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BL Herculis
BL Herculis is a variable star in the northern constellation of Hercules. Its apparent visual magnitude ranges from 9.70 to 10.62, so it is never bright enough to be seen with the naked eye, even with ideal observing conditions. Its distance from the Sun is about 3,850 light-years, and it is moving away from us at 18 km/sec. It is the prototype of the BL Herculis class of variable star, a short-period subset of the pulsating Cepheid variables. The variability of BL Herculis was discovered by Cuno Hoffmeister Cuno Hoffmeister (2 February 1892 – 2 January 1968) was a German astronomer, observer and discoverer of variable stars, comets and minor planets, and founder of Sonneberg Observatory. Born in Sonneberg in 1892 to Carl and Marie Hoffmeister, C ..., and announced in 1929. Early observations of the star produced a very inaccurate period of 4.2 days, which resulted in peculiar light and radial velocity curves. The first accurate period, 1.3 days, was published b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Curve
In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequency interval or band. Light curves can be periodic, as in the case of eclipsing binaries, Cepheid variables, other periodic variables, and transiting extrasolar planets, or aperiodic, like the light curve of a nova, a cataclysmic variable star, a supernova or a microlensing event or binary as observed during occultation events. The study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it. Variable stars Graphs of the apparent magnitude of a variable star over time are commonly used to visualise and analyse their behaviour. Although the categorisation of variable star types is increasingly done from their s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hipparcos
''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the first high-precision measurements of the intrinsic brightnesses (compared to the less precise apparent brightness), proper motions, and parallaxes of stars, enabling better calculations of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, astrophysicists were able to finally measure all six quantities needed to determine the motion of stars. The resulting ''Hipparcos Catalogue'', a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision ''Tycho Catalogue'' of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. ''Hipparcos' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythology, Roman mythological hero adapted from the Greek mythology, Greek hero Heracles. Hercules was one of the 48 constellations listed by the second-century astronomer Ptolemy, and it remains one of the IAU designated constellations, 88 modern constellations today. It is the fifth-largest of the modern constellations and is the largest of List of brightest stars, the 50 which have no stars brighter than apparent Magnitude (astronomy), magnitude +2.5. Characteristics Hercules is bordered by Draco (constellation), Draco to the north; Boötes, Corona Borealis, and Serpens, Serpens Caput to the east; Ophiuchus to the south; Aquila (constellation), Aquila to the southwest; and Sagitta, Vulpecula, and Lyra to the west. Covering 1225.1 square degrees and 2.970% of the night sky, it ranks fifth among the 88 constellations in size. The three-letter abbreviation for the constellation, as adopted by the International Astro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BL Herculis Variable
BL Herculis variables are a subclass of type II Cepheids with low luminosity and mass, that have a period of less than eight days. They are pulsating stars with light curves that frequently show a bump on the descending side for stars of the shortest periods and on the ascending side for longer period stars. Like other type II Cepheids, they are very old population II stars found in the galaxy’s halo and globular clusters. Also, compared to other type II Cepheids, BL Herculis variables have shorter periods and are fainter than W Virginis variables. Pulsating stars vary in spectral class as they vary in brightness and BL Herculis variables are normally class A at their brightest and class F when most dim. When plotted on the Hertzsprung–Russell diagram they fall in-between W Virginis and RR Lyrae variables. The prototype star, BL Herculis, varies between magnitude 9.7 and 10.6 in a period of 1.3 days. The brightest BL Herculis variables, with their maximum magnitudes, are: * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Variable Star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: * Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks. * Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it. Many, possibly most, stars have at least some variation in luminosity: the energy output of the Sun, for example, varies by about 0.1% over an 11-year solar cycle. Discovery An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. Of the modern astronomers, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellations likely go back to prehistory. People used them to relate stories of their beliefs, experiences, creation myth, creation, or mythology. Different cultures and countries adopted their own constellations, some of which lasted into the early 20th century before today's constellations were internationally recognized. The recognition of constellations has changed significantly over time. Many changed in size or shape. Some became popular, only to drop into obscurity. Some were limited to a single culture or nation. The 48 traditional Western constellations are Greek. They are given in Aratus' work ''Phenomena'' and Ptolemy's ''Almagest'', though their origin probably predates these works by several centuries. Constellation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apparent Magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer. The word ''magnitude'' in astronomy, unless stated otherwise, usually refers to a celestial object's apparent magnitude. The magnitude scale dates back to the ancient Roman astronomer Claudius Ptolemy, whose star catalog listed stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined in a way to closely match this historical system. The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to a brightness ratio of \sqrt /math>, or about 2.512. For example, a star of magnitude 2.0 is 2.512 times as bright as a star of magnitude 3.0, 6. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 (one million million, or billion in long scale). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one Julian year (365.25 days). Because it includes the time-measurement word "year", the term ''light-year'' is sometimes misinterpreted as a unit of time. The ''light-year'' is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist contexts and popular science publications. The unit most commonly used in professional astronomy is the parsec (symbol: pc, about 3.26 light-years) which derives from astrometry; it is the distance at which one astronomical unit subtends an angle of one second of arc. Defini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cepheid Variable
A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid variable's luminosity and pulsation period established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances. This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period. This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness. The term ''Cepheid'' originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified. The mechanics of stellar pu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cuno Hoffmeister
Cuno Hoffmeister (2 February 1892 – 2 January 1968) was a German astronomer, observer and discoverer of variable stars, comets and minor planets, and founder of Sonneberg Observatory. Born in Sonneberg in 1892 to Carl and Marie Hoffmeister, Cuno Hoffmeister obtained his first telescope in 1905 and became an avid amateur astronomer. After his father lost most of his money in 1914, Hoffmeister had to leave school in 1916 to start an apprenticeship in his father's company. During this time he continued to study spherical mathematics and trigonometry. In April 1915 he had the opportunity to substitute as the assistant of Ernst Hartwig at ''Remeis Observatory'' in Bamberg while the current holder of the position was drafted, mainly working on observations of meteors and variable stars. He held this position until the end of the war and then moved back to Sonneberg, where he made his Abitur in 1920. After studying at the University of Jena, while at the same time continuing to work i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pavel Petrovich Parenago
Pavel Petrovich Parenago (20 March 1906 – 5 January 1960) was a Soviet scientist, astronomer, and professor. He served as the head of the Department of Stellar Astronomy at M.V. Lomonosov Moscow State University and a Corresponding Member of the Soviet Academy of Sciences. Early life and education Pavel Petrovich Parenago was born into the family of a physician on 20 March 1906, in Krasnodar, present-day Russia. He completed his middle school education in Moscow in 1922, having begun scientific work while still in senior classes. He went on to graduate from Moscow State University in 1929 as a trained and qualified scientist. Research In 1932, Parenago began studies of the structure and kinematics of the Milky Way based primarily on star data. He and a colleague, B.V. Kukarkin, began an extensive compilation of variable star data. During his studies, Parenago observed approximately 3,000 stars in the Orion nebula region of the galaxy, the nearest star creating region to the Su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
