The Danjon Scale is a five-point scale for measuring the appearance and luminosity of a particular heavenly body during what type of event?
"eruptions are one of the most significant - eruptions which spew significant amounts of volcanic ash into the air are generally followed by several years of dark, deep red eclipses. The effect of the eruption of Mount Pinatubo on subsequent lunar eclipses was very noticeable, with the eclipse of 9 December 1992 rated 0 on the Danjon Scale by many observers. It is also thought that the solar cycle has some effect on the darkness of lunar eclipses--indeed Danjon established the scale for this reason. Danjon scale The Danjon Scale is a five-point scale useful for measuring the appearance and"
"a proposed measure of the minimum angular separation of the Sun and Moon at which a lunar crescent is visible. However, this limit may not exist. He was Director of the Observatory of Strasbourg from 1930 to 1945 and of the Paris Observatory from 1945 to 1963 (see biographical notice at the website of the Observatoire de Paris https://web.archive.org/web/20110927074250/http://www.obspm.fr/histoire/paris/danjon.fr.shtml). Danjon was the President of the Société astronomique de France (SAF), the French astronomical society, from 1947-1949 and from 1962-1964. He was awarded the Prix Jules Janssen of the Société astronomique de France in 1950, and the Gold Medal of the"
"nearly opposite points in the sky. This arrangement has led to the phenomenon being also called a horizontal eclipse. Typically, a number of high ridges undergoing sunrise or sunset can view it. Although the Moon is in Earth's umbra, both the Sun and an eclipsed Moon can be simultaneously seen because atmospheric refraction causes each body to appear higher in the sky than their true geometric positions. The following scale (the Danjon scale) was devised by André Danjon for rating the overall darkness of lunar eclipses: There is often confusion between a solar eclipse and a lunar eclipse. While both"
"Bortle scale The Bortle scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of ""Sky & Telescope"" magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye"
"using his method (now known as the Danjon Scale, on which zero equates to a barely visible Moon) from 1925 until the 1950s. Among his notable contributions to astronomy was the design of the impersonal (prismatic) astrolabe now known as the Danjon astrolabe, which led to an improvement in the accuracy of fundamental optical astrometry. An account of this instrument, and of the results of some early years of its operation, are given in Danjon's 1958 George Darwin Lecture to the Royal Astronomical Society (in Monthly Notices of the RAS (1958), vol.118, pages 411-431). He also developed the Danjon Limit,"
"André-Louis Danjon André-Louis Danjon (6 April 1890 – 21 April 1967) was a French astronomer born in Caen to Louis Dominique Danjon and Marie Justine Binet. Danjon devised a method to measure ""Earthshine"" on the Moon using a telescope in which a prism split the Moon's image into two identical side-by-side images. By adjusting a diaphragm to dim one of the images until the sunlit portion had the same apparent brightness as the earthlit portion on the unadjusted image, he could quantify the diaphragm adjustment, and thus had a real measurement for the brightness of Earthshine. He recorded the measurements"
"astronomers have been debating whether a new system with more categories is necessary. The scale is a five-point system, with 1 being the best seeing conditions and 5 being the worst. The actual definitions are as follows: Note that the scale is usually indicated by use of a Roman numeral or an ordinary number. Astronomers have devised several methods for defining the quality of seeing apart from the Antoniadi scale, including: Antoniadi scale The Antoniadi scale is a system used by amateur astronomers to categorise the weather conditions when viewing the stars at night. The Antoniadi scale was invented by"
"limiting magnitude (NELM). The accuracy and utility of the scale have been questioned in recent research. The table below summarizes Bortle's descriptions of the classes. Bortle scale The Bortle scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of ""Sky & Telescope"" magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The"
"Royal Astronomical Society in 1958. Danjon died in 1967 in Suresnes, Hauts-de-Seine. André-Louis Danjon André-Louis Danjon (6 April 1890 – 21 April 1967) was a French astronomer born in Caen to Louis Dominique Danjon and Marie Justine Binet. Danjon devised a method to measure ""Earthshine"" on the Moon using a telescope in which a prism split the Moon's image into two identical side-by-side images. By adjusting a diaphragm to dim one of the images until the sunlit portion had the same apparent brightness as the earthlit portion on the unadjusted image, he could quantify the diaphragm adjustment, and thus had"
"Apparent magnitude The apparent magnitude () of an astronomical object is a number that is 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 , or about 2.512. The brighter an object appears, the lower its magnitude value (i.e. inverse relation), 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"
"Culmination In observational astronomy, the culmination of a celestial object (the Sun, the Moon, a planet, a star, or a deep-sky object) or constellation is either of two moments when it reaches the observer's meridian on the celestial sphere, on which it appears to move along a circular path over the course of a day, due to Earth's rotation. As viewed from the surface of a terrestrial body, except its geographic poles, a celestial object passes through the meridian twice a day: once at its upper culmination, when it reaches its highest point as viewed from a given location on"
"the sky during the night. Celestial objects are found by adjusting the telescope's or other instrument's scales so that they match the equatorial coordinates of the selected object to observe. Popular choices of pole and equator are the older B1950 and the modern J2000 systems, but a pole and equator ""of date"" can also be used, meaning one appropriate to the date under consideration, such as when a measurement of the position of a planet or spacecraft is made. There are also subdivisions into ""mean of date"" coordinates, which average out or ignore nutation, and ""true of date,"" which include"
"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 the level of the observer, or on days with ground fog. The glory is related to the optical phenomenon anthelion. A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicolored arc. Rainbows caused by sunlight always appear in the"
"degrees apart in the sky at its closest. Conjunction (astronomy) In astronomy, a conjunction occurs when two astronomical objects or spacecraft have either the same right ascension or the same ecliptic longitude, usually as observed from Earth. The astronomical symbol for conjunction is ☌ (in Unicode U+260C) and handwritten . The conjunction symbol is not used in modern astronomy. It continues to be used in astrology. When two objects always appear close to the ecliptic—such as two planets, the Moon and a planet, or the Sun and a planet—this fact implies an apparent close approach between the objects as seen"
"at the March equinox and is currently located in the constellation Pisces. Right ascension is measured continuously in a full circle from that alignment of earth and sun in space, that equinox, the measurement increasing towards the east. Apart from at the poles, as seen from earth, objects noted to have 12 are longest visible (appear throughout the night) at the March Equinox; those with 0 (apart from the sun) do so at the September Equinox. On those dates at midnight, such objects will reach (""culminate"" at) their highest point (their meridian). How high depends on their declination; if 0°"
"from the observer's latitude, are described as circumpolar. Culmination In observational astronomy, the culmination of a celestial object (the Sun, the Moon, a planet, a star, or a deep-sky object) or constellation is either of two moments when it reaches the observer's meridian on the celestial sphere, on which it appears to move along a circular path over the course of a day, due to Earth's rotation. As viewed from the surface of a terrestrial body, except its geographic poles, a celestial object passes through the meridian twice a day: once at its upper culmination, when it reaches its highest"
"Astronomical seeing Astronomical seeing refers to the amount of apparent blurring and twinkling of astronomical objects like stars due to turbulent mixing in the atmosphere of Earth, causing variations of the optical refractive index. The seeing conditions on a given night at a given location describe how much Earth's atmosphere perturbs the images of stars as seen through a telescope. The most common seeing measurement is the full width at half maximum (FWHM) of the optical intensity across the ""seeing disc"" (the point spread function for imaging through the atmosphere). The FWHM of the point spread function (loosely called seeing"
"although this can be very uncomfortable and cause long-lasting afterimages. In astronomy, the illuminance stars cast on the Earth's atmosphere is used as a measure of their brightness. The usual units are apparent magnitudes in the visible band. V-magnitudes can be converted to lux using the formula where ""E"" is the illuminance in lux, and ""M"" is the apparent magnitude. The reverse conversion is Illuminance In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate"
"to an earthquake measuring 5.0 on the Richter magnitude scale. Over the next few days night skies in Asia and Europe were aglow, with contemporaneous reports of photographs being successfully taken at midnight in both Sweden and Scotland. It has been theorized that this effect was due to light passing through high-altitude ice particles that had formed at extremely low temperatures—a phenomenon that many years later would be produced by space shuttles. In the United States, the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a months-long decrease in atmospheric transparency due to an increase in suspended dust particles."
"Twinkling Twinkling, or scintillation, is a generic term for variations in apparent brightness or position of a distant luminous object viewed through a medium. If the object lies outside the Earth's atmosphere, as in the case of stars and planets, the phenomenon is termed ""astronomical scintillation""; within the atmosphere, the phenomenon is termed ""terrestrial scintillation."" As one of the three principal factors governing astronomical seeing (the others being light pollution and cloud cover), atmospheric twinkling is defined as variations in illuminance only. In simple terms, twinkling of stars is caused by the passing of light through different layers of a"
"most conditions, these are not observed. However, under some circumstances lights from moving vehicles, aircraft, ships, buildings, etc. can be observed at night, even though, as with a daytime mirage, they would not be observable. This includes the mirage of astronomical objects. A mirage of an astronomical object is a naturally occurring optical phenomenon, in which light rays are bent to produce distorted or multiple images of an astronomical object. The mirages might be observed for such astronomical objects as the Sun, the Moon, the planets, bright stars, and very bright comets. The most commonly observed are sunset and sunrise"
"Eclipse An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. Apart from syzygy, the term eclipse is also used when a spacecraft reaches a position where it can observe two celestial bodies so aligned. An eclipse is the result of either an occultation (completely hidden) or a transit (partially hidden). The term eclipse is most often used to describe either a solar eclipse,"
"Magnitude (astronomy) In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. The scale is logarithmic and defined such that each step of one magnitude changes the brightness by a factor of the fifth root of 100, or approximately 2.512. For example, a magnitude 1 star is exactly 100 times brighter than a magnitude 6 star. The brighter an object appears, the lower the"
"a hot patch and a cold patch on the sky - depends on the curvature of the universe which in turn depends on its density as described above. Thus, measurements of this angular scale allow an estimation of Ω. Another probe of Ω is the frequency of Type-Ia supernovae at different distances from Earth. These supernovae, the explosions of degenerate white dwarf stars, are a type of standard candle; this means that the processes governing their intrinsic brightness are well understood so that a measure of ""apparent"" brightness when seen from Earth can be used to derive accurate distance measures"
"appear, with Venus (the second-brightest celestial object after the Moon in the night sky) visible above the horizon opposite of the Belt of Venus around the antisolar point. After the 1883 eruption of the volcano Krakatoa, a remarkable series of red sunsets appeared worldwide. An enormous amount of exceedingly fine dust were blown to a great height by the volcano's explosion, and then globally diffused by the high atmospheric winds. Edvard Munch's painting ""The Scream"" possibly depicts an afterglow during this period. Afterglow An afterglow is a broad arch of whitish or pinkish sunlight in the sky that is scattered"
"of reddish or orange lights in the sky, comprising four lights together and a fifth light trailing them. Each of the individual lights in the formation appeared to the witness to consist of two separate point sources of orange light. He returned home and through binoculars watched the lights until they disappeared south over the horizon. Lights were also reportedly seen in the areas of Prescott and Prescott Valley. At approximately 20:17 MST, callers began reporting the object was definitely solid, because it blocked out much of the starry sky as it passed over. John Kaiser was standing outside with"
"Mirage of astronomical objects A mirage of an astronomical object is an atmospheric optical phenomenon, in which light rays are bent to produce distorted or multiple images of an astronomical object. The mirages might be observed for such celestial objects as the Sun, the Moon, the planets, bright stars, and very bright comets. The most commonly observed of these are sunset and sunrise mirages. Mirages are distinguished from other phenomena caused by atmospheric refraction. One of the most prominent features of mirages is that a mirage might only produce images vertically, not sideways, while a simple refraction might distort and"
"to be detected by eye in a small amateur scope. But a much more obscure and relatively 'tiny' object—one which is readily seen in dark skies by amateur telescopes, under good conditions—is the newly discovered nebula (likely reflection type) associated with the star 4 Cygni (HD 183056): an approximately fan-shaped glowing region of several arcminutes' diameter, to the south and west of the fifth-magnitude star. It was first discovered visually near San Jose, California and publicly reported by amateur astronomer Stephen Waldee in 2007, and was confirmed photographically by Al Howard in 2010. California amateur astronomer Dana Patchick also says"
"was particularly intense in December 1956, and is thought related to the breakup of the short-period comet 289P/Blanpain. It peaks around 4–5 December, though is not seen every year. A very minor meteor shower peaks around July 14 with around one meteor an hour, though meteors can be seen anytime from July 3 to 18; this shower is referred to as the July Phoenicids. Phoenix (constellation) Phoenix is a minor constellation in the southern sky. Named after the mythical phoenix, it was first depicted on a celestial atlas by Johann Bayer in his 1603 ""Uranometria"". The French explorer and astronomer"
"ISS is the brightest artificial object in the sky, excluding flares, with an approximate maximum magnitude of −4 when overhead (similar to Venus). The ISS, like many satellites including the Iridium constellation, can also produce flares of up to 8 or 16 times the brightness of Venus as sunlight glints off reflective surfaces. The ISS is also visible in broad daylight, albeit with a great deal more difficulty. Tools are provided by a number of websites such as Heavens-Above (see ""Live viewing"" below) as well as smartphone applications that use orbital data and the observer's longitude and latitude to indicate"
"Meridian altitude Meridian altitude is a method of celestial navigation to calculate an observer's latitude. It notes the angular height of an astronomical object above the horizon at culmination. Meridian altitude is the simplest calculation of celestial navigation, in which an observer determines his latitude by measuring the altitude of an astronomical object at the time of its meridian contact. A meridian contact is the moment when the object contacts the observer's meridian, i.e. the imaginary line running north–south and through the zenith, nadir, and celestial poles. This is usually done with the equinox Sun at solar noon to determine"
"Conjunction (astronomy) In astronomy, a conjunction occurs when two astronomical objects or spacecraft have either the same right ascension or the same ecliptic longitude, usually as observed from Earth. The astronomical symbol for conjunction is ☌ (in Unicode U+260C) and handwritten . The conjunction symbol is not used in modern astronomy. It continues to be used in astrology. When two objects always appear close to the ecliptic—such as two planets, the Moon and a planet, or the Sun and a planet—this fact implies an apparent close approach between the objects as seen on the sky. A related word, ""appulse"", is"
"distance of just , and is therefore one of Earth's nearest stellar neighbours. Procyon is the eighth-brightest point of light in the night sky, culminating at midnight on January 14. It forms one of the three vertices of the Winter Triangle asterism, in combination with Sirius and Betelgeuse. The prime period for evening viewing of Procyon is in late winter in the northern hemisphere. It has a color index of 0.42, and its hue has been described as having a faint yellow tinge to it. Procyon is a binary star system with a bright primary component, Procyon A, having an"