In physics, redshift is a phenomenon where electromagnetic radiation from an object undergoes an increase in wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave frequency and photon energy, in accordance with the wave and quantum theories of light. Neither the emitted nor perceived light is red. Examples of redshifting are a gamma ray perceived as an X-ray, or visible light perceived as radio waves; the opposite of a redshift is energy increases. However, redshift is a more common term and sometimes blueshift is referred to as negative redshift. There are three main causes of red in astronomy and cosmology: Objects move apart in space; this is an example of the Doppler effect. Space itself expands; this is known as cosmological redshift. All sufficiently distant light sources show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles.
Knowledge of redshifts and blueshifts has been used to develop several terrestrial technologies such as Doppler radar and radar guns. Redshifts are seen in the spectroscopic observations of astronomical objects, its value is represented by the letter z. A special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity. Special relativistic and cosmological redshifts can be understood under the umbrella of frame transformation laws. There exist other physical processes that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842.
The hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler predicted that the phenomenon should apply to all waves, in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth. Before this was verified, however, it was found that stellar colors were due to a star's temperature, not motion. Only was Doppler vindicated by verified redshift observations; the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is sometimes called the "Doppler–Fizeau effect". In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, the yearly change in the Doppler shift of stars located near the ecliptic due to the orbital velocity of the Earth.
In 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The earliest occurrence of the term red-shift in print appears to be by American astronomer Walter S. Adams in 1908, in which he mentions "Two methods of investigating that nature of the nebular red-shift"; the word does not appear unhyphenated until about 1934 by Willem de Sitter indicating that up to that point its German equivalent, was more used. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies mostly thought to be spiral nebulae, had considerable redshifts. Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years he wrote a review in the journal Popular Astronomy. In it he states that "the early discovery that the great Andromeda spiral had the quite exceptional velocity of –300 km showed the means available, capable of investigating not only the spectra of the spirals but their velocities as well."
Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable "positive" velocities. Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such "nebulae" and the distances to them with the formulation of his eponymous Hubble's law; these observations corroborated Alexander Friedmann's 1922 work, in which he derived the Friedmann-Lemaître equations. They are today considered strong evidence for the Big Bang theory; the spectrum of light that comes from a single source can be measured. To determine the redshift, one searches for features in the spectrum such as absorption lines, emission lines, or other variations in light intensity. If found, these featur
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines; each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary due to the temperature of the photosphere, although in some cases there are true abundance differences; the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are classified under the Morgan-Keenan system using the letters O, B, A, F, G, K, M, a sequence from the hottest to the coolest; each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and classes S and C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd for sub-dwarfs, class D for white dwarfs; the full spectral class for the Sun is G2V, indicating a main-sequence star with a temperature around 5,800 K. The conventional color description takes into account only the peak of the stellar spectrum. In actuality, stars radiate in all parts of the spectrum; because all spectral colors combined appear white, the actual apparent colors the human eye would observe are far lighter than the conventional color descriptions would suggest. This characteristic of'lightness' indicates that the simplified assignment of colors within the spectrum can be misleading.
Excluding color-contrast illusions in dim light, there are indigo, or violet stars. Red dwarfs are a deep shade of orange, brown dwarfs do not appear brown, but hypothetically would appear dim grey to a nearby observer; the modern classification system is known as the Morgan–Keenan classification. Each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the star's spectral type. Other modern stellar classification systems, such as the UBV system, are based on color indexes—the measured differences in three or more color magnitudes; those numbers are given labels such as "U-V" or "B-V", which represent the colors passed by two standard filters. The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon, who re-ordered and simplified a prior alphabetical system. Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions.
Main-sequence stars vary in surface temperature from 2,000 to 50,000 K, whereas more-evolved stars can have temperatures above 100,000 K. Physically, the classes indicate the temperature of the star's atmosphere and are listed from hottest to coldest; the spectral classes O through M, as well as other more specialized classes discussed are subdivided by Arabic numerals, where 0 denotes the hottest stars of a given class. For example, A0 denotes A9 denotes the coolest ones. Fractional numbers are allowed; the Sun is classified as G2. Conventional color descriptions are traditional in astronomy, represent colors relative to the mean color of an A class star, considered to be white; the apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, appear white or bluish white to the unaided eye because they are too dim for color vision to work. Red supergiants are cooler and redder than dwarfs of the same spectral type, stars with particular spectral features such as carbon stars may be far redder than any black body.
The fact that the Harvard classification of a star indicated its surface or photospheric temperature was not understood until after its development, though by the time the first Hertzsprung–Russell diagram was formulated, this was suspected to be true. In the 1920s, the Indian physicist Meghnad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First he applied it to the solar chromosphere to stellar spectra. Harvard astronomer Cecilia Payne demonstrated that the O-B-A-F-G-K-M spectral sequence is a sequence in temperature; because the classification sequence predates our understanding that it is a temperature sequence, the placement of a spectrum into a given subtype, such as B3 or A7, depends upon estimates of the strengths of absorption features in stellar spectra. As a result, these subtypes are not evenly divided into any sort of mathematically representable intervals; the Yerkes spectral classification called the MKK system from the authors' initial
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, its symbol is ♍. Lying between Leo to the west and Libra to the east, it is the second-largest constellation in the sky and the largest constellation in the zodiac, it can be found through its brightest star, Spica. The bright star Spica makes it easy to locate Virgo, as it can be found by following the curve of the Big Dipper/Plough to Arcturus in Boötes and continuing from there in the same curve. Due to the effects of precession, the First Point of Libra, lies within the boundaries of Virgo close to β Virginis; this is one of the two points in the sky where the celestial equator crosses the ecliptic This point will pass into the neighbouring constellation of Leo around the year 2440. Besides Spica, other bright stars in Virgo include β Virginis, γ Virginis, δ Virginis and ε Virginis. Other fainter stars that were given names are ζ Virginis, η Virginis, ι Virginis, κ Virginis, λ Virginis and φ Virginis; the star 70 Virginis has one of the first known extrasolar planetary systems with one confirmed planet 7.5 times the mass of Jupiter.
The star Chi Virginis has one of the most massive planets detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets: one is a super-Earth and two are Neptune-mass planets. SS Virginis is a variable star with a noticeable red color, it varies in magnitude from a minimum of 9.6 to a maximum of 6.0 over a period of one year. There are 35 verified exoplanets orbiting 29 stars in Virgo, including PSR B1257+12, 70 Virginis, Chi Virginis, 61 Virginis, NY Virginis, 59 Virginis; because of the presence of a galaxy cluster within its borders 5° to 12° west of ε Vir, this constellation is rich in galaxies. Some examples are Messier 49, Messier 58, Messier 59, Messier 60, Messier 61, Messier 84, Messier 86, Messier 87, Messier 89 and Messier 90. A noted galaxy, not part of the cluster is the Sombrero Galaxy, an unusual spiral galaxy, it is located about 10° due west of Spica. NGC 4639 is a face-on barred spiral galaxy located 78 Mly from Earth, its outer arms have a high number of Cepheid variables, which are used as standard candles to determine astronomical distances.
Because of this, astronomers used several Cepheid variables in NGC 4639 to calibrate type 1a supernovae as standard candles for more distant galaxies. Virgo possesses several galaxy clusters, one of, HCG 62. A Hickson Compact Group, HCG 62 is at a distance of 200 Mly from Earth and possesses a large central elliptical galaxy, it has a heterogeneous halo of hot gas, posited to be due to the active galactic nucleus at the core of the central elliptical galaxy. M87 is the largest galaxy in the Virgo cluster, is at a distance of 60 Mly from Earth, it is a major radio source due to its jet of electrons being flung out of the galaxy by its central supermassive black hole. Because this jet is visible in several different wavelengths, it is of interest to astronomers who wish to observe black holes in a unique galaxy. M84 is another elliptical radio galaxy in the constellation of Virgo. Astronomers have surmised that the speed of the gas clouds orbiting the core indicates the presence of an object with a mass 300 million times that of the sun, most a black hole.
The Sombrero Galaxy, M104, is an edge-on spiral galaxy located 28 million light-years from Earth. It has a bulge at its center made up of older stars, larger than normal, it is surrounded by large, bright globular clusters and has a prominent dust lane made up of polycyclic aromatic hydrocarbons. NGC 4438 is a peculiar galaxy with an active galactic nucleus, at a distance of 50 Mly from Earth, its supermassive black hole is ejecting jets of matter, creating bubbles with a diameter of up to 78 ly. NGC 4261 has a black hole 20 ly from its center with a mass of 1.2 billion solar masses. It is located at a distance of 45 Mly from Earth, has an unusually dusty disk with a diameter of 300 ly. Along with M84 and M87, NGC 4261 has strong emissions in the radio spectrum. IC 1101 is a supergiant elliptical galaxy in the Abell 2029 galaxy cluster located about 1.07 Gly from Earth. At the diameter of 5.5 million light years, or more than 50 times the size of the Milky Way, it was the largest known galaxy in the universe.
Virgo is home to the quasar 3C 273, the first quasar to be identified. With a magnitude of ~12.9 it is the optically brightest quasar in the sky. In the Babylonian MUL. APIN, part of this constellation was known as "The Furrow", representing the goddess Shala and her ear of grain. One star in this constellation, retains this tradition as it is Latin for "ear of grain", one of the major products of the Mesopotamian furrow. For this reason the constellation became associated with fertility; the constellation of Virgo in Hipparchus corresponds to two Babylonian constellations: the "Furrow" in the eastern sector of Virgo and the "Frond of Erua" in the western sector. The Frond of Erua was depicted as a godde
Leuschner Observatory called the Students' Observatory, is an observatory jointly operated by the University of California and San Francisco State University. The observatory was built in 1886 on the Berkeley campus. For many years, it was directed by Armin Otto Leuschner, for whom the observatory was renamed in 1951. In 1965, it was relocated to its present home in Lafayette, California 10 miles east of the Berkeley campus. In 2012, the physics and astronomy department of San Francisco State University became a partner. Presently, Leuschner Observatory has two operating telescopes. One is a 30-inch optical telescope, equipped with a CCD for observations in visible light and an infrared detector used for infrared astronomy; the other is a 12-foot radio dish used for an undergraduate radio astronomy course. The observatory has been used to perform professional astronomy research, such as orbit determination of small solar system bodies in the early 1900s and supernova surveys in the 1980s and 1990s.
It has served as a primary tool in the education of graduate and undergraduate students at UC Berkeley. The Students' Observatory was constructed in 1886 on the Berkeley campus, with the original funds provided by the California legislature in order for the observatory to provide practical training to civil engineers; the Students' Observatory became seen as a training ground for students studying astronomy, so that they would be better prepared to go on to use the facilities at Lick Observatory. This contributed to the separation of the departments of civil engineering and astronomy in the mid-1890s, with the Students' Observatory becoming the home of the Berkeley Astronomy Department. In 1898, Armin Otto Leuschner was appointed the director of the Students' Observatory, a post that he held until his retirement in 1938. During this time, "the observatory became a center for the computation of the orbits of comets, minor planets, satellites." Astronomer Simon Newcomb said that Leuschner organized the department and observatory into "a thorough school of astronomy, than which there is none better."
After he stepped down, the observatory was directed by a series of well regarded astronomers, including Otto Struve from 1950–59 and Louis G. Henyey from 1959–64; the Students' Observatory was renamed Leuschner Observatory by the Regents of the University of California in 1951 in honor of A. O. Leuschner; the Space Sciences Lab, which operates SETI, began operations in 1960 at Leuschner Observatory until a permanent home in the Berkeley hills was completed in 1966. In 1965, the observatory was relocated a short distance east of the Berkeley campus in the hills of Lafayette, California, on the 283-acre Russell Reservation. In 1968, the observatory was equipped with a new 30-inch Ritchey-Chretien telescope built by Tinsley Laboratories. Since, the observatory has been used as a testing ground for a variety of experiments and instruments; the predecessor to the Katzman Automatic Imaging Telescope was tested at Leuschner Observatory in the early 1990s, in the early 2000s, the first prototype of the telescopes used at the Allen Telescope Array was unveiled at Leuschner.
Leuschner Observatory's 30-inch telescope continues to be used in undergraduate astronomical instruction, while the 20-inch telescope was decommissioned and is in disrepair. In 2012, the physics and astronomy department of San Francisco State University bought into the 30-inch telescope. SF State and UC Berkeley staff jointly refurbished and upgraded the motors and control system of the larger telescope. Leuschner Observatory houses two optical telescopes, one with a 30-inch diameter and the other with a 20-inch diameter; as of 2010, the 20-inch telescope is not usable, the 30-inch telescope is undergoing upgrades. The 30-inch telescope is of Ritchey-Chretien design, is equipped with both a charge coupled device for observations in visible light and an infrared detector, fabricated in 2000 in order to create an infrared laboratory course for undergraduate students at UC Berkeley. Both optical telescopes are outfitted with control systems which allow them be automated, meaning observations are made with minimal human intervention.
Leuschner Observatory is home to a single 3.6-metre radio telescope. The telescope was one of the prototypes for the Allen Telescope Array that were tested at Leuschner, has since been used in the undergraduate radio astronomy lab; the telescope operates between 1320–1740 MHz and uses an 8192 element spectrometer with spectral resolution of about 1.5 kHz and a 12 MHz bandwidth. The operating range allows for it to be used to observe the 21-cm hydrogen line as well as hydroxyl lines from astrophysical masers. Research at the Students' Observatory under A. O. Leuschner was focused on performing astrometry in order to determine orbits for newly discovered comets; when Clyde Tombaugh reported the discovery of Pluto in 1930, Leuschner began observing it using the instruments at Students' Observatory to determine its orbit. Within months of its discovery, Leuschner cast the first doubt on Pluto's status as a planet, suggesting instead that it was unclear whether Pluto was a large asteroid, a planet, or a comet.
Using a few weeks of observation at the Students' Observatory, he and his students Fred Whipple and E. C. Bower determined an upper limit of one half the mass of Earth; this mass meant Pluto was insufficiently massive to be the Planet X thought to cause discrepancies between the predicted and observed orbit of Neptune. The observatory was fo
Type Ia supernova
A type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an smaller white dwarf. Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses. Beyond this, they in some cases trigger a supernova explosion. Somewhat confusingly, this limit is referred to as the Chandrasekhar mass, despite being marginally different from the absolute Chandrasekhar limit where electron degeneracy pressure is unable to prevent catastrophic collapse. If a white dwarf accretes mass from a binary companion, the general hypothesis is that its core will reach the ignition temperature for carbon fusion as it approaches the limit. However, if the white dwarf merges with another white dwarf, it will momentarily exceed the limit and begin to collapse, again raising its temperature past the nuclear fusion ignition point. Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy to unbind the star in a supernova explosion.
This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends on the distance. In May 2015, NASA reported that the Kepler space observatory observed KSN 2011b, a type Ia supernova in the process of exploding. Details of the pre-nova moments may help scientists better judge the quality of Type Ia supernovae as standard candles, an important link in the argument for dark energy; the Type Ia supernova is a subcategory in the Minkowski–Zwicky supernova classification scheme, devised by German-American astronomer Rudolph Minkowski and Swiss astronomer Fritz Zwicky. There are several means by which a supernova of this type can form, but they share a common underlying mechanism. Theoretical astronomers long believed the progenitor star for this type of supernova is a white dwarf, empirical evidence for this was found in 2014 when a Type Ia supernova was observed in the galaxy Messier 82.
When a slowly-rotating carbon–oxygen white dwarf accretes matter from a companion, it can exceed the Chandrasekhar limit of about 1.44 M☉, beyond which it can no longer support its weight with electron degeneracy pressure. In the absence of a countervailing process, the white dwarf would collapse to form a neutron star, in an accretion-induced non-ejective process, as occurs in the case of a white dwarf, composed of magnesium and oxygen; the current view among astronomers who model Type Ia supernova explosions, however, is that this limit is never attained and collapse is never initiated. Instead, the increase in pressure and density due to the increasing weight raises the temperature of the core, as the white dwarf approaches about 99% of the limit, a period of convection ensues, lasting 1,000 years. At some point in this simmering phase, a deflagration flame front is powered by carbon fusion; the details of the ignition are still unknown, including the location and number of points where the flame begins.
Oxygen fusion is initiated shortly thereafter, but this fuel is not consumed as as carbon. Once fusion begins, the temperature of the white dwarf increases. A main sequence star supported by thermal pressure can expand and cool which automatically regulates the increase in thermal energy. However, degeneracy pressure is independent of temperature; the flare accelerates in part due to the Rayleigh–Taylor instability and interactions with turbulence. It is still a matter of considerable debate whether this flare transforms into a supersonic detonation from a subsonic deflagration. Regardless of the exact details of how the supernova ignites, it is accepted that a substantial fraction of the carbon and oxygen in the white dwarf fuses into heavier elements within a period of only a few seconds, with the accompanying release of energy increasing the internal temperature to billions of degrees; the energy released is more than sufficient to unbind the star. The star explodes violently and releases a shock wave in which matter is ejected at speeds on the order of 5,000–20,000 km/s 6% of the speed of light.
The energy released in the explosion causes an extreme increase in luminosity. The typical visual absolute magnitude of Type Ia supernovae is Mv = −19.3, with little variation. The theory of this type of supernova is similar to that of novae, in which a white dwarf accretes matter more and does not approach the Chandrasekhar limit. In the case of a nova, the infalling matter causes a hydrogen fusion surface explosion that does not disrupt the star. Type Ia supernova differ from Type II supernova, which are caused by the cataclysmic explosion of the outer layers of a massive star as its core collapses, powered by release of gravitational potential energy via neutrino emission. One model for the formation of this category of supernova is a close binary star system; the progenitor binary system consists of main sequence stars, with the primary possessing more mass than the secondary. Being greater in mass, the prima
Alexei Vladimir "Alex" Filippenko is an American astrophysicist and professor of astronomy at the University of California, Berkeley. Filippenko graduated from Dos Pueblos High School in California, he received a Bachelor of Arts in physics from the University of California, Santa Barbara in 1979 and a Ph. D. in astronomy from the California Institute of Technology in 1984, where he was a Hertz Foundation Fellow. He was a Miller Fellow at UC Berkeley and was subsequently appointed to a faculty position at the same institution, he was named a Miller Research Professor for Spring 1996 and Spring 2005. His research focuses on supernovae and active galaxies at optical and near-infrared wavelengths. Filippenko is the only person, a member of both the Supernova Cosmology Project and the High-z Supernova Search Team, which used observations of extragalactic supernovae to discover the accelerating universe and its implied existence of dark energy; the discovery was voted the top science breakthrough of 1998 by Science magazine and resulted in the 2011 Nobel prize for physics being awarded to the leaders of the two project teams.
Filippenko developed and runs the Katzman Automatic Imaging Telescope, a robotic telescope which conducts the Lick Observatory Supernova Search, the most successful nearby supernova search. He is a member of the Nuker Team which uses the Hubble space telescope to examine supermassive black holes and determined the relationship between a galaxy's central black hole's mass and velocity dispersion; the Thompson-Reuters "incites" index ranked Filippenko as the most cited researcher in space science for the ten-year period between 1996 and 2006. Filippenko is featured in the History Channel series The Universe. Filippenko is the author of and teacher in an eight-volume teaching series on DVD called Understanding the Universe. Organized into three major sections in ten smaller units, this series of 96 half-hour lectures covers the material of an undergraduate survey course for An Introduction to Astronomy. With co-author Jay M. Pasachoff, Filippenko wrote the award-winning introductory textbook The Cosmos: Astronomy in the New Millennium.
Filippenko was awarded the Newton Lacy Pierce Prize in Astronomy in 1992 and a Guggenheim Fellowship in 2000. In 1997, the Canadian Astronomical Society invited him to give the Robert M. Petrie Prize Lecture for his significant contributions to astrophysical research, he was invited to give the 42nd Oppenheimer Memorial Lecture in 2012. He was recognized in the 2007 Gruber Cosmology Prize for his work with Miller Postdoctoral Fellow Adam G. Riess and for his specialized contributions in measurement of the apparent brightness of distant supernovae, which established the distances that support the conclusion of an rapid expansion of the universe. Filippenko was elected to the National Academy of Sciences in 2009, he shared the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt, Adam Riess, the High-Z Supernova Search Team. In addition to recognition for his scholarship, he has received numerous honors for his undergraduate teaching, including the 2007 Richtmyer Memorial Award given annually by the American Association of Physics Teachers and the Carl Sagan Prize for Science Popularization by Wonderfest in 2004.
In 2006 Filippenko was awarded the US Professor of the Year Award, sponsored by The Carnegie Foundation for the Advancement of Teaching and administered by the Council for Advancement and Support of Education. He won the 2010 Richard H. Emmons Award for excellence in college astronomy teaching, issued by the Astronomical Society of the Pacific, his teaching awards at UC Berkeley include the Donald S. Noyce Prize for Excellence in Undergraduate Teaching in the Physical Sciences and the Distinguished Teaching Award; the UC Berkeley student body has voted him nine times as their "Best Professor" on campus. Filippenko is married to Noelle Filippenko and has four children, Simon and Orion. UC Berkeley Astronomy biography UC Berkeley Astronomy website Alex Filippenko on IMDb Introduction to General Astronomy – UC Berkeley Webcast Dark Energy and the Runaway Universe – UC Berkeley Webcast
A constellation is a group of stars that forms an imaginary outline or pattern on the celestial sphere representing an animal, mythological person or creature, a god, or an inanimate object. The origins of the earliest constellations go back to prehistory. People used them to relate stories of their beliefs, 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. Adoption of constellations has changed over time. Many have changed in shape; some became popular. Others were limited to single nations; the 48 traditional Western constellations are Greek. They are given in Aratus' work Phenomena and Ptolemy's Almagest, though their origin predates these works by several centuries. Constellations in the far southern sky were added from the 15th century until the mid-18th century when European explorers began traveling to the Southern Hemisphere. Twelve ancient constellations belong to the zodiac.
The origins of the zodiac remain uncertain. In 1928, the International Astronomical Union formally accepted 88 modern constellations, with contiguous boundaries that together cover the entire celestial sphere. Any given point in a celestial coordinate system lies in one of the modern constellations; some astronomical naming systems include the constellation where a given celestial object is found to convey its approximate location in the sky. The Flamsteed designation of a star, for example, consists of a number and the genitive form of the constellation name. Other star patterns or groups called asterisms are not constellations per se but are used by observers to navigate the night sky. Examples of bright asterisms include the Pleiades and Hyades within the constellation Taurus or Venus' Mirror in the constellation of Orion.. Some asterisms, like the False Cross, are split between two constellations; the word "constellation" comes from the Late Latin term cōnstellātiō, which can be translated as "set of stars".
The Ancient Greek word for constellation is ἄστρον. A more modern astronomical sense of the term "constellation" is as a recognisable pattern of stars whose appearance is associated with mythological characters or creatures, or earthbound animals, or objects, it can specifically denote the recognized 88 named constellations used today. Colloquial usage does not draw a sharp distinction between "constellations" and smaller "asterisms", yet the modern accepted astronomical constellations employ such a distinction. E.g. the Pleiades and the Hyades are both asterisms, each lies within the boundaries of the constellation of Taurus. Another example is the northern asterism known as the Big Dipper or the Plough, composed of the seven brightest stars within the area of the IAU-defined constellation of Ursa Major; the southern False Cross asterism includes portions of the constellations Carina and Vela and the Summer Triangle.. A constellation, viewed from a particular latitude on Earth, that never sets below the horizon is termed circumpolar.
From the North Pole or South Pole, all constellations south or north of the celestial equator are circumpolar. Depending on the definition, equatorial constellations may include those that lie between declinations 45° north and 45° south, or those that pass through the declination range of the ecliptic or zodiac ranging between 23½° north, the celestial equator, 23½° south. Although stars in constellations appear near each other in the sky, they lie at a variety of distances away from the Earth. Since stars have their own independent motions, all constellations will change over time. After tens to hundreds of thousands of years, familiar outlines will become unrecognizable. Astronomers can predict the past or future constellation outlines by measuring individual stars' common proper motions or cpm by accurate astrometry and their radial velocities by astronomical spectroscopy; the earliest evidence for the humankind's identification of constellations comes from Mesopotamian inscribed stones and clay writing tablets that date back to 3000 BC.
It seems that the bulk of the Mesopotamian constellations were created within a short interval from around 1300 to 1000 BC. Mesopotamian constellations appeared in many of the classical Greek constellations; the oldest Babylonian star catalogues of stars and constellations date back to the beginning in the Middle Bronze Age, most notably the Three Stars Each texts and the MUL. APIN, an expanded and revised version based on more accurate observation from around 1000 BC. However, the numerous Sumerian names in these catalogues suggest that they built on older, but otherwise unattested, Sumerian traditions of the Early Bronze Age; the classical Zodiac is a revision of Neo-Babylonian constellations from the 6th century BC. The Greeks adopted the Babylonian constellations in the 4th century BC. Twenty Ptolemaic constellations are from the Ancient Near East. Another ten have the same stars but different names. Biblical scholar, E. W. Bullinger interpreted some of the creatures mentioned in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac, with the Lion as Leo, the Bull as Taurus, the Man representing Aquarius and the Eagle standing in for Scorpio.
The biblical Book of Job also