Robot series (Asimov)
The Robot series is a series of 38 science fiction short stories and five novels by American writer Isaac Asimov, featuring positronic robots. Most of Asimov's robot short stories, which he began to write in 1939, are set in the first age of positronic robotics and space exploration; the unique feature of Asimov's robots are the Three Laws of Robotics, hardwired in a robot's positronic brain, with which all robots in his fiction must comply, which ensure that the robot does not turn against its creators. The stories were not conceived as a set, but rather all feature his positronic robots—indeed, there are some inconsistencies among them between the short stories and the novels, they all share a theme of the interaction of humans and morality. Some of the short stories found in The Complete Robot and other anthologies appear not to be set in the same universe as the Foundation Universe. "Victory Unintentional" has positronic robots obeying the Three Laws, but a non-human civilization on Jupiter.
"Let's Get Together" features humanoid robots, but from a different future, with no mention of the Three Laws. The multiple series offers a sense of completeness, because all of its works are interconnected in some way; the first book is I, Robot, a collection of nine published short stories woven together as a 21st-century interview with robopsychologist Dr. Susan Calvin; the next four robot novels The Caves of Steel, The Naked Sun, The Robots of Dawn, Robots and Empire make up the Elijah Baley series, are mysteries starring the Terran Elijah Baley and his humaniform robot partner, R. Daneel Olivaw, they are set thousands of years after the short stories and focus on the conflicts between Spacers — descendants of human settlers from other planets — and the people from an overcrowded Earth. "Mirror Image", one of the short stories from The Complete Robot anthology, is set in this time period and features both Baley and Olivaw. Another short story, "Mother Earth", is set about a thousand years before the robot novels, when the Spacer worlds chose to become separated from Earth.
The Caves of Steel and The Naked Sun are both considered classics of the genre, but the novels were well received, with The Robots of Dawn nominated for both the Hugo and Locus Awards in 1984, Robots and Empire shortlisted for the Locus Award for Best Science Fiction Novel in 1986. One source of inspiration for Asimov's robots was the Zoromes, a race of mechanical men that featured in a 1931 short story called "The Jameson Satellite", by Neil R. Jones. Asimov read this story at the age of 11, acknowledged it as a source of inspiration in Before the Golden Age, an anthology of 1930s science fiction in which Asimov told the story of the science fiction he read during his formative years. In Asimov's own words: It is from the Zoromes, beginning with their first appearance in "The Jameson Satellite," that I got my own feeling for benevolent robots who could serve man with decency, as these had served Professor Jameson, it was the Zoromes who were the spiritual ancestors of my own "positronic robots," all of them, from Robbie to R. Daneel.
Asimov integrated the Robot Series into his all-encompassing Foundation series, making R. Daneel Olivaw appear again twenty thousand years in the age of the Galactic Empire, in sequels and prequels to the original Foundation trilogy; the Stars, Like Dust states explicitly. Asimov explained that the in-universe reason for this perception was that it was formulated by Earthmen many centuries after the event, which had become distorted, due to the loss of much of their planetary history; this work is regarded as part of the Empire series, but does not directly mention either Trantor or the Spacer worlds. One character is seen with a visi-sonor, the same musical instrument, played by the clown Magnifico in Foundation and Empire. Based on details from the novel, such as Earth still being habitable and the absence of a unified galactic government, it would fall during the early formation of the Empire; the 1989 anthology Foundation's Friends included the positronic robot stories "Balance" by Mike Resnick, "Blot" by Hal Clement, "PAPPI" by Sheila Finch, "Plato's Cave" by Poul Anderson, "The Fourth Law of Robotics" by Harry Harrison and "Carhunters of the Concrete Prairie" by Robert Sheckley.
Not all of these stories are consistent with the Asimov stories. The anthology included "Strip-Runner" by Pamela Sargent, set in the era of the Elijah Baley novels. Shortly before his death in 1992, Asimov approved an outline for three novels by Roger MacBride Allen, set between Robots and Empire and the Empire series, telling the story of the terraforming of the Spacer world Inferno, about the robot revolution started by creating a "No Law" Robot, New Law Robots. There is another set of novels by various authors, loosely connected to the Robots Series, but containing many inconsistencies with Asimov's books, which are not considered canon; the Asimov estate authorized publication of another trilogy of robot mysteries by Mark W. Tiedemann; these novels, which take place several years before Asimov's Robots and Empire, are Mirage (20
Foundation's Triumph is a science fiction novel by David Brin, set in Isaac Asimov's Foundation universe. It is the third book of the Second Foundation trilogy, written after Asimov's death by three authors, authorized by the Asimov estate. Brin synthesizes dozens of Foundation-Empire-Robots novels and short stories by Isaac Asimov, Roger MacBride Allen, authorized others into a consistent framework. Foundation's Triumph includes an appendix chronology compiled by Attila Torkos. Foundation’s Triumph starts with Hari Seldon who reviews his life and has to accept the fact that his “purpose” is completed. One day he meets a bureaucrat, Horis Antic, who explains his theory about the correlation of certain soils on planets and psychohistory. Seldon agrees to take a trip to some of the planets. Hari and Horis travel to Demarchia. Parallel to Seldon’s story, Dors Venabili starts out on the planet Panucopia to meet Lodovik Trema, a robot whose Three Laws of Robotics have been erased. Lodovic gives her the head of R. Giskard Reventlov, an important robot who founded the Zeroth Law with R. Daneel Olivaw.
She finds out that Daneel never consulted a human while founding the Zeroth Law. Trema meets a faction of cyborgs and joins them. After Dors has become a rebel, she fights for the cyborgs as well; the third plot of the novel is on Eos. Daneel talks to his possible successor Zun Lurrin. All chapters with Olivaw as the main character are written in a different typeface. In Seldon's story, during the flight to the first planet the yacht is taken over by rebels, who are from the renaissance or chaos planet Ktlina, they show Seldon ancient spaceships with many data capsules from the human past. Robots take over the yacht and destroy the data capsules and the ancient ships with the permission of Seldon. During the flight back to Trantor, a rebel, Gornon Vlimt, turns out to be another robot from a faction of Calvinians, who want to send Hari into the future. At last all factions meet on Earth; the Calvinians are stopped by Wanda Seldon. Old friends Seldon and Daneel meet one final time. Despite the apparent eventual dominance of Galaxia, Seldon confides his belief that the second Galactic Empire will include both the two Foundations, following the Seldon Plan, Galaxia.
"Will there be an Encyclopedia Galactica a thousand years from now," asks Seldon, betting that if his belief is correct, there will be updated editions of it. Since most Foundation novels use the Encyclopedia as a framing device for its chapters, this implies that Seldon predicted the successful synthesis of the two Foundations and Galaxia. Brin stated in his book that he could well imagine to write a sequel to Foundation's Triumph, or that another author might, he refrained from giving any details on what was on his mind, but noted that he might release a rough start one day, which he did on his website, titled "Denouement"
Science fiction is a genre of speculative fiction dealing with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, extraterrestrials in fiction. Science fiction explores the potential consequences of scientific other various innovations, has been called a "literature of ideas." "Science fiction" is difficult to define as it includes a wide range of concepts and themes. James Blish wrote: "Wells used the term to cover what we would today call'hard' science fiction, in which a conscientious attempt to be faithful to known facts was the substrate on which the story was to be built, if the story was to contain a miracle, it ought at least not to contain a whole arsenal of them."Isaac Asimov said: "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology." According to Robert A. Heinlein, "A handy short definition of all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world and present, on a thorough understanding of the nature and significance of the scientific method."Lester del Rey wrote, "Even the devoted aficionado or fan—has a hard time trying to explain what science fiction is," and that the reason for there not being a "full satisfactory definition" is that "there are no delineated limits to science fiction."
Author and editor Damon Knight summed up the difficulty, saying "science fiction is what we point to when we say it." Mark C. Glassy described the definition of science fiction as U. S. Supreme Court Justice Potter Stewart did with the definition of pornography: "I know it when I see it." Science fiction had its beginnings in a time when the line between myth and fact was arguably more blurred than the present day. Written in the 2nd century CE by the satirist Lucian, A True Story contains many themes and tropes that are characteristic of contemporary science fiction, including travel to other worlds, extraterrestrial lifeforms, interplanetary warfare, artificial life; some consider it the first science-fiction novel. Some of the stories from The Arabian Nights, along with the 10th-century The Tale of the Bamboo Cutter and Ibn al-Nafis's 13th-century Theologus Autodidactus contain elements of science fiction. Products of the Age of Reason and the development of modern science itself, Johannes Kepler's Somnium, Francis Bacon's New Atlantis, Cyrano de Bergerac's Comical History of the States and Empires of the Moon and The States and Empires of the Sun, Margaret Cavendish's "The Blazing World", Jonathan Swift's Gulliver's Travels, Ludvig Holberg's Nicolai Klimii Iter Subterraneum and Voltaire's Micromégas are regarded as some of the first true science-fantasy works.
Indeed, Isaac Asimov and Carl Sagan considered Somnium the first science-fiction story. Following the 18th-century development of the novel as a literary form, Mary Shelley's books Frankenstein and The Last Man helped define the form of the science-fiction novel. Brian Aldiss has argued. Edgar Allan Poe wrote several stories considered science fiction, including "The Unparalleled Adventure of One Hans Pfaall" which featured a trip to the Moon. Jules Verne was noted for his attention to detail and scientific accuracy Twenty Thousand Leagues Under the Sea which predicted the contemporary nuclear submarine. In 1887, the novel El anacronópete by Spanish author Enrique Gaspar y Rimbau introduced the first time machine. Many critics consider H. G. Wells one of science fiction's most important authors, or "the Shakespeare of science fiction." His notable science-fiction works include The Time Machine, The Island of Doctor Moreau, The Invisible Man, The War of the Worlds. His science fiction imagined alien invasion, biological engineering and time travel.
In his non-fiction futurologist works he predicted the advent of airplanes, military tanks, nuclear weapons, satellite television, space travel, something resembling the World Wide Web. In 1912, Edgar Rice Burroughs published A Princess of Mars, the first of his three-decade-long planetary romance series of Barsoom novels, set on Mars and featuring John Carter as the hero. In 1926, Hugo Gernsback published the first American science-fiction magazine, Amazing Stories, in which he wrote: By'scientifiction' I mean the Jules Verne, H. G. Wells and Edgar Allan Poe type of story—a charming romance intermingled with scientific fact and prophetic vision... Not only do these amazing tales make tremendously interesting reading—they are always instructive, they supply knowledge... in a palatable form... New adventures pictured for us in the scientifiction of today are not at all impossible of realization tomorrow... Many great science stories destined to be of historical interest are still to be written...
Posterity will point to them as having blazed a new trail, not only in literature and fiction, but progress as well. In 1928, E. E. "Doc" Smith's first published work, The Skylark of Space, written in collaboration with Lee Hawkins Garby, appeared in Amazing Stories. It is called the first great space opera; the same year, Philip Francis Nowlan's original Buck Rogers story, Armageddon 2419 appeared in Amazing Stories. This was followed by the first serious science-fiction comic. In 1937, John W. Campbell became editor of Astounding Science Fiction, an event, sometimes conside
The Magellanic Clouds are two irregular dwarf galaxies visible in the Southern Celestial Hemisphere. Because both show signs of a bar structure, they are reclassified as Magellanic spiral galaxies; the two galaxies are: Large Magellanic Cloud 160,000 light-years away Small Magellanic Cloud 200,000 light years away The Magellanic Clouds have been known since the first millennium in Western Asia. The first preserved mention of the Large Magellanic Cloud is by the polymath Ibn Qutaybah, in his book on Al-Anwaa: "وأسفل من سهيل قدما سهيل. وفى مجرى قدمى سهيل، من خلفهما كواكب زهر كبار، لا ترى بالعراق، يسميها أهل تهامة الأعبار And below Canopus, there are the feet of Canopus, on their extension, behind them bright big stars, not seen in Iraq, the people of Tihama call them al-a`baar." Al Sufi, a professional astronomer, in 964 CE, in his Book of Fixed Stars, mentioned the same quote, but with a different spelling. Under Argo Navis, he quoted that "unnamed others have claimed that beneath Canopus there are two stars known as the'feet of Canopus', beneath those there are bright white stars that are unseen in Iraq nor Najd, that the inhabitants of Tihama call them al-Baqar, Ptolemy did not mention any of this so we do not know if this is true or false.".
Both Ibn Qutaybah and Al-Sufi were quoting from the former's contemporary and famed scientist Abu Hanifa Dinawari's lost work on Anwaa. Abu Hanifa was quoting earlier sources, which may be just travelers stories, hence Al-Sufi's comments about their veracity. In Sri Lanka, from ancient times, these clouds have been referred to as the Maha Mera Paruwathaya meaning "the great mountain", as they look like the peaks of a distant mountain range. In Europe, the Clouds were first reported by 16th century Italian authors Peter Martyr d'Anghiera and Andrea Corsali, both based on Portuguese voyages. Subsequently, they were reported by Antonio Pigafetta, who accompanied the expedition of Ferdinand Magellan on its circumnavigation of the world in 1519–1522. However, naming the clouds after Magellan did not become widespread until much later. In Bayer's Uranometria they are designated as nubecula major and nubecula minor. In the 1756 star map of the French astronomer Lacaille, they are designated as le Grand Nuage and le Petit Nuage.
Herschel in 1847 from Cape Observatory South Africa spent 4 years writing a 400-page report detailing over a thousand of the many stars and clusters which constitute the cloud which appeared to be a separate more distant group to the usual stars in the Milky Way, an early indication of separate galaxy. The Large Magellanic Cloud and its neighbour and relative, the Small Magellanic Cloud, are conspicuous objects in the southern hemisphere, looking like separated pieces of the Milky Way to the naked eye. 21° apart in the night sky, the true distance between them is 75,000 light-years. Until the discovery of the Sagittarius Dwarf Elliptical Galaxy in 1994, they were the closest known galaxies to our own; the LMC lies about 160,000 light years away, while the SMC is around 200,000. The LMC is about twice the diameter of the SMC. For comparison, the Milky Way is about 100,000 ly across; the total mass of these two galaxies is uncertain. Only a fraction of their gas seems to have coalesced into stars and they both have large dark matter halos.
One recent estimate of the total mass of the LMC is about 1/10 that of the Milky Way. That would make the LMC rather a large galaxy in the current observable universe. Since the size of nearby galaxies are skewed, the average mass can be a misleading statistic. In terms of rank, the LMC appears to be the fourth most massive member of over 50 galaxies in the local group. Suggesting that the Magellanic cloud system is not a part of the Milky Way is evidence that the SMC has been in orbit about the LMC for a long time; the Magellanic system seems most similar to the distinct NGC 3109 system, on the edge of the Local Group. Astronomers have long assumed that the Magellanic Clouds have orbited the Milky Way at their current distances, but evidence suggests that it is rare for them to come as close to the Milky Way as they are now. Observation and theoretical evidence suggest that the Magellanic Clouds have both been distorted by tidal interaction with the Milky Way as they travel close to it; the LMC maintains a clear spiral structure in radio-telescope images of neutral hydrogen.
Streams of neutral hydrogen connect them to the Milky Way and to each other, both resemble disrupted barred spiral galaxies. Their gravity has affected the Milky Way as well. Aside from their different structure and lower mass, they differ from our galaxy in two major ways. First, they are gas-rich, they are more metal-poor than the Milky Way. Both are noted for their nebulae and young stellar populations, but as in our own galaxy their stars range from the young to the old, indicating a long stellar formation history; the Large Magellanic Cloud was host galaxy to a supernova, the brightest observed in over four centuries. Measurements with the Hubble Space Telescope
Foundation and Earth
Foundation and Earth is a science fiction novel by American writer Isaac Asimov, the fifth novel of the Foundation series and chronologically the last in the series. It was published in 1986, four years after the first sequel to the Foundation trilogy, titled Foundation's Edge. Several centuries after the events of Second Foundation, two citizens of the Foundation seek to find Earth, the legendary planet where humans are said to have originated. Less is known about Earth than was the case in Foundation, when scholars still seem to know the location of'Sol'; the story can be read as a complete work in itself. Councilman Golan Trevize, historian Janov Pelorat, Blissenobiarella of the planet Gaia set out on a journey to find humanity's ancestral planet—Earth; the purpose of the journey is to settle Trevize's doubt of his decision, at the end of Foundation's Edge, to embrace the all-encompassing noosphere of Galaxia. First, they visit Comporellon, which claims to be the oldest inhabited planet in the galaxy.
Upon arrival, they negotiate their way out. While there, a historian gives them the coordinates of three Spacer planets, surmised to be close to Earth; the first Spacer planet they visit is Aurora, where Trevize is nearly killed by a pack of wild dogs, presumed to be the descendants of household pets reverted to wolf-like savagery. They escape when Bliss manipulates the dogs' emotions to psychologically compel a retreat, amplifying the fear induced by cries from one of the dogs that Trevize used his neuronic whip on. Next, they visit Solaria, where they find that the Solarians, who have survived the Spacer-Settler conflicts by clever retreat detailed in Asimov's novel Robots and Empire, have engineered themselves into self-reproducing hermaphrodites intolerant of human physical presence or contact, they have given themselves a natural ability to mentally channel great amounts of energy, use this as their sole source of power. The Solarians intentionally avoid having to interact with each other, except by holographic apparatus, reproduce only when necessary to replace the dead.
Bliss and Trevize are nearly killed by the Solarian Sarton Bander. While escaping, they acquire Bander's immature child, Fallom, in a state of panic because its robotic nursemaid, like all other robots on the estate, has lost power and stopped functioning due to the death of its master, carry her aboard their ship to prevent her execution by the Solarians as she would be surplus to their population requirements - a more mature child from another state would be chosen to take over Bander's estate; the crew now visit Melpomenia, the third and final Spacer coordinate they have, where the atmosphere has become reduced to a few thousandths of normal atmospheric pressure. Wearing space suits, they enter a library, find a plaque listing the names and coordinates of all fifty Spacer worlds. On the way back to the ship, they notice a moss has begun to grow around the seals of their space suits, just in time, surmise that the moss is feeding on minuscule leakages of carbon dioxide. Thus, they are able to eradicate the moss with a blaster and heavy UV-illumination so that no spores are unintentionally carried off the planet.
They plot the Spacer worlds on the ship's map, which form a rough sphere and conclude that the location of Earth must be near to the center of the sphere. This area turns out to have a binary star system, they arrive at the planet Alpha, which orbits Alpha Centauri and is all ocean except for an island 250 km long and 65 km wide on which live a small group of humans. In a reference to the radioactive Earth of Asimov's novel Pebble in the Sky, the restoration of Earth's soil was abandoned in favour of resettling the population to "New Earth", which the First Galactic Empire had been terraforming; the natives appear friendly, but secretly intend to kill the visitors with a microbiological agent, to prevent them from informing the rest of the galaxy of their existence. They are warned to escape before the agent can be activated, by a native woman who has formed an attraction to Trevize and was impressed by Fallom's ability to play a flute with just her mind. Now certain that Alpha Centauri is not Earth but near it, they approach a system close by, are puzzled by the strong similarities between this star and the larger sun of the Alpha Centauri system.
Asimov here is drawing attention to an astronomical curiosity: the nearest star system to Sol contains a star that has the same spectral type, G2 V, though Alpha Centauri A is a little larger and brighter. On the approach to Earth, they detect it to be radioactive and not capable of supporting life but, while trying to use the ship's computer to locate Solaria, Fallom calls Trevize's attention upon the moon, large enough to serve as a hideout for the forces that lived on Earth. There, they find R. Daneel Olivaw, who explains he has been paternalistically manipulating humanity since Elijah Baley's time, long before the Galactic Empire or Foundation, he thus caused the settlement of Alpha Centauri, the creation of Gaia and the creation of psychohistory, manipulated Trevize into making his decision at the end of Foundation's Edge. It is revealed that Daneel's positronic brain is deteriorating, he is unable to design a new brain as he
Isaac Asimov was an American writer and professor of biochemistry at Boston University. He was known for his works of popular science. Asimov was a prolific writer who wrote or edited more than 500 books and an estimated 90,000 letters and postcards, his books have been published in 9 of the 10 major categories of the Dewey Decimal Classification. Asimov wrote hard science fiction. Along with Robert A. Heinlein and Arthur C. Clarke, Asimov was considered one of the "Big Three" science fiction writers during his lifetime. Asimov's most famous work is the "Foundation" series; the Galactic Empire novels are set in earlier history of the same fictional universe as the Foundation series. With Foundation and Earth, he linked this distant future to the Robot stories, creating a unified "future history" for his stories much like those pioneered by Robert A. Heinlein and produced by Cordwainer Smith and Poul Anderson, he wrote hundreds of short stories, including the social science fiction novelette "Nightfall", which in 1964 was voted the best short science fiction story of all time by the Science Fiction Writers of America.
Asimov wrote the Lucky Starr series of juvenile science-fiction novels using the pen name Paul French. Asimov wrote mysteries and fantasy, as well as much nonfiction. Most of his popular science books explain concepts in a historical way, going as far back as possible to a time when the science in question was at its simplest stage. Examples include Guide to Science, the three-volume set Understanding Physics, Asimov's Chronology of Science and Discovery, he wrote on numerous other scientific and non-scientific topics, such as chemistry, mathematics, biblical exegesis, literary criticism. He was president of the American Humanist Association; the asteroid 5020 Asimov, a crater on the planet Mars, a Brooklyn elementary school, a literary award are named in his honor. Asimov's family name derives from the first part of azimy khleb, meaning the winter grain in which his great-great-great-grandfather dealt, with the Russian patronymic ending -ov added. Azimov is spelled Азимов in the Cyrillic alphabet.
When the family arrived in the United States in 1923 and their name had to be spelled in the Latin alphabet, Asimov's father spelled it with an S, believing this letter to be pronounced like Z, so it became Asimov. This inspired one of Asimov's short stories, "Spell My Name with an S."Asimov refused early suggestions of using a more common name as a pseudonym, believed that its recognizability helped his career. After becoming famous, he met readers who believed that "Isaac Asimov" was a distinctive pseudonym created by an author with a common name. Asimov was born in Petrovichi, Smolensk Oblast, Russian SFSR on an unknown date between October 4, 1919 and January 2, 1920, inclusive. Asimov celebrated his birthday on January 2. Asimov's parents were a family of Jewish millers, he was named Isaac after Isaac Berman. When he was born, his family lived in Petrovichi near Klimovichi, Gomel Governorate in the Russian Soviet Federative Socialist Republic. Asimov wrote of his father, "My father, for all his education as an Orthodox Jew, was not Orthodox in his heart", noting that "he didn't recite the myriad prayers prescribed for every action, he never made any attempt to teach them to me".
In 1921, Asimov and 16 other children in Petrovichi developed double pneumonia. Only Asimov survived, he had two younger siblings: a sister, a brother, vice-president of the Long Island Newsday. Asimov's family travelled to the United States via Liverpool on the SS Baltic, arriving on February 3, 1923 when he was three years old. Since his parents always spoke Yiddish and English with him, he never learned Russian, but he remained fluent in Yiddish as well as English. Growing up in Brooklyn, New York, Asimov taught himself to read at the age of five, his mother got him into first grade a year early by claiming he was born on September 7, 1919. In third grade he learned about the "error" and insisted on an official correction of the date to January 2. After becoming established in the U. S. his parents owned a succession of candy stores in which everyone in the family was expected to work. The candy stores sold newspapers and magazines, a fact that Asimov credited as a major influence in his lifelong love of the written word, as it presented him with an unending supply of new reading material as a child that he could not have otherwise afforded.
He became a naturalized U. S. citizen in 1928 at the age of eight. Asimov attended New York City public schools including Boys High School in Brooklyn. Graduating at 15, he attended the City College of New York for several days before accepting a scholarship at Seth Low Junior College, a branch of Columbia University in Downtown Brooklyn designed to absorb some of the Jewish and Italian-American students who applied to Columbia College the institution's primary undergraduate school for men with quotas on the number of admissions from those ethnic groups. A zoology major, Asimov switched to chemistry after his first semester as he disapproved of "dissecting an alley cat". After Seth Low Junior College closed in 1938, Asimov finished his Bachelor of Science degree at University Extension in 1939. After two rounds
The Andromeda Galaxy known as Messier 31, M31, or NGC 224, is a spiral galaxy 780 kiloparsecs from Earth, the nearest major galaxy to the Milky Way. Its name stems from the area of the Earth's sky; the virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at a trillion solar masses. The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%; this has been called into question by a 2018 study which cited a lower estimate on the mass of the Andromeda Galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass; the number of stars contained in the Andromeda Galaxy is estimated at one trillion, or twice the number estimated for the Milky Way.
The Milky Way and Andromeda galaxies are expected to collide in ~4.5 billion years, merging to form a giant elliptical galaxy or a large disc galaxy. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights when viewed from areas with moderate light pollution. Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy, in his Book of Fixed Stars as a "nebulous smear". Star charts of that period labeled it as the Little Cloud. In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations; the German philosopher Immanuel Kant in 1755 in his work Universal Natural History and Theory of the Heavens conjectured that the blurry spot was an island universe. In 1764, Charles Messier cataloged Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye.
In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. He believed Andromeda to be the nearest of all the "great nebulae", based on the color and magnitude of the nebula, he incorrectly guessed that it is no more than 2,000 times the distance of Sirius. In 1850, William Parsons, 3rd Earl of Rosse and made the first drawing of Andromeda's spiral structure. In 1864, William Huggins noted; the spectra of Andromeda displays a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. Andromeda's spectrum is similar to the spectra of individual stars, from this, it was deduced that Andromeda has a stellar nature. In 1885, a supernova was seen in the first and so far only one observed in that galaxy. At the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, was named accordingly. In 1887, Isaac Roberts took the first photographs of Andromeda, still thought to be a nebula within our galaxy.
Roberts mistook Andromeda and similar spiral nebulae as solar systems being formed. In 1912, Vesto Slipher used spectroscopy to measure the radial velocity of Andromeda with respect to our Solar System—the largest velocity yet measured, at 300 kilometres per second. In 1917, Heber Curtis observed a nova within Andromeda. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred elsewhere in the sky; as a result, he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the so-called "island universes" hypothesis, which held that spiral nebulae were independent galaxies. In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, the dimensions of the Universe. To support his claim of the Great Andromeda Nebula being, in fact, an external galaxy, Curtis noted the appearance of dark lanes within Andromeda which resembled the dust clouds in our own galaxy, as well as historical observations of Andromeda Galaxy's significant Doppler shift.
In 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside our galaxy at a distance of about 450,000 parsecs. Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of Andromeda; these were made using the 2.5-metre Hooker telescope, they enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our own galaxy, but an separate galaxy located a significant distance from the Milky Way. In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy. Baade identified two distinct populations of stars based on their metallicity, naming the young, high-velocity stars in the disk Type I and the older, red stars in the bulge Type II; this nomenclature was subsequently adopted for stars within the Milky Way, elsewhere.
Baade discovered that there were two types of Cepheid variables, which resulted in a doubling of the distance estimate to Andromeda, as well as the remainder o