the Pope his Opus Majus , which presented his views on how to incorporate Aristotelian logic and science into a new theology, supporting Grosseteste's text-based approach against

11760-597: The upper troposphere , at an altitude of 5 kilometres (3.1 mi) to 10 kilometres (6.2 mi), or, during very cold weather, by ice crystals called diamond dust drifting in the air at low levels. The particular shape and orientation of the crystals are responsible for the types of halo observed. Light is reflected and refracted by the ice crystals and may split into colors because of dispersion . The crystals behave like prisms and mirrors , refracting and reflecting sunlight between their faces, sending shafts of light in particular directions. For circular halos,

11872-466: Was able to note and bemoan several corruptions of scripture, and of the works of the Greek philosophers that had been mistranslated or misinterpreted by scholars working in Latin. He also argued for the education of theologians in science (" natural philosophy ") and its addition to the medieval curriculum . Bacon's 1267 Greater Work , the Opus Majus , contains treatments of mathematics , optics , alchemy , and astronomy , including theories on

11984-407: Was largely ignored by his contemporaries in favour of other scholars such as Albertus Magnus , Bonaventure , and Thomas Aquinas , although his works were studied by Bonaventure, John Pecham , and Peter of Limoges , through whom he may have influenced Raymond Lull . He was also partially responsible for the addition of optics ( perspectiva ) to the medieval university curriculum . By

12096-509: Was popularised by the wide circulation of a book by Marcel Minnaert , Light and Color in the Open Air , in 1954. In the Book of Optics (1011–22 AD), Ibn al-Haytham argued that vision occurs in the brain, and that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. Arguing against Ptolemy 's refraction theory for why people perceive

12208-443: Was primarily oriented by the Latin translation of Alhazen 's Book of Optics . He also draws heavily on Eugene of Palermo 's Latin translation of the Arabic translation of Ptolemy 's Optics ; on Robert Grosseteste 's work based on Al-Kindi 's Optics ; and, through Alhazen ( Ibn al-Haytham ), on Ibn Sahl 's work on dioptrics . A passage in the Opus Majus and another in the Opus Tertium are usually taken as

12320-652: Was received at Paris as an authority equal to Aristotle, Avicenna and Averroes , a situation Bacon decried: "never in the world [had] such monstrosity occurred before." In Part I of the Opus Majus Bacon recognises some philosophers as the Sapientes , or gifted few, and saw their knowledge in philosophy and theology as superior to the vulgus philosophantium , or common herd of philosophers. He held Islamic thinkers between 1210 and 1265 in especially high regard calling them "both philosophers and sacred writers" and defended

12432-427: Was regarded as a wizard and particularly famed for the story of his mechanical or necromantic brazen head . He is credited as one of the earliest European advocates of the modern scientific method , along with his teacher Robert Grosseteste . Bacon applied the empirical method of Ibn al-Haytham (Alhazen) to observations in texts attributed to Aristotle . Bacon discovered the importance of empirical testing when

12544-498: Was the most important science. The reason why Bacon kept the topic of alchemy vague for the most part, is due to the need for secrecy about esoteric topics in England at the time as well as his dedication to remaining in line with the alchemical tradition of speaking in symbols and metaphors. Bacon's early linguistic and logical works are the Overview of Grammar ( Summa Grammatica ), Summa de Sophismatibus et Distinctionibus , and

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