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78-640: Hawaiʻiloa was an expert fisherman and navigator who was famous for his lengthy fishing expeditions. While on a prolonged voyage, his principal navigator, Makaliʻi, asked Hawaiʻiloa to steer eastward towards Aldebaran (Hokuʻula, meaning "red star") and the Pleiades (near the Cluster of Makaliʻi ). After sailing in this direction, he and his crew stumbled upon the island of Hawaiʻi, which was named in Hawaiʻiloa's honor. Hawaiʻiloa returned to his homeland, Ka ʻāina kai melemele

156-424: A corona and hence is not a source of hard X-ray emission . However, small scale magnetic fields may still be present in the lower atmosphere, resulting from convection turbulence near the surface. The measured strength of the magnetic field on Aldebaran is 0.22  G . Any resulting soft X-ray emissions from this region may be attenuated by the chromosphere , although ultraviolet emission has been detected in

234-469: A 643-day orbit at a separation of 2.0 AU (300 Gm) in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. In 2015 a study showed stable long-term evidence for both a planetary companion and stellar activity. An asteroseismic analysis of

312-497: A Kāne ("the land of the yellow sea of Kāne "), to bring his family back with him to Hawaiʻi. He then organized a colonizing expedition with his family and eight other skilled navigators. They settled on what is now the Island of Hawaiʻi , named in his honor. The legend contains reference to his children: Māui (his eldest son), Kauaʻi (son), and Oʻahu (daughter) who settled on the islands that bear their names. The Hawaiʻiloa legend

390-569: A close distance to Aldebaran and similar proper motions. With a parallax of 47.25  milliarcseconds , this translates into a distance of 21.16  pc (69.0  ly ). The NASA Exoplanet Archive recognizes Aldebaran as a binary star, with Aldebaran B being the secondary star. A spectral type of M2.5 has been published for Alpha Tauri B. Alpha Tauri CD is a binary system with the C and D component stars gravitationally bound to and co-orbiting each other. These co-orbiting stars have been shown to be located far beyond Aldebaran and are members of

468-450: A de facto standard in modern astronomy to describe differences in brightness. Defining and calibrating what magnitude 0.0 means is difficult, and different types of measurements which detect different kinds of light (possibly by using filters) have different zero points. Pogson's original 1856 paper defined magnitude 6.0 to be the faintest star the unaided eye can see, but the true limit for faintest possible visible star varies depending on

546-574: A distance of approximately 65 light-years from the Sun. The star lies along the line of sight to the nearby Hyades cluster . Aldebaran is a red giant , meaning that it is cooler than the Sun with a surface temperature of 3,900  K , but its radius is about 45 times the Sun's , so it is over 400 times as luminous . As a giant star , it has moved off the main sequence on the Hertzsprung–Russell diagram after depleting its supply of hydrogen in

624-551: A giant star, but around 25 times lower than the Earth's and 700 times lower than the Sun's. Its metallicity is about 30% lower than the Sun 's. Measurements by the Hipparcos satellite and other sources put Aldebaran around 65.3 light-years (20.0 parsecs) away. Asteroseismology has determined that it is about 16% more massive than the Sun, yet it shines with 518 times the Sun's luminosity due to

702-468: A given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. For objects at very great distances (far beyond the Milky Way), this relationship must be adjusted for redshifts and for non-Euclidean distance measures due to general relativity . For planets and other Solar System bodies, the apparent magnitude is derived from its phase curve and

780-466: A magnitude 3.0 star, 6.31 times as magnitude 4.0, and 100 times magnitude 7.0. The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46. The faintest stars visible with the naked eye on the darkest night have apparent magnitudes of about +6.5, though this varies depending on a person's eyesight and with altitude and atmospheric conditions. The apparent magnitudes of known objects range from

858-408: A smaller amplitude, with some showing almost no variation. Hipparcos photometry shows an amplitude of only about 0.02 magnitudes and a possible period around 18 days. Intensive ground-based photometry showed variations of up to 0.03 magnitudes and a possible period around 91 days. Analysis of observations over a much longer period still find a total amplitude likely to be less than 0.1 magnitudes, and

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936-599: A star's radial velocity from the amount of Doppler shift in the spectrum. By this means, the recession velocity of Aldebaran was estimated as 30 miles per second (48 km/s), using measurements performed at Potsdam Observatory by Hermann C. Vogel and his assistant Julius Scheiner . Aldebaran was observed using an interferometer attached to the Hooker Telescope at the Mount Wilson Observatory in 1921 in order to measure its angular diameter , but it

1014-486: Is a giant star that has evolved off the main sequence band of the HR diagram after exhausting the hydrogen at its core. The collapse of the center of the star into a degenerate helium core has ignited a shell of hydrogen outside the core and Aldebaran is now on the red giant branch (RGB). The effective temperature of Aldebaran's photosphere is 3,910  K . It has a surface gravity of 1.59  cgs , typical for

1092-457: Is a star located in the zodiac constellation of Taurus . It has the Bayer designation α Tauri , which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from an apparent visual magnitude 0.75 down to 0.95, making it the brightest star in the constellation, as well as (typically) the fourteenth-brightest star in the night sky. It is positioned at

1170-567: Is a popular subject for ancient and modern myths. As the brightest star in a Zodiac constellation, it is given great significance within astrology . Irish singer and composer, Enya, has written a piece called “Aldebaran” after the star. The name Aldebaran or Alpha Tauri has been adopted many times, including The star also appears in works of fiction such as Far from the Madding Crowd (1874) and Down and Out in Paris and London (1933). It

1248-473: Is accurately known. Moreover, as the amount of light actually received by a telescope is reduced due to transmission through the Earth's atmosphere , the airmasses of the target and calibration stars must be taken into account. Typically one would observe a few different stars of known magnitude which are sufficiently similar. Calibrator stars close in the sky to the target are favoured (to avoid large differences in

1326-613: Is defined such that an object's AB and Vega-based magnitudes will be approximately equal in the V filter band. However, the AB magnitude system is defined assuming an idealized detector measuring only one wavelength of light, while real detectors accept energy from a range of wavelengths. Precision measurement of magnitude (photometry) requires calibration of the photographic or (usually) electronic detection apparatus. This generally involves contemporaneous observation, under identical conditions, of standard stars whose magnitude using that spectral filter

1404-612: Is frequently seen in science fiction , including the Lensman series (1948–1954), Fallen Dragon (2001) and passingly in Kim Stanley Robinson's "Blue Mars" (1996). Aldebaran is associated with Hastur , also known as The King in Yellow, in the horror stories of Robert W. Chambers . Aldebaran regularly features in conspiracy theories as one of the origins of extraterrestrial aliens , often linked to Nazi UFOs . A well-known example

1482-417: Is of greater use in stellar astrophysics since it refers to a property of a star regardless of how close it is to Earth. But in observational astronomy and popular stargazing , references to "magnitude" are understood to mean apparent magnitude. Amateur astronomers commonly express the darkness of the sky in terms of limiting magnitude , i.e. the apparent magnitude of the faintest star they can see with

1560-419: Is often called "Vega normalized", Vega is slightly dimmer than the six-star average used to define magnitude 0.0, meaning Vega's magnitude is normalized to 0.03 by definition. With the modern magnitude systems, brightness is described using Pogson's ratio. In practice, magnitude numbers rarely go above 30 before stars become too faint to detect. While Vega is close to magnitude 0, there are four brighter stars in

1638-600: Is popular amongst Hawaiians as a realistic Hawaiian origin story that is consistent with modern anthropological and historical beliefs. However, there is currently little evidence to support its historical accuracy. The story is attested only by 19th-century sources such as Abraham Fornander and Thomas George Thrum , neither of whom provided their sources. Hawaiʻiloa is also unmentioned by earlier Hawaiian historians such as David Malo . Malo chronicled many Hawaiian origin stories, migration tales, and legends of indigenous origin. Samuel Kamakau tells of an alternate legend that

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1716-399: Is that the logarithmic nature of the scale is because the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber–Fechner law ), but it is now believed that the response is a power law (see Stevens' power law ) . Magnitude is complicated by the fact that light is not monochromatic . The sensitivity of a light detector varies according to

1794-597: Is the German conspiracy theorist Axel Stoll , who considered the star the home of the Aryan race and the target of expeditions by the Wehrmacht . The planetary exploration probe Pioneer 10 is no longer powered or in contact with Earth, but its trajectory is taking it in the general direction of Aldebaran. It is expected to make its closest approach in about two million years. The Austrian chemist Carl Auer von Welsbach proposed

1872-457: Is the observed irradiance using spectral filter x , and F x ,0 is the reference flux (zero-point) for that photometric filter . Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 100 5 ≈ 2.512 {\displaystyle {\sqrt[{5}]{100}}\approx 2.512} (Pogson's ratio). Inverting

1950-759: Is the ratio in brightness between the Sun and the full Moon ? The apparent magnitude of the Sun is −26.832 (brighter), and the mean magnitude of the full moon is −12.74 (dimmer). Difference in magnitude: x = m 1 − m 2 = ( − 12.74 ) − ( − 26.832 ) = 14.09. {\displaystyle x=m_{1}-m_{2}=(-12.74)-(-26.832)=14.09.} Brightness factor: v b = 10 0.4 x = 10 0.4 × 14.09 ≈ 432 513. {\displaystyle v_{b}=10^{0.4x}=10^{0.4\times 14.09}\approx 432\,513.} The Sun appears to be approximately 400 000 times as bright as

2028-420: Is the resulting magnitude after adding the brightnesses referred to by m 1 and m 2 . While magnitude generally refers to a measurement in a particular filter band corresponding to some range of wavelengths, the apparent or absolute bolometric magnitude (m bol ) is a measure of an object's apparent or absolute brightness integrated over all wavelengths of the electromagnetic spectrum (also known as

2106-739: The Aitken Double Star Catalogue as ADS 3321. It was included with an 11th-magnitude companion as a double star as H IV 66 in the Herschel Catalogue of Double Stars and Σ II 2 in the Struve Double Star Catalog , and together with a 14th-magnitude star as β 550 in the Burnham Double Star Catalogue . Aldebaran is one of the easiest stars to find in the night sky , partly due to its brightness and partly due to being near one of

2184-539: The Hipparcos catalogue number 21421, mostly seen in scientific publications. It is a variable star listed in the General Catalogue of Variable Stars , but it is listed using its Bayer designation and does not have a separate variable star designation . Aldebaran and several nearby stars are included in double star catalogues such as the Washington Double Star Catalog as WDS 04359+1631 and

2262-597: The Marquesas Islands in company with Hōkūleʻa and a third canoe from Hawaiʻi called Makaliʻi together with two canoes from Rarotonga : Te ʻAu Tonga and Takitumu , and the canoe Te ʻAurere , from New Zealand . Subsequently that year, Hawaiʻiloa was shipped to Seattle and then sailed north to Alaska, visiting twenty native villages on the coastal journey between Vancouver and Juneau . Aldebaran Aldebaran ( Arabic : الدَّبَران , lit.   'The Follower') (Proto-Semitic *dVbr- “bee”)

2340-459: The apparent visual magnitude . Absolute magnitude is a related quantity which measures the luminosity that a celestial object emits, rather than its apparent brightness when observed, and is expressed on the same reverse logarithmic scale. Absolute magnitude is defined as the apparent magnitude that a star or object would have if it were observed from a distance of 10 parsecs (33 light-years; 3.1 × 10 kilometres; 1.9 × 10 miles). Therefore, it

2418-569: The core . The star spins slowly and takes 520 days to complete a rotation. Aldebaran is believed to host a planet several times the mass of Jupiter , named Aldebaran b . The traditional name Aldebaran derives from the Arabic al Dabarān ( الدبران ), meaning ' the follower ' , because it seems to follow the Pleiades . In 2016, the International Astronomical Union Working Group on Star Names (WGSN) approved

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2496-437: The intrinsic brightness of an object. Flux decreases with distance according to an inverse-square law , so the apparent magnitude of a star depends on both its absolute brightness and its distance (and any extinction). For example, a star at one distance will have the same apparent magnitude as a star four times as bright at twice that distance. In contrast, the intrinsic brightness of an astronomical object, does not depend on

2574-472: The spectrum . The star is currently losing mass at a rate of (1–1.6) × 10   M ☉ /yr (about one Earth mass in 300,000 years) with a velocity of 30 km/s . This stellar wind may be generated by the weak magnetic fields in the lower atmosphere. Beyond the chromosphere of Aldebaran is an extended molecular outer atmosphere ( MOLsphere ) where the temperature is cool enough for molecules of gas to form. This region lies at about 2.5 times

2652-458: The table below. Astronomers have developed other photometric zero point systems as alternatives to Vega normalized systems. The most widely used is the AB magnitude system, in which photometric zero points are based on a hypothetical reference spectrum having constant flux per unit frequency interval , rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zero point

2730-489: The Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way. In 1993 radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion . The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that of Jupiter in

2808-576: The Sun at −26.832 to objects in deep Hubble Space Telescope images of magnitude +31.5. The measurement of apparent magnitude is called photometry . Photometric measurements are made in the ultraviolet , visible , or infrared wavelength bands using standard passband filters belonging to photometric systems such as the UBV system or the Strömgren uvbyβ system . Measurement in the V-band may be referred to as

2886-430: The above formula, a magnitude difference m 1 − m 2 = Δ m implies a brightness factor of F 2 F 1 = 100 Δ m 5 = 10 0.4 Δ m ≈ 2.512 Δ m . {\displaystyle {\frac {F_{2}}{F_{1}}}=100^{\frac {\Delta m}{5}}=10^{0.4\Delta m}\approx 2.512^{\Delta m}.} What

2964-447: The absolute magnitude H rather means the apparent magnitude it would have if it were 1 astronomical unit (150,000,000 km) from both the observer and the Sun, and fully illuminated at maximum opposition (a configuration that is only theoretically achievable, with the observer situated on the surface of the Sun). The magnitude scale is a reverse logarithmic scale. A common misconception

3042-516: The atmosphere and how high a star is in the sky. The Harvard Photometry used an average of 100 stars close to Polaris to define magnitude 5.0. Later, the Johnson UVB photometric system defined multiple types of photometric measurements with different filters, where magnitude 0.0 for each filter is defined to be the average of six stars with the same spectral type as Vega. This was done so the color index of these stars would be 0. Although this system

3120-476: The atmospheric paths). If those stars have somewhat different zenith angles ( altitudes ) then a correction factor as a function of airmass can be derived and applied to the airmass at the target's position. Such calibration obtains the brightness as would be observed from above the atmosphere, where apparent magnitude is defined. The apparent magnitude scale in astronomy reflects the received power of stars and not their amplitude. Newcomers should consider using

3198-498: The blue and UV regions of the spectrum, their power is often under-represented by the UBV scale. Indeed, some L and T class stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in infrared . Measures of magnitude need cautious treatment and it is extremely important to measure like with like. On early 20th century and older orthochromatic (blue-sensitive) photographic film ,

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3276-413: The blue region) and V (about 555 nm, in the middle of the human visual range in daylight). The V band was chosen for spectral purposes and gives magnitudes closely corresponding to those seen by the human eye. When an apparent magnitude is discussed without further qualification, the V magnitude is generally understood. Because cooler stars, such as red giants and red dwarfs , emit little energy in

3354-544: The brightness of stars was popularized by Ptolemy in his Almagest and is generally believed to have originated with Hipparchus . This cannot be proved or disproved because Hipparchus's original star catalogue is lost. The only preserved text by Hipparchus himself (a commentary to Aratus) clearly documents that he did not have a system to describe brightness with numbers: He always uses terms like "big" or "small", "bright" or "faint" or even descriptions such as "visible at full moon". In 1856, Norman Robert Pogson formalized

3432-532: The canoe, two Sitka spruce logs were brought to Hawaiʻi from Southeast Alaska , donated by the SeAlaska Corporation (owned by the Tlingit , Haida , and Tshimshian tribes). These came from 400-year-old, 200 feet high trees, a size which could not be found in modern Hawaiʻi. The hulls of the canoe were designed by Rudy and Barry Choy and Dick Rhodes, and also used numerous woods from more local sources. The canoe

3510-497: The cluster that forms the bull's-head-shaped asterism is more than twice as far away, at about 150 light years. Aldebaran is 5.47 degrees south of the ecliptic and so can be occulted by the Moon . Such occultations occur when the Moon's ascending node is near the autumnal equinox . A series of 49 occultations occurred starting on 29 January 2015 and ending at 3 September 2018. Each event

3588-449: The distance of the observer or any extinction . The absolute magnitude M , of a star or astronomical object is defined as the apparent magnitude it would have as seen from a distance of 10 parsecs (33  ly ). The absolute magnitude of the Sun is 4.83 in the V band (visual), 4.68 in the Gaia satellite's G band (green) and 5.48 in the B band (blue). In the case of a planet or asteroid,

3666-541: The expanded radius. The angular diameter of Aldebaran has been measured many times. The value adopted as part of the Gaia benchmark calibration is 20.580 ± 0.030  mas . It is 44 times the diameter of the Sun , approximately 61 million kilometres. Aldebaran is a slightly variable star , assigned to the slow irregular type LB . The General Catalogue of Variable Stars indicates variation between apparent magnitude 0.75 and 0.95 from historical reports. Modern studies show

3744-570: The first man ( Kumu-Honua ) and woman ( Lalo-Honua ) were created on Oʻahu. Hawaiʻiloa is also the name of a voyaging canoe, built between 1991 and 1994. Named after the legendary navigator, the canoe was built for ocean navigation and has sailed internationally. The canoe Hawaiʻiloa is now docked at Honolulu Harbor . It is often sailed on long voyages throughout the Pacific Ocean , studying voyaging techniques used in Ancient Hawaii . To make

3822-1162: The full Moon. Sometimes one might wish to add brightness. For example, photometry on closely separated double stars may only be able to produce a measurement of their combined light output. To find the combined magnitude of that double star knowing only the magnitudes of the individual components, this can be done by adding the brightness (in linear units) corresponding to each magnitude. 10 − m f × 0.4 = 10 − m 1 × 0.4 + 10 − m 2 × 0.4 . {\displaystyle 10^{-m_{f}\times 0.4}=10^{-m_{1}\times 0.4}+10^{-m_{2}\times 0.4}.} Solving for m f {\displaystyle m_{f}} yields m f = − 2.5 log 10 ⁡ ( 10 − m 1 × 0.4 + 10 − m 2 × 0.4 ) , {\displaystyle m_{f}=-2.5\log _{10}\left(10^{-m_{1}\times 0.4}+10^{-m_{2}\times 0.4}\right),} where m f

3900-527: The lines of nine elements, including iron , sodium , calcium , and magnesium . In 1886, Edward C. Pickering at the Harvard College Observatory used a photographic plate to capture fifty absorption lines in the spectrum of Aldebaran. This became part of the Draper Catalogue , published in 1890. By 1887, the photographic technique had improved to the point that it was possible to measure

3978-647: The magnitude m , in the spectral band x , would be given by m x = − 5 log 100 ⁡ ( F x F x , 0 ) , {\displaystyle m_{x}=-5\log _{100}\left({\frac {F_{x}}{F_{x,0}}}\right),} which is more commonly expressed in terms of common (base-10) logarithms as m x = − 2.5 log 10 ⁡ ( F x F x , 0 ) , {\displaystyle m_{x}=-2.5\log _{10}\left({\frac {F_{x}}{F_{x,0}}}\right),} where F x

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4056-458: The more noticeable asterisms in the sky. Following the three stars of Orion's belt in the direction opposite to Sirius , the first bright star encountered is Aldebaran. It is best seen at midnight between late November and early December. The star is, by chance, in the line of sight between the Earth and the Hyades , so it has the appearance of being the brightest member of the open cluster , but

4134-500: The naked eye. This can be useful as a way of monitoring the spread of light pollution . Apparent magnitude is technically a measure of illuminance , which can also be measured in photometric units such as lux . ( Vega , Canopus , Alpha Centauri , Arcturus ) The scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes . The brightest stars in

4212-439: The name aldebaranium (chemical symbol Ad) for a rare earth element that he (among others) had found. Today, it is called ytterbium (symbol Yb). Apparent visual magnitude Apparent magnitude ( m ) is a measure of the brightness of a star , astronomical object or other celestial objects like artificial satellites . Its value depends on its intrinsic luminosity , its distance, and any extinction of

4290-409: The night sky at visible wavelengths (and more at infrared wavelengths) as well as the bright planets Venus, Mars, and Jupiter, and since brighter means smaller magnitude, these must be described by negative magnitudes. For example, Sirius , the brightest star of the celestial sphere , has a magnitude of −1.4 in the visible. Negative magnitudes for other very bright astronomical objects can be found in

4368-406: The night sky were said to be of first magnitude ( m = 1), whereas the faintest were of sixth magnitude ( m = 6), which is the limit of human visual perception (without the aid of a telescope ). Each grade of magnitude was considered twice the brightness of the following grade (a logarithmic scale ), although that ratio was subjective as no photodetectors existed. This rather crude scale for

4446-444: The north. This, as well as observations of the changing positions of stars Sirius and Arcturus , led to the discovery of proper motion . Based on present day observations, the position of Aldebaran has shifted 7′ in the last 2000 years; roughly a quarter the diameter of the full moon . Due to precession of the equinoxes , 5,000 years ago the vernal equinox was close to Aldebaran. Between 420,000 and 210,000 years ago, Aldebaran

4524-408: The object's irradiance or power, respectively). The zero point of the apparent bolometric magnitude scale is based on the definition that an apparent bolometric magnitude of 0 mag is equivalent to a received irradiance of 2.518×10 watts per square metre (W·m ). While apparent magnitude is a measure of the brightness of an object as seen by a particular observer, absolute magnitude is a measure of

4602-445: The object's light caused by interstellar dust along the line of sight to the observer. Unless stated otherwise, the word magnitude in astronomy usually refers to a celestial object's apparent magnitude. The magnitude scale likely dates to before the ancient Roman astronomer Claudius Ptolemy , whose star catalog popularized the system by listing stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale

4680-570: The proper name Aldebaran for this star. Aldebaran is the brightest star in the constellation Taurus and so has the Bayer designation α Tauri, Latinised as Alpha Tauri. It has the Flamsteed designation 87 Tauri as the 87th star in the constellation of approximately 7th magnitude or brighter, ordered by right ascension . It also has the Bright Star Catalogue number 1457, the HD number 29139, and

4758-601: The radius of the star and has a temperature of about 1,500  K . The spectrum reveals lines of carbon monoxide , water , and titanium oxide . Outside the MOLSphere, the stellar wind continues to expand until it reaches the termination shock boundary with the hot, ionized interstellar medium that dominates the Local Bubble , forming a roughly spherical astrosphere with a radius of around 1000 au , centered on Aldebaran. Five faint stars appear close to Aldebaran in

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4836-429: The relative brightness measure in astrophotography to adjust exposure times between stars. Apparent magnitude also integrates over the entire object, regardless of its focus, and this needs to be taken into account when scaling exposure times for objects with significant apparent size, like the Sun, Moon and planets. For example, directly scaling the exposure time from the Moon to the Sun works because they are approximately

4914-469: The relative brightnesses of the blue supergiant Rigel and the red supergiant Betelgeuse irregular variable star (at maximum) are reversed compared to what human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light. Magnitudes obtained from this method are known as photographic magnitudes , and are now considered obsolete. For objects within the Milky Way with

4992-448: The residuals to the planet fit has determined that Aldebaran b has a minimum mass of 5.8 ± 0.7 Jupiter masses , and that when the star was on the main sequence it would have given this planet Earth-like levels of illumination and therefore, potentially, temperature. This would place it and any of its moons in the habitable zone . Follow-up study in 2019 have found the evidence for planetary existence inconclusive though. Aldebaran

5070-470: The same proper motion and parallax as Aldebaran and thus may be a physical binary system. These measurements are difficult, since the dim B component appears so close to the bright primary star, and the margin of error is too large to establish (or exclude) a physical relationship between the two. So far neither the B component, nor anything else, has been unambiguously shown to be physically associated with Aldebaran. The Gaia Data Release 3 again suggest

5148-429: The same size in the sky. However, scaling the exposure from the Moon to Saturn would result in an overexposure if the image of Saturn takes up a smaller area on your sensor than the Moon did (at the same magnification, or more generally, f/#). The dimmer an object appears, the higher the numerical value given to its magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Therefore,

5226-399: The sky. These double star components were given upper-case Latin letter designations more or less in the order of their discovery, with the letter A reserved for the primary star. Some characteristics of these components, including their position relative to Aldebaran, are shown in the table. Some surveys, for example Gaia Data Release 2 , have indicated that Alpha Tauri B may have about

5304-531: The sun around May 30 of each year. With a near- infrared J band magnitude of −2.1, only Betelgeuse (−2.9), R Doradus (−2.6), and Arcturus (−2.2) are brighter at that wavelength. On 11 March AD 509, a lunar occultation of Aldebaran was observed in Athens , Greece . English astronomer Edmund Halley studied the timing of this event, and in 1718 concluded that Aldebaran must have changed position since that time, moving several minutes of arc further to

5382-483: The system by defining a first magnitude star as a star that is 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today. This implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1 . This figure, the fifth root of 100 , became known as Pogson's Ratio. The 1884 Harvard Photometry and 1886 Potsdamer Duchmusterung star catalogs popularized Pogson's ratio, and eventually it became

5460-411: The variation is considered to be irregular. The photosphere shows abundances of carbon , oxygen , and nitrogen that suggest the giant has gone through its first dredge-up stage—a normal step in the evolution of a star into a red giant during which material from deep within the star is brought up to the surface by convection . With its slow rotation, Aldebaran lacks a dynamo needed to generate

5538-403: The wavelength of the light, and the way it varies depends on the type of light detector. For this reason, it is necessary to specify how the magnitude is measured for the value to be meaningful. For this purpose the UBV system is widely used, in which the magnitude is measured in three different wavelength bands: U (centred at about 350 nm, in the near ultraviolet ), B (about 435 nm, in

5616-468: Was diverging from Aldebaran, and hence they were not physically connected. However, the companion discovered by Burnham had almost exactly the same proper motion as Aldebaran, suggesting that the two formed a wide binary star system. Working at his private observatory in Tulse Hill , England , in 1864 William Huggins performed the first studies of the spectrum of Aldebaran, where he was able to identify

5694-464: Was made without metal parts, and used three miles of lashing. Hawaiʻiloa is 57 feet (17 m) long, with a beam of 19 feet (5.8 m). She has two sails, each of 240–420 square feet (22–39 m). She was initially launched in July 1993, and subsequently modified in dry dock before being re-launched a year later. In 1995, Hawaiʻiloa sailed her maiden voyage to Tahiti , Raʻiatea , and Nuku Hiva in

5772-425: Was mathematically defined to closely match this historical system by Norman Pogson in 1856. The scale is reverse logarithmic : the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to the brightness ratio of 100 5 {\displaystyle {\sqrt[{5}]{100}}} , or about 2.512. For example, a magnitude 2.0 star is 2.512 times as bright as

5850-489: Was not resolved in these observations. The extensive history of observations of Aldebaran led to it being included in the list of 33 stars chosen as benchmarks for the Gaia mission to calibrate derived stellar parameters. It had previously been used to calibrate instruments on board the Hubble Space Telescope . Aldebaran is listed as the spectral standard for type K5+ III stars . Its spectrum shows that it

5928-583: Was originally نَيِّر اَلدَّبَرَان ( Nayyir al-Dabarān in Arabic), meaning ' the bright one of the follower ' , since it follows the Pleiades; in fact, the Arabs sometimes also applied‍ the name al-Dabarān to the Hyades as a whole. A variety of transliterated spellings have been used, with the current Aldebaran becoming standard relatively recently. This easily seen and striking star in its suggestive asterism

6006-521: Was the brightest star in the night sky, peaking in brightness 320,000 years ago with an apparent magnitude of −1.54 . English astronomer William Herschel discovered a faint companion to Aldebaran in 1782; an 11th-magnitude star at an angular separation of 117 ″ . This star was shown to be itself a close double star by S. W. Burnham in 1888, and he discovered an additional 14th-magnitude companion at an angular separation of 31″. Follow-on measurements of proper motion showed that Herschel's companion

6084-399: Was visible from points in the northern hemisphere or close to the equator ; people in e.g. Australia or South Africa can never observe an Aldebaran occultation since it is too far south of the ecliptic. A reasonably accurate estimate for the diameter of Aldebaran was obtained during the occultation of 22 September 1978. In the 2020s, Aldebaran is in conjunction in ecliptic longitude with

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