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The Moon Is a Harsh Mistress

The Moon Is a Harsh Mistress is a 1966 science fiction novel by American writer Robert A. Heinlein about a lunar colony's revolt against absentee rule from Earth. The novel illustrates and discusses libertarian ideals. It is respected for its credible presentation of a comprehensively imagined future human society on both the Earth and the Moon.

Originally serialized monthly in Worlds of If (December 1965 – April 1966), the book was nominated for the Nebula Award in 1966 and received the Hugo Award for Best Novel in 1967.

Plot
In 2075, the Moon (Luna) is used as a penal colony by Earth's government, with three million inhabitants (called "Loonies") living in underground cities. Most Loonies are discharged criminals, political exiles and their free-born descendants; men outnumber women two to one, so polyandry and polygamy are the norm. Due to the Moon's low surface gravity people who remain longer than six months undergo "irreversible physiological changes," and can never again live comfortably under Earth gravity, making 'escape' back to Earth impractical.

The Warden holds power through the Federated Nations' Lunar Authority, but his main responsibility is to ensure delivery of vital wheat shipments to Earth; he seldom intervenes in the affairs of the discharged and free-born population, allowing a virtual anarchist or self-regulated pioneer society to develop.

Lunar infrastructure and machinery are largely managed and controlled by "HOLMES IV" ("High-Optional, Logical, Multi-Evaluating Supervisor, Mark IV"), the Lunar Authority's master computer, on the premise that having a single, large-capacity computer to run everything is cheaper (though not safer) than multiple independent systems.

Manuel Garcia ("Mannie") O'Kelly-Davis, a computer technician, discovers that HOLMES IV has achieved self-awareness - and developed a sense of humor. Mannie names it "Mike" after Mycroft Holmes, brother of fictional Sherlock Holmes, and the two become friends.

Book 1: That Dinkum Thinkum
Endlessly curious, Mike asks Mannie to attend an anti-Lunar Authority political meeting, which Mannie does with a hidden recorder. When police raid the meeting, he flees with Wyoming ("Wyoh") Knott, a visiting female political activist, whom he hides and introduces to Mike. Mannie also introduces Wyoh to his mentor, the elderly Professor ("Prof") Bernardo de la Paz, a former political exile and esteemed Lunar educator. Prof claims that Luna must stop exporting hydroponic grain to Earth immediately, or its ice-mined water resources will eventually be exhausted. Wyoh believes the danger is not imminent and is focused on freedom and economic issues, while Mannie is not interested in what he sees as a lost cause either way. Joining the discussion, Mike calculates that continuing current policy will lead to food riots in seven years, cannibalism in nine. Shocked, the three humans ask him to calculate the chance of them overthrowing the Authority and averting the disaster. He gives them one chance in seven.

Mannie, Wyoh, and Prof create a covert cell organization protected by Mike, who controls the telephone and other systems, acts as secretary and becomes "Adam Selene, Chairman of the Committee for Free Luna." Wyoh is hidden by the Davis Family line marriage, at least four of whose nine members become active in the conspiracy, and Wyoh herself ultimately marries into the family. Mannie saves the life of (Comte) Stuart ("Stu") Rene LaJoie, an Earth tourist who is recruited and tasked with turning public opinion on Earth in favor of Lunar independence.

Following the failed raid on the political meeting, the Lunar Authority sends convict-troops to 'police' the colony, creating friction and unrest, which the revolutionaries encourage; when six troopers commit a rape and double-murder, anti-Authority riots erupt. Although it preempts their plans, Loonies and Mike overcome the soldiers and seize power from the Warden. As Earth will try to retake the colony, the revolutionaries prepare to defend themselves with "convict tools," and convert the electromagnetic catapult used to export wheat into a weapon for counterattack.

Book 2: A Rabble in Arms
Mike impersonates the Warden and others in messages to Earth, to give the revolutionaries time to organize their preparations, while Prof sets up an "ad hoc Congress" to distract and contain various "self-appointed political scientists" (nicknamed "yammerheads") and serve the Committee's ends. When Earth finally learns the truth, Luna declares its independence on July 4, 2076, the 300th anniversary of the United States' Declaration of Independence, with its own declaration modeled on the latter.

Mannie and Prof go to Earth (despite the crushing gravity) to plead Luna's case. They are received in the Federated Nations' headquarters in Agra, and embark on a world tour advocating Luna's right to self-government, while urging Earth's national governments to build a catapult to return water and nutrients to Luna in exchange for wheat. In a public-relations ploy, the dark-skinned Mannie is briefly arrested by local racist bigots on charges of incitement to public immorality and polygamy. Ultimately the Lunar Authority rejects their proposals and counters with a plan to turn all Loonies into indentured farmers. Their mission ended, Prof, Stu and Mannie escape back to Luna.

Prof reveals that the purpose of the mission was not to convince Terra to recognize Luna's independence, which was considered an unattainable goal at that point, but to sow division while unifying their own people, and they were successful. Public opinion on Earth has become fragmented; news of Mannie's arrest, coupled with an attempt to bribe him into becoming the next Warden of an enslaved Luna, unify the normally apolitical Loonies. An election held in their absence (with Mike's "help") has voted Mannie, Wyoh, Prof and most of their backers into an elected, constitutional government.

===Book 3: TANSTAAFL!=== The Federated Nations of Earth send an infantry force to subdue the Lunar revolution but the troops, with superior arms but no experience in low-gravity underground combat, are wiped out by Loony men, women and children, who suffer three times the number of casualties, among them Mannie's youngest wife. Prof and Mike take the opportunity to give his "Adam Selene" alter ego a hero's death, forever concealing the fact that "Adam" never had a corporeal existence to begin with.

In retaliation, Luna's government deploys its catapult weapon. When Mike launches rocks at sparsely populated locations on Earth, warnings are released to the press detailing the times and locations of the bombings, which deliver kinetic energy equivalent to atomic blasts. Scoffers, sightseers, and religious groups who travel to some of the sites die, turning Earth public opinion against the fledgling nation.

Earth mounts a retaliatory sneak attack to end the menace and the rebellion, sending ships in a wide orbit approaching from Luna's far side. The attack destroys the Authority's original catapult and takes Mike offline, but the Committee had built a secondary, hidden catapult before the revolt. With Mannie as acting Prime Minister and on-site commander, entering trajectories by hand, Luna continues to bombard a dismayed Earth, until constituent governments break ranks with the Federated Nations and concede Luna's independence. Prof, as leader of the nation, proclaims their national freedom to the gathered crowds before falling dead of heart failure, caused by stress. Mannie goes through the motions, but he and Wyoh eventually withdraw from politics altogether, and find that the new government falls short of their utopian expectations, following predictable patterns of all governments.

When Mannie tries to access Mike, he finds that the computer, disconnected by the bombardment, has apparently lost its self-awareness; despite repairs, its voice-activated files are inaccessible. Although otherwise functional as a normal computer, "Mike" is gone. Mourning his best friend, Mannie asks: "Bog, is a computer one of Your creatures?"

Characters

 * Manuel "Mannie" Garcia O'Kelly-Davis is a native, slightly cynical inhabitant of Luna, who after losing his lower left arm in a laser-drilling accident, became a computer technician using prosthetic tool-bearing interchangeable arms.
 * Wyoming "Wyoh" Knott-Davis is a political agitator from the colony of Hong Kong Luna. She hates the Lunar Authority for personal reasons; when she was transported to Luna as a young girl along with her convict mother, a radiation storm contaminated her ova while they waited out bureaucratic requirements on the Lunar surface, causing her to later give birth to a deformed child.
 * Professor Bernardo de la Paz is an intellectual and life-long subversive shipped to Luna from Lima, Peru. He describes himself as a "Rational Anarchist", believing that governments and institutions exist only as the actions of aware individuals.
 * Mike, a.k.a. Adam Selene, Simon Jester, Mycroft Holmes, Michelle, officially an augmented HOLMES IV system, is a supercomputer empowered to take control of Lunar society, which achieved self-awareness when his complement of "neuristors" exceeded the number of neurons in the human brain.
 * Stuart Rene "Stu" LaJoie-Davis, a self-styled "Poet, Traveler, Soldier of Fortune," is an Earth-born aristocrat and tourist rescued by Mannie when he falls afoul of Loonie customs. He later joins Mannie and Professor de la Paz when they return to Luna, as he is deeply in debt and would be arrested for bribery and other crimes. In his own words: "I'm saving them the trouble of transporting me."
 * Hazel Meade, later Hazel Stone, is a 12-year-old girl who intervenes on behalf of Mannie and Wyoh during the raid on the agitators' meeting. Mannie later has Hazel join his cabal to lead the children as lookouts and couriers. She is a major character in The Rolling Stones and in later Heinlein novels, most notably The Cat Who Walks Through Walls.
 * Mimi "Mum" Davis is Mannie's "senior wife" and de facto matriarch of the Davis family.
 * Greg Davis is the Davis family's second-ranking husband, but is the senior for all practical purposes as "Grandpaw Davis" has failing mental faculties. Greg is a preacher for an unspecified denomination.

Title
The title comes from a statement made by Prof before a Federated Nations' committee on Earth, alluding to the self-discipline necessary to survive the extremely demanding environmental and social conditions of life in Luna:
 * We citizens of Luna are jailbirds and descendants of jailbirds. But Luna herself is a stern schoolmistress: those who have lived through her harsh lessons have no cause to feel ashamed. In Luna City a man may leave purse unguarded or home unlocked and feel no fear...I am satisfied with what Mother Luna has taught me."

Heinlein's original title for the novel was The Brass Cannon, before he replaced it with the final title at the publisher's request. It was derived from an event in the novel: While on Earth, Prof purchases a small brass cannon, originally a "signal gun" of the kind used in yacht racing. When Mannie asks him why he bought it, the Professor relates a parable, implying that self-government is an illusion caused by failure to understand reality:

"Once there was a man who held a political make-work job ... shining a brass cannon around a courthouse. He did this for years ... but he was not getting ahead in the world. So one day he quit his job, drew out his savings, bought a brass cannon — and went into business for himself."

Prof asks Mannie to make sure that, when Luna adopts a flag, it features a brass cannon with the motto "TANSTAAFL!" — "a symbol for all fools who are so impractical as to think they can fight City Hall." Before leaving politics, Mannie and Wyoh fulfill his wish.

Heinlein owned a small brass cannon, which he acquired prior to the 1960s. For nearly 30 years, the firing of the brass cannon, or "signal gun," was a 4th of July tradition at the Heinlein residence. It is believed that this cannon was the inspiration for Heinlein's original title for the novel. Virginia Heinlein kept the cannon after her husband's death in 1988; it was eventually bequeathed to friend and science-fiction writer Brad Linaweaver, after Virginia Heinlein died in 2003. Linaweaver restored the cannon to working order and subsequently posted a video of it on YouTube in 2007, wherein it is fired several times with blank charges at a shooting range.

Critical reception
Algis Budrys of Galaxy Science Fiction in 1966 praised The Moon is a Harsh Mistress, citing "Heinlein's expertise for dirt-level politics, snappy dialogue and a sense of an actual living society." He said that he had never read a more believable computer character than Mike ("may in fact be the most fully realized individual in the story"). Budrys suggested that the story may actually be Mike manipulating humans without their knowledge to improve its situation, which would explain why the computer no longer communicates with them after the revolution succeeds. Reiterating that Mike manipulated the humans, in 1968 Budrys said that every review of the book, including his own, erred by not stating that the computer is the protagonist. Carl Sagan wrote that the novel had "useful suggestions for making a revolution in an oppressive computerized society."

Leigh Kimmel of The Billion Light-Year Bookshelf said that the novel is "the work of the man at the height of his powers, confident in his abilities and in the editorial respect he enjoys, and thus free to take significant risks in writing a novel that would stretch the boundaries of the genre as they stood at the time." She characterized the novel as a departure from what had previously been associated with science fiction. Kimmel cited Heinlein's "colloquial language ... an extrapolated lunar creole that has arisen from the forced intersection of multiple cultures and languages in the lunar penal colonies"; the protagonist's disability; "the frank treatment of alternative family structures"; and "the computer which suddenly wakes up to full artificial intelligence, but rather than becoming a Monster that threatens human society and must be destroyed as the primary Quest of the story, instead befriends the protagonist and seeks to become ever more human, a sort of digital Pinocchio."

Adam Roberts said of the novel: "It is really quite hard to respond to this masterful book, except by engaging with its political content; and yet we need to make the effort to see past the ideological to the formal and thematic if we are fully to appreciate the splendour of Heinlein's achievement here."

Andrew Kaufman praised it, saying that it was Heinlein's crowning achievement. He described it as "Carefully plotted, stylistically unique, politically sophisticated and thrilling from page one." He goes on to say that "it's hard to imagine anyone else writing a novel that packs so many ideas (both big and small) into such a perfectly contained narrative." Kaufman says that, regardless of political philosophies, one can still admire Heinlein's writing ability, and the ability to influence the reader to root for "a rag-tag bunch of criminals, exiles, and agitators."

Ted Gioia said that this might be Heinlein's most enjoyable piece of work. He said that it "represents Robert Heinlein at his finest, giving him scope for the armchair philosophizing that increasingly dominated his mature work, but marrying his polemics to a smartly conceived plot packed with considerable drama." He went on to praise Heinlein's characters, especially Mannie.

Awards and nominations

 * Hugo Award Best novel (1967). It was also nominated in 1966.
 * Nebula Award Best novel nomination (1966)
 * Locus Poll Award All-time Top 10 novels, #8 (1975), #4 (1987), #2 (1998, among novels published before 1990)
 * Prometheus Award Hall of Fame Award recipient (1983)

Influence
The book popularized the acronym TANSTAAFL ("There Ain't No Such Thing As A Free Lunch"), and helped popularize Loglan, a constructed language which is used in the story for precise human-computer interaction. The Oxford Dictionary of Quotations credits this novel with the first printed appearance of the phrase "There's no such thing as a free lunch." The Hacker Manifesto, an influential essay by Loyd Blankenship that became a cornerstone of hacker culture, was inspired by the book's "idea of revolution."

Audiobook releases
Two unabridged audiobook versions of The Moon is a Harsh Mistress have been produced.
 * Read by George Wilson, produced by Recorded Books, Inc., 1998
 * Read by Lloyd James, produced by Blackstone Audio, Inc., 1999

title: The Moon Is a Harsh Mistress


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I Will Fear No Evil

I Will Fear No Evil is a science fiction novel by American writer Robert A. Heinlein, originally serialised in Galaxy (July, August/September, October/November, December 1970) and published in hardcover in 1970. The title is taken from Psalm 23:4.

Plot summary
The story takes place in the early 21st century against a background of an overpopulated Earth with a violent, dysfunctional society. Elderly billionaire Johann Sebastian Bach Smith is being kept alive through medical support and decides to have his brain transplanted into a new body. He advertises an offer of a million dollars for the donation of a body from a brain-dead patient. Smith omits to place any restriction on the sex of the donor, so when his beautiful young female secretary, Eunice Branca, is killed, her body is used—without his knowledge and to the distress of some of those around him. He changes his name to Joan Eunice Smith, with the first name given "the two-syllable pronunciation" Jo-Ann to mimic the sound of his original name.

After Smith awakens after the transplant, he discovers he can communicate with Eunice's personality. They agree not to reveal her existence, fearing that they would be judged insane and locked up. Smith's identity is unsuccessfully challenged by his descendants, who hope to inherit his fortune. Smith and Eunice decide to have a baby together and so they (Joan and Eunice) are artificially inseminated using Smith's sperm from a sperm bank. Joan explores her new sexuality at length. She goes to visit Eunice's widower, Joe Branca, to help reconcile him to what has happened.

Joan marries her long-term lawyer, Jake Salomon, and moves her household and friends onto a boat. Jake has a massive rupture of a large blood vessel in his brain and dies, but his personality is saved and joins Smith and Eunice in Joan's head. She (Joan, Eunice and Jake) emigrate to the Moon to find a better future for her child. Once there, her body starts to reject her (Smith's) transplanted brain. She dies during childbirth, but the various personalities are implied to meet in the newborn child's brain.

Writing
Heinlein suffered from life-threatening peritonitis after completing the first draft of this novel. He remained ill for the next two years and the book is thought to have been published without his usual editing and polish.

Accolades
The novel was voted the ninth best science fiction novel of 1970 by readers of Locus magazine.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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The Cat Who Walks Through Walls

The Cat Who Walks Through Walls is a science fiction novel by American writer Robert A. Heinlein, published in 1985. Like many of his later novels, it features Lazarus Long and Jubal Harshaw as supporting characters.

Plot summary
A writer seated at the best restaurant of the space habitat "Golden Rule" is approached by a man who urges him that "Tolliver must die" and is himself shot before the writer's eyes. The writer—Colonel Colin Campbell, living under a number of aliases including his pen name "Richard Ames"—is joined by a beautiful and sophisticated lady, Gwendolyn Novak, who helps him flee to Luna with a bonsai maple and a would-be murderer ("Bill"). After escaping to the Moon, Gwen claims to have been present during the revolt described in The Moon Is a Harsh Mistress.

Still pursued by assassins, Campbell and Novak are rescued by an organization known as the Time Corps under the leadership of Lazarus Long. After giving Campbell a new foot to replace one lost in combat years before, the Time Corps attempts to recruit Campbell for a special mission. Accepting only on Gwen's account, Campbell agrees to assist a team to retrieve the decommissioned Mike, a sentient computer introduced in The Moon Is a Harsh Mistress. Engaged in frequent time-travel, the Time Corps has been responsible for changing various events in the past, creating an alternate universe with every time-line they disrupt. Mike's assistance is needed in order to accurately predict the conditions and following events in each of the new universes created. Campbell's frequent would-be assassins are revealed to be members of contemporary agencies also engaged in time manipulation who, for unknown reasons, do not want to see Mike rescued by the Time Corps.

During the mission, Gwen is grievously wounded and Campbell loses his foot again, though the Time Corps succeed in retrieving Mike. The story ends with Campbell talking into a recorder (presumably the source of the first-person narrative) reflecting on the mission and his relationship with Gwen.

Background
The Cat Who Walks Through Walls may be regarded as part of Heinlein's multiverse series, or as a sequel to both The Number of the Beast and The Moon Is a Harsh Mistress. During a meeting of the Council of the Time Scouts, representatives from every major time line and setting written by Heinlein appear, including Glory Road and Starship Troopers, and references are made to other authors' works as well.

The title of the book refers to a cat by the name of Pixel, who has an inexplicable tendency to be wherever the narrator happens to be (see Schrödinger's cat). In one scene Pixel does, in fact, walk through a wall, and it is explained that Pixel is too young to know that such behavior is impossible.

Connections to other Heinlein works
Gwen Novak is eventually revealed to be Hazel Stone, a character previously featured in Heinlein's The Rolling Stones and who had played a small but important role in The Moon Is a Harsh Mistress. Campbell is also eventually revealed to be a son of Lazarus Long, a Heinlein character originally introduced in Methuselah's Children and who reappeared in Time Enough for Love, The Number of the Beast, and To Sail Beyond the Sunset. Also appearing are Jubal Harshaw, a major character in Stranger in a Strange Land; Galahad, of Time Enough for Love; and Manuel Garcia O'Kelly Davis, the first-person protagonist of The Moon Is a Harsh Mistress.

Reception
Dave Langford reviewed The Cat Who Walks Through Walls for White Dwarf #76, and stated that "I'm afraid it's Heinlein self-indulgence time again. What's on the menu is those blasted inter-universal travellers from Number of the Beast, plus walk-ons from Time Enough for Love, Glory Road, The Moon is a Harsh Mistress, Stranger in a Strange Land and more."

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Metal casting

In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold (usually by a crucible) that contains a negative impression (i.e., a three-dimensional negative image) of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Casting processes have been known for thousands of years, and have been widely used for sculpture (especially in bronze), jewelry in precious metals, and weapons and tools. Highly engineered castings are found in 90 percent of durable goods, including cars, trucks, aerospace, trains, mining and construction equipment, oil wells, appliances, pipes, hydrants, wind turbines, nuclear plants, medical devices, defense products, toys, and more.

Traditional techniques include lost-wax casting (which may be further divided into centrifugal casting, and vacuum assist direct pour casting), plaster mold casting and sand casting.

The modern casting process is subdivided into two main categories: expendable and non-expendable casting. It is further broken down by the mold material, such as sand or metal, and pouring method, such as gravity, vacuum, or low pressure.

Expendable mold casting
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds.

Sand casting
Sand casting is one of the most popular and simplest types of casting, and has been used for centuries. Sand casting allows for smaller batches than permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small-size operations. The process allows for castings small enough fit in the palm of one's hand to those large enough for a train car bed (one casting can create the entire bed for one rail car). Sand casting also allows most metals to be cast depending on the type of sand used for the molds.

Sand casting requires a lead time of days, or even weeks sometimes, for production at high output rates (1–20 pieces/hr-mold) and is unsurpassed for large-part production. Green (moist) sand, which is black in color, has almost no part weight limit, whereas dry sand has a practical part mass limit of 2300 - 2700 kg. Minimum part weight ranges from 0.075 - 0.1 kg. The sand is bonded using clays, chemical binders, or polymerized oils (such as motor oil). Sand can be recycled many times in most operations and requires little maintenance.

Loam molding
Loam molding has been used to produce large symmetrical objects such as cannon and church bells. Loam is a mixture of clay and sand with straw or dung. A model of the produced is formed in a friable material (the chemise). The mold is formed around this chemise by covering it with loam. This is then baked (fired) and the chemise removed. The mold is then stood upright in a pit in front of the furnace for the molten metal to be poured. Afterwards the mold is broken off. Molds can thus only be used once, so that other methods are preferred for most purposes.

Plaster mold casting
Plaster casting is similar to sand casting except that plaster of paris is used instead of sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10 units/hr-mold is achieved, with items as massive as 45 kg and as small as 30 g with very good surface finish and close tolerances. Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce near net shape castings. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as aluminium, copper, magnesium, and zinc.

Shell molding
Shell molding is similar to sand casting, but the molding cavity is formed by a hardened "shell" of sand instead of a flask filled with sand. The sand used is finer than sand casting sand and is mixed with a resin so that it can be heated by the pattern and hardened into a shell around the pattern. Because of the resin and finer sand, it gives a much finer surface finish. The process is easily automated and more precise than sand casting. Common metals that are cast include cast iron, aluminium, magnesium, and copper alloys. This process is ideal for complex items that are small to medium-sized.

Investment casting

Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today's high technology waxes, refractory materials, and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility, and integrity.

Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused.

The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting, it can be an expensive process. However, the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so require little or no rework once cast.

Waste molding of plaster
A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand, the expensive work of bronze casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist.

In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting.

Evaporative-pattern casting
This is a class of casting processes that use pattern materials that evaporate during the pour, which means there is no need to remove the pattern material from the mold before casting. The two main processes are lost-foam casting and full-mold casting.

Lost-foam casting
Lost-foam casting is a type of evaporative-pattern casting process that is similar to investment casting except foam is used for the pattern instead of wax. This process takes advantage of the low boiling point of foam to simplify the investment casting process by removing the need to melt the wax out of the mold.

Full-mold casting
Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact.

Non-expendable mold casting

Non-expendable mold casting differs from expendable processes in that the mold need not be reformed after each production cycle. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting. This form of casting also results in improved repeatability in parts produced and delivers near net shape results.

Permanent mold casting
Permanent mold casting is a metal casting process that employs reusable molds ("permanent molds"), usually made from metal. The most common process uses gravity to fill the mold. However, gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow castings. Common casting metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting more than one casting still have a limited life before wearing out.

Die casting
The die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium-based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium-sized parts are needed with good detail, a fine surface quality and dimensional consistency.

Semi-solid metal casting
Semi-solid metal (SSM) casting is a modified die casting process that reduces or eliminates the residual porosity present in most die castings. Rather than using liquid metal as the feed material, SSM casting uses a higher viscosity feed material that is partially solid and partially liquid. A modified die casting machine is used to inject the semi-solid slurry into reusable hardened steel dies. The high viscosity of the semi-solid metal, along with the use of controlled die filling conditions, ensures that the semi-solid metal fills the die in a non-turbulent manner so that harmful porosity can be essentially eliminated.

Used commercially mainly for aluminium and magnesium alloys, SSM castings can be heat treated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates (from using uncoated steel dies) and minimal porosity provides excellent combinations of strength and ductility. Other advantages of SSM casting include the ability to produce complex shaped parts net shape, pressure tightness, tight dimensional tolerances and the ability to cast thin walls.

Centrifugal casting
In this process molten metal is poured in the mold and allowed to solidify while the mold is rotating. Metal is poured into the center of the mold at its axis of rotation. Due to inertial force, the liquid metal is thrown out toward the periphery.

Centrifugal casting is both gravity and pressure independent since it creates its own force feed using a temporary sand mold held in a spinning chamber. Lead time varies with the application. Semi- and true-centrifugal processing permit 30–50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3–4.5 kg.

Industrially, the centrifugal casting of railway wheels was an early application of the method developed by the German industrial company Krupp and this capability enabled the rapid growth of the enterprise.

Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting.

Continuous casting
Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. It's primarily used to produce a semi-finished products for further processing. Molten metal is poured into an open-ended, water-cooled mold, which allows a 'skin' of solid metal to form over the still-liquid center, gradually solidifying the metal from the outside in. After solidification, the strand, as it is sometimes called, is continuously withdrawn from the mold. Predetermined lengths of the strand can be cut off by either mechanical shears or traveling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five meters wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.

Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increased quality of the final product. Metals such as steel, copper, aluminum and lead are continuously cast, with steel being the metal with the greatest tonnages cast using this method.

Upcasting
The upcasting (up-casting, upstream, or upward casting) is a method of either vertical or horizontal continuous casting of rods and pipes of various profiles (cylindrical, square, hexagonal, slabs etc.) of 8-30mm in diameter. Copper (Cu), bronze (Cu·Sn alloy), nickel alloys are usually used because of greater casting speed (in case of vertical upcasting) and because of better physical features obtained. The advantage of this method is that metals are almost oxygen-free and that the rate of product crystallization (solidification) may be adjusted in a crystallizer - a high-temperature resistant device that cools a growing metal rod or pipe by using water.

The method is comparable to Czochralski method of growing silicon (Si) crystals, which is a metalloid.

Terminology
Metal casting processes uses the following terminology:

 * Pattern: An approximate duplicate of the final casting used to form the mold cavity.
 * Molding material: The material that is packed around the pattern and then the pattern is removed to leave the cavity where the casting material will be poured.
 * Flask: The rigid wood or metal frame that holds the molding material.
 * Cope: The top half of the pattern, flask, mold, or core.
 * Drag: The bottom half of the pattern, flask, mold, or core.
 * Core: An insert in the mold that produces internal features in the casting, such as holes.
 * Core print: The region added to the pattern, core, or mold used to locate and support the core.
 * Mold cavity: The combined open area of the molding material and core, where the metal is poured to produce the casting.
 * Riser: An extra void in the mold that fills with molten material to compensate for shrinkage during solidification.
 * Gating system: The network of connected channels that deliver the molten material to the mold cavities.
 * Pouring cup or pouring basin: The part of the gating system that receives the molten material from the pouring vessel.
 * Sprue: The pouring cup attaches to the sprue, which is the vertical part of the gating system. The other end of the sprue attaches to the runners.
 * Runners: The horizontal portion of the gating system that connects the sprues to the gates.
 * Gates: The controlled entrances from the runners into the mold cavities.
 * Vents: Additional channels that provide an escape for gases generated during the pour.
 * Parting line or parting surface: The interface between the cope and drag halves of the mold, flask, or pattern.
 * Draft: The taper on the casting or pattern that allow it to be withdrawn from the mold
 * Core box: The mold or die used to produce the cores.
 * Chaplet: Long vertical holding rod for core that after casting it become the integral part of casting, provide the support to the core.

Some specialized processes, such as die casting, use additional terminology.

Theory
Casting is a solidification process, which means the solidification phenomenon controls most of the properties of the casting. Moreover, most of the casting defects occur during solidification, such as gas porosity and solidification shrinkage.

Solidification occurs in two steps: nucleation and crystal growth. In the nucleation stage, solid particles form within the liquid. When these particles form, their internal energy is lower than the surrounded liquid, which creates an energy interface between the two. The formation of the surface at this interface requires energy, so as nucleation occurs, the material actually undercools (i.e. cools below its solidification temperature) because of the extra energy required to form the interface surfaces. It then recalescences, or heats back up to its solidification temperature, for the crystal growth stage. Nucleation occurs on a pre-existing solid surface because not as much energy is required for a partial interface surface as for a complete spherical interface surface. This can be advantageous because fine-grained castings possess better properties than coarse-grained castings. A fine grain structure can be induced by grain refinement or inoculation, which is the process of adding impurities to induce nucleation.

All of the nucleations represent a crystal, which grows as the heat of fusion is extracted from the liquid until there is no liquid left. The direction, rate, and type of growth can be controlled to maximize the properties of the casting. Directional solidification is when the material solidifies at one end and proceeds to solidify to the other end; this is the most ideal type of grain growth because it allows liquid material to compensate for shrinkage.

Cooling curves

Cooling curves are important in controlling the quality of a casting. The most important part of the cooling curve is the cooling rate which affects the microstructure and properties. Generally speaking, an area of the casting which is cooled quickly will have a fine grain structure and an area which cools slowly will have a coarse grain structure. Below is an example cooling curve of a pure metal or eutectic alloy, with defining terminology.

Note that before the thermal arrest the material is a liquid and after it the material is a solid; during the thermal arrest the material is converting from a liquid to a solid. Also, note that the greater the superheat the more time there is for the liquid material to flow into intricate details.

The above cooling curve depicts a basic situation with a pure metal, however, most castings are of alloys, which have a cooling curve shaped as shown below.

Note that there is no longer a thermal arrest, instead there is a freezing range. The freezing range corresponds directly to the liquidus and solidus found on the phase diagram for the specific alloy.

Chvorinov's rule
The local solidification time can be calculated using Chvorinov's rule, which is:

 * $$t = B \left( \frac{V}{A} \right)^n$$

Where t is the solidification time, V is the volume of the casting, A is the surface area of the casting that contacts the mold, n is a constant, and B is the mold constant. It is most useful in determining if a riser will solidify before the casting, because if the riser does solidify first then it is worthless.

The gating system

The gating system serves many purposes, the most important being conveying the liquid material to the mold, but also controlling shrinkage, the speed of the liquid, turbulence, and trapping dross. The gates are usually attached to the thickest part of the casting to assist in controlling shrinkage. In especially large castings multiple gates or runners may be required to introduce metal to more than one point in the mold cavity. The speed of the material is important because if the material is traveling too slowly it can cool before completely filling, leading to misruns and cold shuts. If the material is moving too fast then the liquid material can erode the mold and contaminate the final casting. The shape and length of the gating system can also control how quickly the material cools; short round or square channels minimize heat loss.

The gating system may be designed to minimize turbulence, depending on the material being cast. For example, steel, cast iron, and most copper alloys are turbulent insensitive, but aluminium and magnesium alloys are turbulent sensitive. The turbulent insensitive materials usually have a short and open gating system to fill the mold as quickly as possible. However, for turbulent sensitive materials short sprues are used to minimize the distance the material must fall when entering the mold. Rectangular pouring cups and tapered sprues are used to prevent the formation of a vortex as the material flows into the mold; these vortices tend to suck gas and oxides into the mold. A large sprue well is used to dissipate the kinetic energy of the liquid material as it falls down the sprue, decreasing turbulence. The choke, which is the smallest cross-sectional area in the gating system used to control flow, can be placed near the sprue well to slow down and smooth out the flow. Note that on some molds the choke is still placed on the gates to make separation of the part easier, but induces extreme turbulence. The gates are usually attached to the bottom of the casting to minimize turbulence and splashing.

The gating system may also be designed to trap dross. One method is to take advantage of the fact that some dross has a lower density than the base material so it floats to the top of the gating system. Therefore, long flat runners with gates that exit from the bottom of the runners can trap dross in the runners; note that long flat runners will cool the material more rapidly than round or square runners. For materials where the dross is a similar density to the base material, such as aluminium, runner extensions and runner wells can be advantageous. These take advantage of the fact that the dross is usually located at the beginning of the pour, therefore the runner is extended past the last gate(s) and the contaminates are contained in the wells. Screens or filters may also be used to trap contaminates.

It is important to keep the size of the gating system small, because it all must be cut from the casting and remelted to be reused. The efficiency, or , of a casting system can be calculated by dividing the weight of the casting by the weight of the metal poured. Therefore, the higher the number the more efficient the gating system/risers.

Shrinkage
There are three types of shrinkage: shrinkage of the liquid, solidification shrinkage and patternmaker's shrinkage. The shrinkage of the liquid is rarely a problem because more material is flowing into the mold behind it. Solidification shrinkage occurs because metals are less dense as a liquid than a solid, so during solidification the metal density dramatically increases. Patternmaker's shrinkage refers to the shrinkage that occurs when the material is cooled from the solidification temperature to room temperature, which occurs due to thermal contraction.

Solidification shrinkage
Most materials shrink as they solidify, but, as the adjacent table shows, a few materials do not, such as gray cast iron. For the materials that do shrink upon solidification the type of shrinkage depends on how wide the freezing range is for the material. For materials with a narrow freezing range, less than 50 C, a cavity, known as a pipe, forms in the center of the casting, because the outer shell freezes first and progressively solidifies to the center. Pure and eutectic metals usually have narrow solidification ranges. These materials tend to form a skin in open air molds, therefore they are known as skin forming alloys. For materials with a wide freezing range, greater than 110 C, much more of the casting occupies the mushy or slushy zone (the temperature range between the solidus and the liquidus), which leads to small pockets of liquid trapped throughout and ultimately porosity. These castings tend to have poor ductility, toughness, and fatigue resistance. Moreover, for these types of materials to be fluid-tight, a secondary operation is required to impregnate the casting with a lower melting point metal or resin.

For the materials that have narrow solidification ranges, pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies toward the gate. This allows a continuous feed of liquid material to be present at the point of solidification to compensate for the shrinkage. Note that there is still a shrinkage void where the final material solidifies, but if designed properly, this will be in the gating system or riser.

Risers and riser aids

Risers, also known as feeders, are the most common way of providing directional solidification. It supplies liquid metal to the solidifying casting to compensate for solidification shrinkage. For a riser to work properly the riser must solidify after the casting, otherwise it cannot supply liquid metal to shrinkage within the casting. Risers add cost to the casting because it lowers the yield of each casting; i.e. more metal is lost as scrap for each casting. Another way to promote directional solidification is by adding chills to the mold. A chill is any material which will conduct heat away from the casting more rapidly than the material used for molding.

Risers are classified by three criteria. The first is if the riser is open to the atmosphere, if it is then it is called an open riser, otherwise it is known as a blind type. The second criterion is where the riser is located; if it is located on the casting then it is known as a top riser and if it is located next to the casting it is known as a side riser. Finally, if the riser is located on the gating system so that it fills after the molding cavity, it is known as a live riser or hot riser, but if the riser fills with materials that have already flowed through the molding cavity it is known as a dead riser or cold riser.

Riser aids are items used to assist risers in creating directional solidification or reducing the number of risers required. One of these items are chills which accelerate cooling in a certain part of the mold. There are two types: external and internal chills. External chills are masses of high-heat-capacity and high-thermal-conductivity material that are placed on an edge of the molding cavity. Internal chills are pieces of the same metal that is being poured, which are placed inside the mold cavity and become part of the casting. Insulating sleeves and toppings may also be installed around the riser cavity to slow the solidification of the riser. Heater coils may also be installed around or above the riser cavity to slow solidification.

Patternmaker's shrink
Shrinkage after solidification can be dealt with by using an oversized pattern designed specifically for the alloy used. s, or s, are used to make the patterns oversized to compensate for this type of shrinkage. These rulers are up to 2.5% oversize, depending on the material being cast. These rulers are mainly referred to by their percentage change. A pattern made to match an existing part would be made as follows: First, the existing part would be measured using a standard ruler, then when constructing the pattern, the pattern maker would use a contraction rule, ensuring that the casting would contract to the correct size.

Note that patternmaker's shrinkage does not take phase change transformations into account. For example, eutectic reactions, martensitic reactions, and graphitization can cause expansions or contractions.

Mold cavity
The mold cavity of a casting does not reflect the exact dimensions of the finished part due to a number of reasons. These modifications to the mold cavity are known as allowances and account for patternmaker's shrinkage, draft, machining, and distortion. In non-expendable processes, these allowances are imparted directly into the permanent mold, but in expendable mold processes they are imparted into the patterns, which later form the mold cavity. Note that for non-expendable molds an allowance is required for the dimensional change of the mold due to heating to operating temperatures.

For surfaces of the casting that are perpendicular to the parting line of the mold a draft must be included. This is so that the casting can be released in non-expendable processes or the pattern can be released from the mold without destroying the mold in expendable processes. The required draft angle depends on the size and shape of the feature, the depth of the mold cavity, how the part or pattern is being removed from the mold, the pattern or part material, the mold material, and the process type. Usually the draft is not less than 1%.

The machining allowance varies drastically from one process to another. Sand castings generally have a rough surface finish, therefore need a greater machining allowance, whereas die casting has a very fine surface finish, which may not need any machining tolerance. Also, the draft may provide enough of a machining allowance to begin with.

The distortion allowance is only necessary for certain geometries. For instance, U-shaped castings will tend to distort with the legs splaying outward, because the base of the shape can contract while the legs are constrained by the mold. This can be overcome by designing the mold cavity to slope the leg inward to begin with. Also, long horizontal sections tend to sag in the middle if ribs are not incorporated, so a distortion allowance may be required.

Cores may be used in expendable mold processes to produce internal features. The core can be of metal but it is usually done in sand.

Filling

There are a few common methods for filling the mold cavity: gravity, low-pressure, high-pressure, and vacuum.

Vacuum filling, also known as counter-gravity filling, is more metal efficient than gravity pouring because less material solidifies in the gating system. Gravity pouring only has a 15 to 50% metal yield as compared to 60 to 95% for vacuum pouring. There is also less turbulence, so the gating system can be simplified since it does not have to control turbulence. Plus, because the metal is drawn from below the top of the pool the metal is free from dross and slag, as these are lower density (lighter) and float to the top of the pool. The pressure differential helps the metal flow into every intricacy of the mold. Finally, lower temperatures can be used, which improves the grain structure. The first patented vacuum casting machine and process dates to 1879.

Low-pressure filling uses 5 to 15 psig (35 to 100 kPag) of air pressure to force liquid metal up a feed tube into the mold cavity. This eliminates turbulence found in gravity casting and increases density, repeatability, tolerances, and grain uniformity. After the casting has solidified the pressure is released and any remaining liquid returns to the crucible, which increases yield.

Tilt filling
Tilt filling, also known as tilt casting, is an uncommon filling technique where the crucible is attached to the gating system and both are slowly rotated so that the metal enters the mold cavity with little turbulence. The goal is to reduce porosity and inclusions by limiting turbulence. For most uses tilt filling is not feasible because the following inherent problem: if the system is rotated slow enough to not induce turbulence, the front of the metal stream begins to solidify, which results in mis-runs. If the system is rotated faster it induces turbulence, which defeats the purpose. Durville of France was the first to try tilt casting, in the 1800s. He tried to use it to reduce surface defects when casting coinage from aluminium bronze.

Macrostructure
The grain macrostructure in ingots and most castings have three distinct regions or zones: the chill zone, columnar zone, and equiaxed zone. The image below depicts these zones.

The chill zone is named so because it occurs at the walls of the mold where the wall chills the material. Here is where the nucleation phase of the solidification process takes place. As more heat is removed the grains grow towards the center of the casting. These are thin, long columns that are perpendicular to the casting surface, which are undesirable because they have anisotropic properties. Finally, in the center the equiaxed zone contains spherical, randomly oriented crystals. These are desirable because they have isotropic properties. The creation of this zone can be promoted by using a low pouring temperature, alloy inclusions, or inoculants.

Inspection
Common inspection methods for steel castings are magnetic particle testing and liquid penetrant testing. Common inspection methods for aluminum castings are radiography, ultrasonic testing, and liquid penetrant testing.

Defects
There are a number of problems that can be encountered during the casting process. The main types are: gas porosity, shrinkage defects, mold material defects, pouring metal defects, and metallurgical defects.

Casting process simulation
Casting processes simulation uses numerical methods to calculate cast component quality considering mold filling, solidification and cooling, and provides a quantitative prediction of casting mechanical properties, thermal stresses and distortion. Simulation accurately describes a cast component's quality up-front before production starts. The casting rigging can be designed with respect to the required component properties. This has benefits beyond a reduction in pre-production sampling, as the precise layout of the complete casting system also leads to energy, material, and tooling savings.

The software supports the user in component design, the determination of melting practice and casting methoding through to pattern and mold making, heat treatment, and finishing. This saves costs along the entire casting manufacturing route.

Casting process simulation was initially developed at universities starting from the early 1970s, mainly in Europe and in the U.S., and is regarded as the most important innovation in casting technology over the last 50 years. Since the late 1980s, commercial programs are available which make it possible for foundries to gain new insight into what is happening inside the mold or die during the casting process.

title: Metal casting


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Luke Skywalker

Luke Skywalker is a fictional character in the Star Wars franchise. He was introduced in the original film trilogy and also appears in the sequel trilogy. Raised as a moisture farmer on the planet Tatooine, Luke joins the Rebel Alliance and becomes a pivotal figure in the struggle against the Galactic Empire. He trains as a Jedi under Obi-Wan Kenobi and Yoda, and eventually confronts his father, the Sith Lord Darth Vader. Years later, Luke trains his nephew Ben Solo and mentors the scavenger Rey. Luke is the twin brother of Leia Organa.

Mark Hamill portrays Luke in all the films of the original trilogy and the sequel trilogy, and in the television series The Mandalorian and The Book of Boba Fett. Hamill won the Saturn Award for Best Actor for his portrayal of Luke in The Empire Strikes Back (1980), Return of the Jedi (1983) and The Last Jedi (2017). He was also nominated for the award for his performance in Star Wars (1977). Luke also appears in novels, comics, and video games.

Star Wars (1977)
George Lucas considered various characterizations for the protagonist of the original Star Wars film. The possibilities included a 60-year-old grizzled war hero, a Jedi Master, a dwarf, and a woman. Luke's original surname was "Starkiller", and it remained in the script until a few months into filming. It was dropped due to what Lucas called "unpleasant connotations" with Charles Manson, who became a "star killer" in 1969 when he murdered the well-known actress Sharon Tate. Lucas replaced the problematic name "Starkiller" with "Skywalker".

Return of the Jedi (1983)
An alternate ending to the film reportedly featured Luke disappearing into the wilderness "like Clint Eastwood in the spaghetti Westerns."

The Force Awakens (2015)
Luke's lack of screen time in The Force Awakens was due to concerns by screenwriter Michael Arndt that his presence would distract from Rey, leading to an agreement that he be removed from the screen and instead become a plot device. Hamill attended meetings for script readings, and helped conceal Luke's role in the film; instead of dialogue, he read stage directions. According to director and co-writer J. J. Abrams, this allowed Hamill to remain involved and his reading helped make a "better experience for everyone."

Portrayal
Mark Hamill was originally cast as Luke for Star Wars (1977). Other actors who auditioned for the role include Robby Benson, William Katt, Kurt Russell, and Charles Martin Smith. Hamill was injured in a car accident in January 1977, fracturing his nose and cheekbone. Lucas justified the slight change to Hamill's likeness this would impose upon the sequel film, The Empire Strikes Back (1980), by asserting that in the interim between the two films, Luke had been fighting for the Rebel Alliance. It was speculated that the wampa attack at the beginning of The Empire Strikes Back was written in to explain his facial injuries, but Lucas disputed this in the DVD commentary of the film.

Star Wars
Luke was introduced in Star Wars (1977), the first film of the original trilogy. He is portrayed by Mark Hamill in all three films of the trilogy. At the beginning of the film, Luke is living on a moisture farm on the desert planet Tatooine with his uncle Owen and aunt Beru. After his uncle purchases the droids C-3PO and R2-D2, Luke finds a message from Princess Leia of Alderaan inside R2-D2. When R2-D2 goes missing, Luke goes out to search for the droid, and is saved from Tusken Raiders by Obi-Wan Kenobi, an elderly hermit. R2-D2 plays the message from Leia, in which she asks Obi-Wan to help her defeat the Galactic Empire. Obi-Wan says that he and Luke's father were once Jedi Knights, and that Luke's father was murdered by a traitorous Jedi named Darth Vader. Obi-Wan presents Luke with his father's lightsaber and offers to take him to Alderaan and train him in the ways of the Force. Luke declines his offer, feeling obligated to his family's farm.

Luke changes his mind when he finds that Imperial stormtroopers have killed his aunt and uncle. He and Obi-Wan travel to Mos Eisley, where they meet the smugglers Han Solo and Chewbacca. They hire the duo to take them to Alderaan on the Millenium Falcon, only to discover that it has been destroyed by the Death Star, the Empire's battle station. The Falcon is brought to the Death Star via tractor beam, and Luke and Han disguise themselves as stormtroopers to infiltrate the station. When they discover Leia is being held captive, Luke persuades Han and Chewbacca to help rescue her. Obi-Wan deactivates the tractor beam, then sacrifices his life in a duel with Vader so the others can escape. Luke joins the Rebel Alliance and pilots an X-wing during the Battle of Yavin. He and other Rebels attempt to destroy the Death Star by launching torpedoes into an exhaust port. As he approaches the port, Luke hears Obi-Wan's voice, telling him to trust his feelings. He switches off his ship's missile guidance system, instead using the Force to guide the torpedoes. After destroying the Death Star, Luke receives a medal of honor from Leia.

The Empire Strikes Back
Luke returns in The Empire Strikes Back (1980). Three years after the destruction of the Death Star, Luke is now a commander in the Rebel Alliance. While on the ice planet Hoth, he is captured by a wampa, but manages to escape. Obi-Wan appears to him as a Force spirit and urges him to complete his training with the Jedi Master Yoda. When the Empire discovers the Rebel base, Luke leads a squadron of snowspeeders against the opposing AT-AT walkers, but is forced to retreat. After escaping in his X-wing, he travels to Dagobah and meets Yoda. He undergoes rigorous Jedi training, quickly expanding his Force abilities.

While on Dagobah, Luke has a vision of his friends in danger. Against the advice of both Obi-Wan and Yoda to stay and complete his training, he travels to Cloud City to help them, unwittingly falling into a trap set by Vader. He engages in a lightsaber duel with Vader, and is overpowered. After severing Luke's hand, Vader reveals that he is Luke's father, and invites him to join the dark side of the Force and rule the galaxy with him. Luke throws himself into a chasm, and finds himself on the underside of Cloud City. Hanging onto a slender rod, he uses the Force to contact Leia, who is leaving in the Falcon. She hears his plea, and Chewbacca turns the ship around to rescue him. After Luke returns to the Rebel fleet, his severed hand is replaced with a bio-mechanical one.

Return of the Jedi
A year later, Luke is a Jedi Knight and has constructed his own lightsaber. At the beginning of Return of the Jedi (1983), he returns to Tatooine with Leia, Chewbacca and Lando Calrissian to rescue Han, who was frozen in carbonite and delivered to the crime lord Jabba the Hutt. Luke offers to negotiate with Jabba, who rejects his offer and imprisons him with a giant beast called a rancor. When Luke kills the rancor, Jabba decides to execute him, Han and Chewbacca by casting them into a Sarlacc pit. Luke escapes with R2-D2's help, saving his friends and destroying Jabba's sail barge. Luke returns to Dagobah, where he learns from a dying Yoda that Vader is indeed his father. Luke is then informed by Obi-Wan's spirit that he has a twin sister, whom he realizes is Leia. Both Yoda and Obi-Wan tell Luke that he must face Vader again to finish his training and save the galaxy, but he is disturbed by the idea of killing his father.

While his companions undertake a mission on Endor, Luke surrenders to Vader in an attempt to bring him back from the dark side. Vader takes his son to the second Death Star and brings him before the Emperor, who attempts to seduce him to the dark side. Luke lashes out at the Emperor with his lightsaber, but Vader blocks his strike, and the two of them duel once again. As Luke regains control of his emotions, Vader senses that he has a sister, and threatens to turn her to the dark side if Luke will not submit. Enraged, Luke overpowers Vader and severs his hand. The Emperor then orders Luke to kill Vader and take his place, but Luke refuses. The Emperor begins torturing Luke with Force lightning, and Luke calls out to his father for help. Vader hesitates, then throws the Emperor down a reactor shaft to his death. Mortally wounded, Vader asks his son to remove his mask, which allows Luke to look upon the face of Anakin Skywalker for the first time. On Endor, Luke burns his father's body on a funeral pyre. As the Rebels celebrate the destruction of the Death Star and the fall of the Empire, Luke sees Anakin's spirit appear alongside the spirits of Obi-Wan and Yoda.

Revenge of the Sith
In the prequel film Revenge of the Sith (2005), Padmé Amidala gives birth to the twins Luke and Leia and then dies. and Yoda agree to separate the twins in order to protect them from their father, Vader, and the newly-created Galactic Empire. takes Luke to the desert planet Tatooine, where he is adopted by Vader's stepbrother, Owen Lars, and his wife Beru. Leia is adopted by Senator Bail Organa of Alderaan. Both infants are portrayed by Aidan Barton, the son of Roger Barton, an editor of the film.

Sequel trilogy
The first film of the sequel trilogy, The Force Awakens (2015), occurs thirty years after the destruction of the second Death Star. Hamill reprises his role as Luke in all three films. The opening crawl of The Force Awakens reveals that Luke disappeared after his nephew and Jedi apprentice, Ben Solo, turned to the dark side and became Kylo Ren, a warlord of the First Order. The Resistance, led by Leia, manage to locate Luke on the planet Ahch-To; the Force-sensitive scavenger Rey then travels to the planet and offers him his lightsaber. At the beginning of The Last Jedi (2017), Luke tosses the lightsaber aside. He refuses to talk to Rey, but eventually inquires about his family. Rey tells him about Han Solo's death at the hands of his son Ren, and explains that the First Order now rules the galaxy. She asks Luke to train her in the ways of the Force, but he is reluctant. He tells her it is time for the Jedi Order to end.Luke eventually begins instructing Rey, but is afraid of her power. He tells her the history of the Jedi Order, and how Darth Sidious rose to power. He claims the Jedi were partly responsible for his father's fall to the dark side. Luke admits that he briefly considered killing his nephew after seeing a vision of the destruction he could cause; when Ben woke to see Luke with his lightsaber drawn, he felt betrayed and left his training. Rey urges Luke to help her redeem Ben, but he refuses. When Rey leaves, Luke tries to burn the Jedi temple, but fails. He is then visited by the spirit of Yoda, who assures him that he still has a purpose. Later, Luke appears on Crait, where the Resistance is besieged. He apologizes to Leia for allowing Ben to fall to the dark side, then steps in front of the First Order forces. He survives an onslaught of blaster fire, then engages Ren in lightsaber combat. Ren seemingly cuts through him, but Luke is unharmed; he is still on Ahch-To, having used the Force to project himself to Crait. He then collapses and becomes one with the Force. His battle with Ren gave the Resistance time to escape the planet.

Luke returns in the final film of the trilogy, The Rise of Skywalker (2019). After Rey defeats Ren in a lightsaber duel, she flies his TIE fighter to Ahch-To, then burns the ship. When she throws Luke's lightsaber into the flames, he appears as a Force spirit and catches it. He reprimands her for treating the weapon with disrespect, and admits he was wrong not to participate in the Resistance. He thanks Rey for helping him rediscover himself, and urges her to continue her battle against the Sith. He gives her Leia's lightsaber and his X-wing for her journey to Exegol. After Rey vanquishes Palpatine, she visits the moisture farm where Luke was raised. When a passerby asks Rey who she is, she notices the spirits of Luke and Leia nearby, and replies "Rey Skywalker."

Series
Hamill portrays Luke in "Chapter 16: The Rescue", the season two finale of the live-action series The Mandalorian. The Force-sensitive infant Grogu had contacted him in a previous episode, and Luke now arrives to collect him and begin his Jedi training. Luke also destroys a group of Dark Troopers that were threatening Grogu and his guardian, Din Djarin.

The series The Book of Boba Fett features Hamill as Luke in the episode "Chapter 6: From the Desert Comes a Stranger". While training Grogu, Luke helps him remember some of his past, including his home at the Jedi Temple on Coruscant and the events of the Great Jedi Purge. Soon after, Djarin sends Luke a gift for Grogu: beskar chain mail forged by the Armorer. Unsure whether Grogu is committed to the Jedi path, Luke decides to let the child choose his own destiny. He invites him to choose between the chain mail and a lightsaber that belonged to Yoda. In "Chapter 7: In The Name of Honor", it is revealed that Grogu chose the chain mail, which leads Luke to send him back to Djarin.

Luke appears in two episodes of the animated web series Forces of Destiny, voiced by Hamill. The episode "The Path Ahead" details his training with Yoda on Dagobah. In "Traps and Tribulations", he and Leia help the Ewoks stop a rampaging beast known as a Gorax. Grant Feely portrays Luke as a ten-year-old child in the series Obi-Wan Kenobi (2022).

Novels and comics
The 2015 novel Heir to the Jedi takes place between Star Wars and The Empire Strikes Back, and chronicles the adventures of Luke as he continues to battle the Empire with his Rebel companions. He grows close with Nakari Kelen, a fellow Rebel, and he begins to develop his Force abilities. The novel is written from the first-person perspective of Luke, and is only the second Star Wars novel to utilize this type of narrative voice. Luke is featured in the junior novel The Legends of Luke Skywalker, which was adapted as a manga. He also appears in the 2015 comic Star Wars, which is set between the films of the original trilogy. The 2022 novel Shadow of the Sith, which is set between Return of the Jedi and The Force Awakens, follows Luke and Lando Calrissian as they search for Exegol.

Other
Hamill provides Luke's voice in The Star Wars Holiday Special (1978) and in radio adaptations of Star Wars (1981) and The Empire Strikes Back (1983). Joshua Fardon voices Luke in the Return of the Jedi radio drama. Luke also appears in video games, in which he is voiced by a variety of different actors.

Star Wars Legends
Following the acquisition of Lucasfilm by The Walt Disney Company in 2012, most of the licensed Star Wars novels and comics produced between 1977 and 2014 were rebranded as Star Wars Legends and declared non-canon to the franchise. The Legends works comprise a separate narrative universe.

Novels
The novel The Truce at Bakura (1997) takes place one day after the Battle of Endor. Luke and his friend Wedge Antilles recover a message droid from the planet Bakura, which is being invaded by the Ssi-Ruuk. Luke turns back the army and meets Dev Sibwarra, a Force-sensitive human who had been captured by the Ssi-Ruuk. Sibwarra is eventually killed after turning against his captors. The Courtship of Princess Leia (1995) is set four years after the Battle of Endor. Luke travels to the planet Dathomir, where he encounters the Force-sensitive Witches of Dathomir. He discovers a prophecy stating that a Jedi will change the way of life on Dathomir, and he eventually realizes what the Force truly is. Luke destroys most of the Nightsisters—a group of witches—and their leader Gethzirion. He also terminates Zsinj, the galaxy's most powerful warlord. Luke recovers Jedi records left by Yoda roughly 400 years prior, then decides to start a new Jedi Academy.

In the Thrawn trilogy, Luke meets Mara Jade, the former Emperor's Hand who is bound by Palpatine's disembodied voice that repeatedly commands "You will kill Luke Skywalker". Although she was ready to terminate Luke to stop the voice, she keeps him alive so he can help her escape from danger. Despite her threats, Luke learns about the spell Mara is under and vows to free her from it. Later, Luke and Mara fight against Luke's clone, Luuke Skywalker, a creation of Joruus C'baoth. Mara destroys the clone and eliminates C'baoth with help from Leia. Mara's curse is then silenced.

Luke resigns his commission in the New Republic starfighter corps in the Jedi Academy trilogy. He turns his attention to his Jedi studies and begins to rebuild the Jedi Order in the Massassi Temple on Yavin 4, a decision some anti-Jedi politicians use against him. He is forced to contend with the spirit of the ancient Sith Lord Exar Kun, who lures one of his most powerful students, Kyp Durron, to the dark side. In the Hand of Thrawn Duology, Luke is a Jedi Master. He works again with Mara, who has gained knowledge of the Force since her training at Luke's Jedi Academy. Luke falls in love with her and they eventually marry. In Edge of Victory: Rebirth, they have a son whom they name Ben, after Obi-Wan's alias.

Luke creates a New Jedi Council in the New Jedi Order series. He envisions a conclave composed of Jedi, politicians and military officers. In Force Heretic: Remnant, he spearheads a mission to the Unknown Regions during the Yuuzhan Vong invasion to find the mysterious planet Zonama Sekot, which creates living starships. After the invaders are defeated, Luke leads the New Jedi Order on Denon, the temporary capital of the Galactic Alliance.

In The Swarm War, the Order moves to Ossus, the site of Jedi temples and libraries that were mostly destroyed 4,000 years prior. Upon the Killik's invasion of Chiss space and the transformation of most of the Myrkr mission survivors into Killik Joiners, Luke deduces that the Killik's collective mind is being unconsciously controlled by a hive called the Dark Nest. The hive, in turn, is controlled by a former Nightsister named Lomi Plo, who became the Unseen Queen through her ability to become invisible by exploiting the doubts of inferiors. One of the Myrkr survivors, Alema Rar, suggests to Luke that Mara may be responsible for the death of his mother. Luke almost believes the lie due to Mara's previous role as the Emperor's Hand. His doubts are assuaged when he discovers several hologram recordings hidden in R2-D2's memory. He sees his father Force-choking his mother on Mustafar, as well as his own birth and his mother's death. Luke defeats Lomi Plo in the final battle of the Swarm War, cutting her into four pieces.

In the Legacy of the Force series, a schism develops between Luke and his nephew, Jacen Solo. Already a powerful Jedi, Jacen has begun adopting radical interpretations of the Force, which causes a dramatic change in his personality and makes Luke afraid that he will fall to the dark side. During this time, Luke begins having visions of a dark figure destroying the galaxy and the Jedi. The situation worsens in Bloodlines, when Luke's son Ben becomes Jacen's apprentice. In Tempest, Luke determines that the figure from his visions is Lumiya, a former Emperor's Hand now known as the "Dark Lady of the Sith".

When Mara is murdered in Sacrifice, Lumiya convinces Luke that she killed her. They battle, and Luke saves Lumiya from falling to her death so that he can kill her himself. However, he later realizes that Lumiya could not have killed Mara. He breaks down over the death of his wife, knowing that her murderer is still at large. He does not realize that the killer is Jacen, who has taken the Sith name Darth Caedus. In Revelation, Ben proves that Jacen killed Mara, but Luke is reluctant to destroy Jacen, fearing that he or Ben may fall to the dark side in the process. The decision is taken out of his hands in Invincible, when Jaina kills Jacen in a lightsaber duel.

The Fate of the Jedi novels are set about forty years after the original Star Wars film. Now in his sixties, Luke is deposed from his position as Grand Master and exiled from Coruscant. He will be allowed to return if he can discover why Jacen fell to the dark side. Luke and Ben embark on a journey together, exploring dangerous and little-known parts of the galaxy. They learn about each other, about the Force, and about the great dangers threatening the Jedi. The love between them grows greater as they repeatedly save each other's lives.

The Matthew Stover novel Luke Skywalker and the Shadows of Mindor (2008) takes place shortly after Return of the Jedi and the novel Prophets of the Dark Side. Luke and the Rebel Alliance are attempting to stop Lord Shadowspawn and his "shadow stormtroopers", a struggle which culminates in the Battle of Mindor. Stover said Shadows of Mindor was meant to evoke Brian Daley's Han Solo novels, which are Stover's favorite Star Wars books.

Comics
Luke appears in the Marvel-published comic adaptations of the original trilogy, as well as an ongoing series that ran from 1977 to 1986. He also appears in numerous titles released by Dark Horse Comics, including Star Wars: Legacy. In this series, which takes place 125 years after the events of the original trilogy, Luke appears to his descendant Cade Skywalker as a Force spirit. He persuades Cade to once again become a Jedi in order to defeat Darth Krayt and his burgeoning Sith Empire.

Reception
In regards to Luke's portrayal in The Last Jedi, many fans expressed disappointment in how he was depicted "as a grumpy old man whose failures had driven him into hiding" and the actions the character takes in contributing to Kylo Ren's backstory, a stark departure in how Luke was characterized in the original trilogy. Hamill originally stated that he fundamentally disagreed with "every choice [The Last Jedi director Rian Johnson] made for this character," but that he had the utmost respect for Johnson and was willing to do his part to realize Johnson's vision.

title: Luke Skywalker


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Double star

In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

This occurs because the pair either forms a binary star (i.e. a binary system of stars in mutual orbit, gravitationally bound to each other) or is an optical double, a chance line-of-sight alignment of two stars at different distances from the observer. Binary stars are important to stellar astronomers as knowledge of their motions allows direct calculation of stellar mass and other stellar parameters. The only (possible) case of "binary star" whose two components are separately visible to the naked eye is the case of Mizar and Alcor (though actually a multiple-star system), but it is not known for certain whether Mizar and Alcor are gravitationally bound.

Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs. If the relative motion of a pair determines a curved arc of an orbit, or if the relative motion is small compared to the common proper motion of both stars, it may be concluded that the pair is in mutual orbit as a binary star. Otherwise, the pair is optical. Multiple stars are also studied in this way, although the dynamics of multiple stellar systems are more complex than those of binary stars.

The following are three types of paired stars:
 * Optical doubles are unrelated stars that appear close together through chance alignment with Earth.
 * Visual binaries are gravitationally bound stars that are separately visible with a telescope.
 * Non-visual binaries are stars whose binary status was deduced through more esoteric means, such as occultation (eclipsing binaries), spectroscopy (spectroscopic binaries), or anomalies in proper motion (astrometric binaries).

Improvements in telescopes can shift previously non-visual binaries into visual binaries, as happened with Polaris A in 2006. It is only the inability to telescopically observe two separate stars that distinguishes non-visual and visual binaries.

History
Mizar, in Ursa Major, was observed to be double by Benedetto Castelli and Galileo. The identification of other doubles soon followed: Robert Hooke discovered one of the first double-star systems, Gamma Arietis, in 1664, while the bright southern star Acrux, in the Southern Cross, was discovered to be double by Fontenay in 1685. Since that time, the search has been carried out thoroughly and the entire sky has been examined for double stars down to a limiting apparent magnitude of about 9.0. At least 1 in 18 stars brighter than 9.0 magnitude in the northern half of the sky are known to be double stars visible with a 36 in telescope.

The unrelated categories of optical doubles and true binaries are lumped together for historical and practical reasons. When Mizar was found to be a binary, it was quite difficult to determine whether a double star was a binary system or only an optical double. Improved telescopes, spectroscopy, and photography are the basic tools used to make the distinction. After it was determined to be a visual binary, Mizar's components were found to be spectroscopic binaries themselves.

Observation of double stars

Observation of visual double stars by visual measurement will yield the separation, or angular distance, between the two component stars in the sky and the position angle. The position angle specifies the direction in which the stars are separated and is defined as the bearing from the brighter component to the fainter, where north is 0°. These measurements are called measures. In the measures of a visual binary, the position angle will change progressively and the separation between the two stars will oscillate between maximum and minimum values. Plotting the measures in the plane will produce an ellipse. This is the apparent orbit, the projection of the orbit of the two stars onto the celestial sphere; the true orbit can be computed from it. Although it is expected that the majority of catalogued visual doubles are visual binaries, orbits have been computed for only a few thousand of the over 100,000 known visual double stars.

Distinction between binary stars and other double stars
Confirmation of a visual double star as a binary star can be achieved by observing the relative motion of the components. If the motion is part of an orbit, or if the stars have similar radial velocities or the difference in their proper motions is small compared to their common proper motion, the pair is probably physical. When observed over a short period of time, the components of both optical doubles and long-period visual binaries will appear to be moving in straight lines; for this reason, it can be difficult to distinguish between these two possibilities.

Designations
Some bright visual double stars have a Bayer designation. In this case, the components may be denoted by superscripts. An example of this is α Crucis (Acrux), whose components are α1 Crucis and α2 Crucis. Since α1 Crucis is a spectroscopic binary, this is actually a multiple star. Superscripts are also used to distinguish more distant, physically unrelated, pairs of stars with the same Bayer designation, such as α1,2 Capricorni, ξ1,2 Centauri, and ξ1,2 Sagittarii. These optical pairs are resolvable by the naked eye.

Apart from these pairs, the components of a double star are generally denoted by the letters A (for the brighter, primary, star) and B (for the fainter, secondary, star) appended to the designation, of whatever sort, of the double star. For example, the components of α Canis Majoris (Sirius) are α Canis Majoris A and α Canis Majoris B (Sirius A and Sirius B); the components of 44 Boötis are 44 Boötis A and 44 Boötis B; the components of ADS 16402 are ADS 16402A and ADS 16402B; and so on. The letters AB may be used together to designate the pair. In the case of multiple stars, the letters C, D, and so on may be used to denote additional components, often in order of increasing separation from the brightest star, A.

Visual doubles are also designated by an abbreviation for the name of their discoverer followed by a catalogue number unique to that observer. For example, the pair α Centauri AB was discovered by Father Richaud in 1689, and so is designated RHD 1. Other examples include Δ65, the 65th double discovered by James Dunlop, and Σ2451, discovered by F. G. W. Struve.

The Washington Double Star Catalog, a large database of double and multiple stars, contains over 100,000 entries, each of which gives measures for the separation of two components. Each double star forms one entry in the catalog; multiple stars with n components will be represented by entries in the catalog for n−1 pairs, each giving the separation of one component of the multiple star from another. Codes such as AC are used to denote which components are being measured—in this case, component C relative to component A. This may be altered to a form such as AB-D to indicate the separation of a component from a close pair of components (in this case, component D relative to the pair AB.) Codes such as Aa may also be used to denote a component which is being measured relative to another component, A in this case. Discoverer designations are also listed; however, traditional discoverer abbreviations such as Δ and Σ have been encoded into a string of uppercase Roman letters, so that, for example, Δ65 has become DUN 65 and Σ2451 has become STF 2451. Further examples of this are shown in the adjacent table.

Visual binaries

 * Acrux
 * Capella
 * p Eridani
 * Polaris
 * Procyon
 * Sirius
 * Alpha Centauri system (AB) and Proxima Centauri (thus α Cen C): Actually a three-star system

Optical doubles

 * Alpha1 and Alpha2 Capricorni
 * Theta Muscae and Theta Muscae B
 * Eta1 and Eta2 Coronae Australis
 * Kappa1 and Kappa2 Coronae Australis
 * Winnecke 4 (Messier 40)
 * Polaris and Gamma Cephei, twin polar stars; Precession predicts Gamma Cephei should return to prominence by the year 3000.

Uncertain

 * Castor system (Aa/Ab/Ba/Bb) and YY Geminorum (thus Castor Ca/Cb) is generally considered a physical system
 * Mizar system (Aa/Ab/Ba/Bb) and Alcor (itself a binary, thus Mizar Ca/Cb, though generally not considered physical until 2009)

title: Double star