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Monday, October 18, 2021

The Lord of the Rings

From Wikipedia, the free encyclopedia

*The Lord of the Rings*
The first single-volume edition (1968)
Author	J. R. R. Tolkien
Country	England
Language	English
Genre	High fantasy Adventure
Publisher	Allen & Unwin
Publication date	29 July 1954 (The Fellowship of the Ring) 11 November 1954 (The Two Towers) 20 October 1955 (The Return of the King)
Media type	Print (hardback & paperback)
OCLC	1487587
Preceded by	The Hobbit
Followed by	The Adventures of Tom Bombadil

The Lord of the Rings is an epic high-fantasy novel by English author and scholar J. R. R. Tolkien. Set in Middle-earth, intended to be Earth at some distant time in the past, the story began as a sequel to Tolkien's 1937 children's book The Hobbit, but eventually developed into a much larger work. Written in stages between 1937 and 1949, The Lord of the Rings is one of the best-selling books ever written, with over 150 million copies sold.

The title refers to the story's main antagonist, the Dark Lord Sauron, who in an earlier age created the One Ring to rule the other Rings of Power given to Men, Dwarves, and Elves, in his campaign to conquer all of Middle-earth. From homely beginnings in the Shire, a hobbit land reminiscent of the English countryside, the story ranges across Middle-earth, following the quest to destroy the One Ring mainly through the eyes of the hobbits Frodo, Sam, Merry and Pippin.

Although often called a trilogy, the work was intended by Tolkien to be one volume of a two-volume set along with The Silmarillion. For economic reasons, The Lord of the Rings was published over the course of a year from 29 July 1954 to 20 October 1955, in three volumes titled The Fellowship of the Ring, The Two Towers, and The Return of the King. The work is divided internally into six books, two per volume, with several appendices of background material. Some later editions print the entire work in a single volume, following the author's original intent.

Tolkien's work, after an initially mixed reception by the literary establishment, has been the subject of extensive analysis of its themes and origins. Influences on this earlier work, and on the story of The Lord of the Rings, include philology, mythology, Christianity, earlier fantasy works, and his own experiences in the First World War.

The Lord of the Rings has since been reprinted many times and translated into at least 38 languages. The enduring popularity of The Lord of the Rings has led to numerous references in popular culture, the founding of many societies by fans of Tolkien's works, and the publication of many books about Tolkien and his works. It has inspired numerous derivative works, including artwork, music, films, television, video games, and board games, helping create and shape the modern fantasy genre, within which it is considered one of the greatest books of all time.

Award-winning adaptations of The Lord of the Rings have been made for radio, theatre, and film. It has been named Britain's best novel of all time in the BBC's The Big Read.

Plot

The Fellowship of the Ring

Prologue

The prologue explains that the book is "largely concerned with hobbits", telling of their origins in a migration from the east, their habits such as smoking "pipe-weed", and of how their homeland the Shire is organised. It explains how the narrative follows on from The Hobbit, in which the hobbit Bilbo Baggins finds the One Ring, which had been in the possession of Gollum.

Book One

Gandalf proves that Frodo's Ring is the One Ring by throwing it into Frodo's fireplace, revealing the hidden text of the Rhyme of the Rings.

Bilbo celebrates his 111th birthday and leaves the Shire suddenly, leaving the Ring to Frodo Baggins, his cousin and heir. Neither hobbit is aware of the Ring's origin, but the wizard Gandalf suspects it is a Ring of Power. Seventeen years later, Gandalf tells Frodo that he has confirmed that the Ring is the one lost by the Dark Lord Sauron long ago and counsels him to take it away from the Shire. Gandalf leaves, promising to return by Frodo's birthday and accompany him on his journey, but fails to do so.

Frodo sets out on foot, offering a cover story of moving to Crickhollow, accompanied by his gardener Sam Gamgee, and his cousin Pippin Took. They are pursued by mysterious Black Riders, but meet a passing group of Elves led by Gildor Inglorion, their chants to Elbereth ward off the Riders. The hobbits spend the night with them, then take an evasive short cut the next day, and arrive at the farm of Farmer Maggot, who takes them to Bucklebury Ferry, where they meet their friend Merry Brandybuck. When they reach the house at Crickhollow, Merry and Pippin reveal they know about the Ring and insist on travelling with Frodo and Sam.

They decide to try to shake off the Black Riders by cutting through the Old Forest. Merry and Pippin are trapped by Old Man Willow, an ancient tree who controls much of the forest, but are rescued by Tom Bombadil. Leaving the refuge of Tom's house, they get lost in a fog and are caught by a barrow-wight in a barrow on the downs, but Frodo, awakening from the barrow-wight's spell, calls Bombadil, who frees them, and equips them with ancient swords from the barrow-wight's hoard.

The hobbits reach the village of Bree, where they encounter a Ranger named Strider. The innkeeper gives Frodo a letter from Gandalf written three months before which identifies Strider as a friend. Strider leads the hobbits through the wilderness toward the Elven sanctuary of Rivendell. On the hill of Weathertop, they are again attacked by five of the nine Black Riders, whom Strider identifies as the Nazgûl, men of ancient times enslaved by lesser Rings of Power to serve Sauron. The Lord of the Nazgûl wounds Frodo with a cursed blade. After fighting off the Nazgûl, Strider treats Frodo with the herb athelas, and leads the hobbits towards Rivendell, but Frodo falls more and more deathly ill. The Nazgûl nearly capture Frodo at the Ford of Bruinen, but Strider and the Elf-lord Glorfindel drive the Nazgûl into the water, where flood waters summoned by Elrond, master of Rivendell, rise up and overwhelm them.

Book Two

Frodo recovers in Rivendell under Elrond's care. The Council of Elrond discusses the history of Sauron and the Ring. Strider is revealed to be Aragorn, the heir of Isildur. Isildur had cut the One Ring from Sauron's hand in the battle ending the Second Age, but refused to destroy it, claiming it for himself. The Ring had been lost when Isildur was killed, finally ending up in Bilbo's possession, after his meeting with Gollum, described in The Hobbit. Gandalf reports that the chief wizard, Saruman, has betrayed them and is now working to become a power in his own right. Gandalf was captured by Saruman, but escaped, explaining why he had failed to return to meet Frodo as he had promised.

The Council decides that the Ring must be destroyed, but that can only be done by sending it to the fire of Mount Doom in Mordor, where it was forged. Frodo takes this task upon himself. Elrond, with the advice of Gandalf, chooses companions for him. The Fellowship of the Ring consists of nine walkers to oppose the nine Black Riders: Frodo, Sam, Merry, Pippin, Aragorn, Gandalf, Gimli the Dwarf, Legolas the Elf, and Boromir, son of Denethor, the Steward of Gondor.

After a failed attempt to cross the Misty Mountains over the Redhorn Pass, the Fellowship take the perilous path through the Mines of Moria. They learn that Balin, one of the Dwarves who accompanied Bilbo in The Hobbit, and his colony of Dwarves were killed by Orcs. After surviving an attack, they are pursued by Orcs and a Balrog, an ancient fire demon from a prior Age, created by Sauron's old master, Morgoth. Gandalf confronts the Balrog, and both of them fall into the abyss. The others escape and find refuge in the timeless Elven forest of Lothlórien, where they are counselled by the Lady Galadriel. Before they leave, Galadriel tests their loyalty, and gives them individual, magical, gifts to help them on their quest. She allows Frodo and Sam to look into her fountain, the Mirror of Galadriel, to see visions of the past, the present, and perhaps the future, and she refuses to take the Ring, knowing that it would master her.

Galadriel's husband Celeborn gives the Fellowship boats, elven cloaks, and waybread, and they travel down the River Anduin to the hill of Amon Hen. There, Boromir tries to take the Ring from Frodo, but immediately regrets it after Frodo puts on the Ring and disappears. Frodo chooses to go alone to Mordor, but Sam, guessing what he intends, intercepts him as he tries to take a boat across the river, and goes with him.

The Two Towers

Book Three

A party of large Orcs, Uruk-hai, sent by Saruman, and other Orcs sent by Sauron and led by Grishnákh, attack the Fellowship. Boromir tries to protect Merry and Pippin from the Orcs, but they kill him and capture the two hobbits. Aragorn, Gimli and Legolas decide to pursue the Orcs taking Merry and Pippin to Saruman. In the kingdom of Rohan, the Orcs are killed by Riders of Rohan, led by Éomer. Merry and Pippin escape into Fangorn Forest, where they are befriended by Treebeard, the oldest of the tree-like Ents. Aragorn, Gimli and Legolas track the hobbits to Fangorn. There they unexpectedly meet Gandalf.

Gandalf explains that he killed the Balrog. He was also killed in the fight, but was sent back to Middle-earth to complete his mission. He is clothed in white and is now Gandalf the White, for he has taken Saruman's place as the chief of the wizards. Gandalf assures his friends that Merry and Pippin are safe. Together they ride to Edoras, capital of Rohan. Gandalf frees Théoden, King of Rohan, from the influence of Saruman's spy Gríma Wormtongue. Théoden musters his fighting strength and rides with his men to the ancient fortress of Helm's Deep, while Gandalf departs to seek help from Treebeard.

Meanwhile, the Ents, roused by Merry and Pippin from their peaceful ways, attack and destroy Isengard, Saruman's stronghold, and flood it, trapping the wizard in the tower of Orthanc. Gandalf convinces Treebeard to send an army of Huorns to Théoden's aid. He brings an army of Rohirrim to Helm's Deep, and they defeat the Orcs, who flee into the forest of Huorns, never to be seen again. Gandalf, Theoden, Legolas, and Gimli ride to Isengard, and are surprised to find Merry and Pippin relaxing amidst the ruins. Gandalf offers Saruman a chance to turn away from evil. When Saruman refuses to listen, Gandalf strips him of his rank and most of his powers. After Saruman leaves, Wormtongue throws down a hard round object to try to kill Gandalf. Pippin picks it up; Gandalf swiftly takes it, but Pippin steals it in the night. It is revealed to be a palantír, a seeing-stone that Saruman used to speak with Sauron, and that Sauron used to ensnare him. Pippin is seen by Sauron, but Sauron misunderstands the circumstances. Gandalf immediately rides for Minas Tirith, chief city of Gondor, taking Pippin with him.

Book Four

Frodo and Sam, heading for Mordor, struggle through the barren hills and cliffs of the Emyn Muil. They become aware they are being watched and tracked; on a moonlit night they capture Gollum, who has followed them from Moria. Frodo makes Gollum swear to serve him, as Ringbearer, and asks him to guide them to Mordor. Gollum leads them across the Dead Marshes. Sam overhears Gollum debating with his alter ego, Sméagol, whether to break his promise and steal the Ring.

They find that the Black Gate of Mordor is too well guarded, so instead they travel south through the land of Ithilien to a secret pass that Gollum knows. On the way, they are captured by rangers led by Faramir, Boromir's brother. He resists the temptation to seize the Ring and, disobeying standing orders to arrest strangers found in Ithilien, releases them.

Gollum–who is torn between his loyalty to Frodo and his desire for the Ring–guides the hobbits to the pass, but leads them into the lair of the great spider Shelob in the tunnels of Cirith Ungol. Frodo holds up the gift given to him in Lothlorien: the Phial of Galadriel, which holds the light of Eärendil's star. The light drives Shelob back. Frodo cuts through a giant web using his sword Sting. Shelob attacks again, and Frodo falls to her venom. Sam picks up Sting and the Phial. He seriously wounds and drives off the monster. Believing Frodo to be dead, Sam takes the Ring to continue the quest alone. Orcs find Frodo; Sam overhears them and learns that Frodo is still alive.

The Return of the King

Book Five

Sauron sends a great army against Gondor. Gandalf arrives at Minas Tirith to warn Denethor of the attack, while Théoden musters the Rohirrim to ride to Gondor's aid. Minas Tirith is besieged; the Lord of the Nazgûl uses a battering ram and the power of his Ring to destroy the city's gates. Denethor, deceived by Sauron, falls into despair. He burns himself alive on a pyre; Pippin and Gandalf rescue his son Faramir from the same fate.

Aragorn, accompanied by Legolas, Gimli, and the Rangers of the North, takes the Paths of the Dead to recruit the Dead Men of Dunharrow, oathbreakers who are bound by an ancient curse which denies them rest until they fulfil their oath to fight for the King of Gondor. Aragorn unleashes the Army of the Dead on the Corsairs of Umbar invading southern Gondor. With that threat eliminated, Aragorn uses the Corsairs' ships to transport the men of southern Gondor up the Anduin, reaching Minas Tirith just in time to turn the tide of battle. Théoden's niece Éowyn, who joined the army in disguise, kills the Lord of the Nazgûl with help from Merry; both are wounded. Together, Gondor and Rohan defeat Sauron's army in the Battle of the Pelennor Fields, though at great cost; Théoden is among the dead.

Aragorn enters Minas Tirith and heals Faramir, Eowyn, and Merry. He leads an army of men from Gondor and Rohan, marching through Ithilien to the Black Gate to distract Sauron from his true danger. At the Battle of the Morannon, his army is vastly outnumbered.

Book Six

Meanwhile, Sam rescues Frodo from the tower of Cirith Ungol. They set out across Mordor. When they reach the edge of the Cracks of Doom, Frodo cannot resist the Ring any longer. He claims it for himself and puts it on. Gollum suddenly reappears. He struggles with Frodo and bites off Frodo's finger with the Ring still on it. Celebrating wildly, Gollum loses his footing and falls into the Fire, taking the Ring with him. When the Ring is destroyed, Sauron loses his power forever. All he created collapses, the Nazgûl perish, and his armies are thrown into such disarray that Aragorn's forces emerge victorious.

Aragorn is crowned King of Arnor and Gondor, and weds Arwen, daughter of Elrond. Théoden is buried and Éomer is crowned King of Rohan. His sister Éowyn is engaged to marry Faramir, now Steward of Gondor and Prince of Ithilien. Galadriel, Celeborn, and Gandalf meet and say farewell to Treebeard, and to Aragorn.

The four hobbits make their way back to the Shire, only to find that it has been taken over by men directed by "Sharkey" (whom they later discover to be Saruman). The hobbits, led by Merry, raise a rebellion and scour the Shire of Sharkey's evil. Gríma Wormtongue turns on Saruman and kills him in front of Bag End, Frodo's home. He is killed in turn by hobbit archers. Merry and Pippin are celebrated as heroes. Sam marries Rosie Cotton and uses his gifts from Galadriel to help heal the Shire. But Frodo is still wounded in body and spirit, having borne the Ring for so long. A few years later, in the company of Bilbo and Gandalf, Frodo sails from the Grey Havens west over the Sea to the Undying Lands to find peace.

Appendices

The appendices outline more details of the history, cultures, genealogies, and languages Tolkien imagined for the peoples of Middle-earth. They provide background details for the narrative, and serve as "a gold mine" for Tolkien fans interested in understanding the fine detail in the stories.

Appendix A: "Annals of the Kings and Rulers": Provides extensive background to the larger world of Middle-earth, with brief overviews of the events of the first two Ages of the world, and then more detailed histories of the nations of Men in Gondor and Rohan, as well as a history of the royal Dwarvish line of Durin during the Third Age.

The embedded "Tale of Aragorn and Arwen" tells how it happened that an immortal elf came to marry a man, as told in the main story, which Arwen's ancestor Lúthien had done in the First Age, giving up her immortality.

Appendix B: "The Tale of Years" (Chronology of the Westlands): Is a timeline of events throughout the series, and ancient events affecting the narrative, and in lesser detail, they give the stories' context in the fictional chronology of the larger mythology.

It also tells that Sam gives his daughter Elanor the fictional Red Book of Westmarch – which contains the autobiographical stories of Bilbo's adventures at the opening of the war, and Frodo's role in the full-on War of the Ring, and serves as Tolkien's source for The Hobbit and The Lord of the Rings (with Tolkien representing himself as a translator, rather than an epic novelist). It says that there was "a tradition" that after handing over the book, Sam crossed west over the sea himself, the last of the ring-bearers; and that some years later, after the deaths of Aragorn and Arwen, Legolas and Gimli also sailed together "over Sea".

Appendix C: "Family Trees" (Hobbits): Gives hobbit genealogies – not only for Bilbo and Frodo's Baggins family, but also their relations the Tooks and Brandybucks, which connect them to Pippin and Merry.

Appendix D: "Calendars": Describes some of the calendars used by the characters in the story, and explains that the Roman month names in the text are "translations" of the names in the hobbits' calendar. (Tolkien was a linguist, and provided Germanic-sounding names for the hobbit calendar by extrapolating names of German and Old English months forward to what he thought they might have become if all were still used in modern English, as Yule and Easter are.)

Appendix E: "Writing and Spelling": Describes dwarves’ runes and the elvish runes use by the other peoples of Middle-earth; the names of the runes and letters incidentally give a bit of information about dwarvish and elvish languages.

Appendix F: "Languages and Peoples of the Third Age" and "On Translation": Presented as two sections. In addition to outlines of the various languages in current use during the narrative, and mentioned or seen in the story, it discusses hobbits' names at length. It sorts out names which Tolkien affected to have translated into English, and names which said he had left in original form (since they had no meaning in hobbits' everyday language).

Frame story

Tolkien presents The Lord of the Rings within a fictional frame story where he is not the original author, but merely the translator of part of an ancient document, the Red Book of Westmarch. That book is modelled on the real Red Book of Hergest, which similarly presents an older mythology. Various details of the frame story appear in the Prologue, its "Note on Shire Records", and in the Appendices, notably Appendix F. In this frame story, the Red Book is the purported source of Tolkien's other works relating to Middle-earth: The Hobbit, The Silmarillion, and The Adventures of Tom Bombadil.

Concept and creation

Background

Although a major work in itself, The Lord of the Rings was only the last movement of a much older set of narratives Tolkien had worked on since 1917 encompassing The Silmarillion, in a process he described as mythopoeia.

The Lord of the Rings started as a sequel to Tolkien's work The Hobbit, published in 1937. The popularity of The Hobbit had led George Allen & Unwin, the publishers, to request a sequel. Tolkien warned them that he wrote quite slowly, and responded with several stories he had already developed. Having rejected his contemporary drafts for The Silmarillion, putting Roverandom on hold, and accepting Farmer Giles of Ham, Allen & Unwin continued to ask for more stories about hobbits.

Writing

Persuaded by his publishers, he started "a new Hobbit" in December 1937. After several false starts, the story of the One Ring emerged. The idea for the first chapter ("A Long-Expected Party") arrived fully formed, although the reasons behind Bilbo's disappearance, the significance of the Ring, and the title The Lord of the Rings did not arrive until the spring of 1938. Originally, he planned to write a story in which Bilbo had used up all his treasure and was looking for another adventure to gain more; however, he remembered the Ring and its powers and thought that would be a better focus for the new work. As the story progressed, he brought in elements from The Silmarillion mythology.

Writing was slow, because Tolkien had a full-time academic position, marked exams to bring in a little extra income, and wrote many drafts. Tolkien abandoned The Lord of the Rings during most of 1943 and only restarted it in April 1944, as a serial for his son Christopher Tolkien, who was sent chapters as they were written while he was serving in South Africa with the Royal Air Force. Tolkien made another major effort in 1946, and showed the manuscript to his publishers in 1947. The story was effectively finished the next year, but Tolkien did not complete the revision of earlier parts of the work until 1949. The original manuscripts, which total 9,250 pages, now reside in the J. R. R. Tolkien Collection at Marquette University.

Poetry

Unusually for 20th century novels, the prose narrative is supplemented throughout by over 60 pieces of poetry. These include verse and songs of many genres: for wandering, marching to war, drinking, and having a bath; narrating ancient myths, riddles, prophecies, and magical incantations; and of praise and lament (elegy). Some, such as riddles, charms, elegies, and narrating heroic actions are found in Old English poetry. Scholars have stated that the poetry is essential for the fiction to work aesthetically and thematically, as it adds information not given in the prose, and it brings out characters and their backgrounds. The poetry has been judged to be of high technical skill, reflected in Tolkien's prose; for instance, he wrote much of Tom Bombadil's speech in metre.

Illustrations

Tolkien's calligraphy of the Rhyme of the Rings was one of the few illustrations in the first edition.

Tolkien worked on the text using his maps of Middle-earth as a guide, to ensure the elements of the story fitted together in time and space. He prepared a variety of types of illustration – maps, calligraphy, drawings, cover designs, even a facsimile painting of the Book of Mazarbul – but only the maps, the inscription on the Ring, and a drawing of the Doors of Durin were included in the first edition.

The hardback editions sometimes had cover illustrations by Tolkien, sometimes by other artists. According to The New York Times, Barbara Remington's cover designs for Ballantine's paperback editions "achieved mass-cult status in the 1960s, particularly on college campuses" across America. In the rush to print, Remington had no time to read the book, and surprised Tolkien with details such as a tree with pumpkin-like fruits, and a lion, which was painted out for later editions.

Influences

Beowulf's eotenas [ond] ylfe [ond] orcneas, "ogres [and] elves [and] devil-corpses" helped to inspire Tolkien to create the Orcs and Elves of Middle-earth.

Tolkien drew on a wide array of influences including language, Christianity, mythology and Germanic heroic legend including the Norse Völsunga saga, archaeology, especially at the Temple of Nodens, ancient and modern literature, and personal experience. He was inspired primarily by his profession, philology; his work centred on the study of Old English literature, especially Beowulf, and he acknowledged its importance to his writings. He was a gifted linguist, influenced by Celtic, Finnish, Slavic, and Greek language and mythology. Commentators have attempted to identify literary and topological antecedents for characters, places and events in Tolkien's writings; he acknowledged that he had enjoyed adventure stories by authors such as John Buchan and Rider Haggard. The Arts and Crafts polymath William Morris was a major influence, and Tolkien undoubtedly made use of some real place-names, such as Bag End, the name of his aunt's home. Tolkien stated, too, that he had been influenced by his childhood experiences of the English countryside of Worcestershire near Sarehole Mill, and its urbanisation by the growth of Birmingham,and his personal experience of fighting in the trenches of the First World War. Moreover, the militarization and industrialization inspired the character of Sauron and his forces. The Orcs represented the worst of it as workers that have been tortured and brutalized by the war and industry.

Themes

Scholars and critics have identified many themes in the book with its complex interlaced narrative, including a reversed quest, the struggle of good and evil, death and immortality, fate and free will, the addictive danger of power, and various aspects of Christianity such as the presence of three Christ figures, for prophet, priest, and king, as well as elements like hope and redemptive suffering. There is a common theme throughout the work of language, its sound, and its relationship to peoples and places, along with hints of providence in descriptions of weather and landscape. Out of these, Tolkien stated that the central theme is death and immortality. To those who supposed that the book was an allegory of events in the 20th century, Tolkien replied in the foreword to the Second Edition that it was not, saying he preferred "history, true or feigned, with its varied applicability to the thought and experience of readers."

Some commentators have accused the book of being a story about men for boys, with no significant women; or about a purely rural world with no bearing on modern life in cities; of containing no sign of religion; or of racism. All of these charges have been rebutted by other commentators, who note that there are three powerful women in the book, Galadriel, Éowyn, and Arwen; that life, even in rural Hobbiton, is not idealised; that Christianity is a pervasive theme; and that Tolkien was sharply anti-racist both in peacetime and during the Second World War, while Middle-earth is evidently polycultural.

Publication history

A dispute with his publisher, George Allen & Unwin, led to his offering the work to William Collins in 1950. Tolkien intended The Silmarillion (itself largely unrevised at this point) to be published along with The Lord of the Rings, but Allen & Unwin were unwilling to do this. After Milton Waldman, his contact at Collins, expressed the belief that The Lord of the Rings itself "urgently wanted cutting", Tolkien eventually demanded that they publish the book in 1952. Collins did not; and so Tolkien wrote to Allen and Unwin, saying, "I would gladly consider the publication of any part of the stuff", fearing his work would never see the light of day.

For publication, the work was divided into three volumes to minimize any potential financial loss due to the high cost of type-setting and modest anticipated sales: The Fellowship of the Ring (Books I and II), The Two Towers (Books III and IV), and The Return of the King (Books V and VI plus six appendices). Delays in producing appendices, maps and especially an index led to the volumes being published later than originally hoped – on 29 July 1954, on 11 November 1954 and on 20 October 1955 respectively in the United Kingdom. In the United States, Houghton Mifflin published The Fellowship of the Ring on 21 October 1954, The Two Towers on 21 April 1955, and The Return of the King on 5 January 1956.

The Return of the King was especially delayed as Tolkien revised the ending and prepared appendices (some of which had to be left out because of space constraints). Tolkien did not like the title The Return of the King, believing it gave away too much of the storyline, but deferred to his publisher's preference. Tolkien wrote that the title The Two Towers "can be left ambiguous," but considered naming the two as Orthanc and Barad-dûr, Minas Tirith and Barad-dûr, or Orthanc and the Tower of Cirith Ungol. However, a month later he wrote a note published at the end of The Fellowship of the Ring and later drew a cover illustration, both of which identified the pair as Minas Morgul and Orthanc.

Tolkien was initially opposed to titles being given to each two-book volume, preferring instead the use of book titles: e.g. The Lord of the Rings: Vol. 1, The Ring Sets Out and The Ring Goes South; Vol. 2, The Treason of Isengard and The Ring Goes East; Vol. 3, The War of the Ring and The End of the Third Age. However, these individual book titles were dropped, and after pressure from his publishers, Tolkien suggested the volume titles: Vol. 1, The Shadow Grows; Vol. 2, The Ring in the Shadow; Vol. 3, The War of the Ring or The Return of the King.

Because the three-volume binding was so widely distributed, the work is often referred to as the Lord of the Rings "trilogy". In a letter to the poet W. H. Auden, who famously reviewed the final volume in 1956, Tolkien himself made use of the term "trilogy" for the work though he did at other times consider this incorrect, as it was written and conceived as a single book. It is often called a novel; however, Tolkien objected to this term as he viewed it as a heroic romance.

The books were published under a profit-sharing arrangement, whereby Tolkien would not receive an advance or royalties until the books had broken even, after which he would take a large share of the profits. It has ultimately become one of the best-selling novels ever written, with 50 million copies sold by 2003 and over 150 million copies sold by 2007. The work was published in the UK by Allen & Unwin until 1990, when the publisher and its assets were acquired by HarperCollins.

Editions and revisions

In the early 1960s Donald A. Wollheim, science fiction editor of the paperback publisher Ace Books, claimed that The Lord of the Rings was not protected in the United States under American copyright law because Houghton Mifflin, the US hardcover publisher, had neglected to copyright the work in the United States. Then, in 1965, Ace Books proceeded to publish an edition, unauthorized by Tolkien and without paying royalties to him. Tolkien took issue with this and quickly notified his fans of this objection. Grass-roots pressure from these fans became so great that Ace Books withdrew their edition and made a nominal payment to Tolkien.

Barbara Remington's cover illustrations for the Ballantine paperback version "achieved mass-cult status" on American college campuses in the 1960s. They were parodied by Michael K. Frith's cover design for the 1969 Bored of the Rings.

Authorized editions followed from Ballantine Books and Houghton Mifflin to tremendous commercial success. Tolkien undertook various textual revisions to produce a version of the book that would be published with his consent and establish an unquestioned US copyright. This text became the Second Edition of The Lord of the Rings, published in 1965. The first Ballantine paperback edition was printed in October that year, selling a quarter of a million copies within ten months. On 4 September 1966, the novel debuted on The New York Times's Paperback Bestsellers list as number three, and was number one by 4 December, a position it held for eight weeks. Houghton Mifflin editions after 1994 consolidate variant revisions by Tolkien, and corrections supervised by Christopher Tolkien, which resulted, after some initial glitches, in a computer-based unified text.

In 2004, for the 50th Anniversary Edition, Wayne G. Hammond and Christina Scull, under supervision from Christopher Tolkien, studied and revised the text to eliminate as many errors and inconsistencies as possible, some of which had been introduced by well-meaning compositors of the first printing in 1954, and never been corrected. The 2005 edition of the book contained further corrections noticed by the editors and submitted by readers. Yet more corrections were made in the 60th Anniversary Edition in 2014. Several editions, including the 50th Anniversary Edition, print the whole work in one volume, with the result that pagination varies widely over the various editions.

Posthumous publication of drafts

From 1988 to 1992 Christopher Tolkien published the surviving drafts of The Lord of The Rings, chronicling and illuminating with commentary the stages of the text's development, in volumes 6–9 of his History of Middle-earth series. The four volumes carry the titles The Return of the Shadow, The Treason of Isengard, The War of the Ring, and Sauron Defeated.

Translations

The work has been translated, with varying degrees of success, into at least 38, and reportedly at least 70, languages. Tolkien, an expert in philology, examined many of these translations, and made comments on each that reflect both the translation process and his work. As he was unhappy with some choices made by early translators, such as the Swedish translation by Åke Ohlmarks, Tolkien wrote a "Guide to the Names in The Lord of the Rings" (1967). Because The Lord of the Rings purports to be a translation of the fictitious Red Book of Westmarch, using the English language to represent the Westron of the "original", Tolkien suggested that translators attempt to capture the interplay between English and the invented nomenclature of the English work, and gave several examples along with general guidance.

Reception

1950s

Early reviews for The Lord of the Rings were mixed. The initial review in the Sunday Telegraph described it as "among the greatest works of imaginative fiction of the twentieth century". The Sunday Times echoed this sentiment, stating that "the English-speaking world is divided into those who have read The Lord of the Rings and The Hobbit and those who are going to read them." The New York Herald Tribune appeared to predict the books' popularity, writing in its review that they were "destined to outlast our time". W. H. Auden, a former pupil of Tolkien's and an admirer of his writings, regarded The Lord of the Rings as a "masterpiece", further stating that in some cases it outdid the achievement of John Milton's Paradise Lost. Kenneth F. Slater wrote in Nebula Science Fiction, April 1955, "... if you don't read it, you have missed one of the finest books of its type ever to appear".

Even within Tolkien's literary group, The Inklings, the work had a mixed reception. Hugo Dyson complained loudly at its readings, whereas C. S. Lewis had very different feelings, writing, "here are beauties which pierce like swords or burn like cold iron. Here is a book which will break your heart." Lewis observed that the writing is rich, in that some of the 'good' characters have darker sides, and likewise some of the villains have "good impulses". Despite the mixed reviews and the lack of a paperback until the 1960s, The Lord of the Rings initially sold well in hardback.

Later

Judith Shulevitz, writing in The New York Times, criticized the "pedantry" of Tolkien's literary style, saying that he "formulated a high-minded belief in the importance of his mission as a literary preservationist, which turns out to be death to literature itself". The critic Richard Jenkyns, writing in The New Republic, criticized the work for a lack of psychological depth. Both the characters and the work itself were, according to Jenkyns, "anemic, and lacking in fibre". The science fiction author David Brin interprets the work as holding unquestioning devotion to a traditional hierarchical social structure. In his essay "Epic Pooh", fantasy author Michael Moorcock critiques the world-view displayed by the book as deeply conservative, in both the "paternalism" of the narrative voice and the power structures in the narrative. Tom Shippey, like Tolkien an English philologist, notes the wide gulf between Tolkien's supporters, both popular and academic, and his literary detractors, and attempts to explain in detail both why the literary establishment disliked The Lord of the Rings, and the work's subtlety, themes, and merits, including the impression of depth that it conveys. The scholar of humanities Brian Rosebury analysed Tolkien's prose style in detail, showing that it was generally quite plain, varying to suit the voices of the different characters, and rising to a heroic register for special moments.

Awards

In 1957, The Lord of the Rings was awarded the International Fantasy Award. Despite its numerous detractors, the publication of the Ace Books and Ballantine paperbacks helped The Lord of the Rings become immensely popular in the United States in the 1960s. The book has remained so ever since, ranking as one of the most popular works of fiction of the twentieth century, judged by both sales and reader surveys. In the 2003 "Big Read" survey conducted in Britain by the BBC, The Lord of the Rings was found to be the "Nation's best-loved book". In similar 2004 polls both Germany and Australia chose The Lord of the Rings as their favourite book. In a 1999 poll of Amazon.com customers, The Lord of the Rings was judged to be their favourite "book of the millennium". In 2019, the BBC News listed The Lord of the Rings on its list of the 100 most influential novels.

Adaptations

The Lord of the Rings has been adapted for radio, stage, film and television.

Radio

The book has been adapted for radio four times. In 1955 and 1956, the BBC broadcast The Lord of the Rings, a 13-part radio adaptation of the story. In the 1960s radio station WBAI produced a short radio adaptation. A 1979 dramatization of The Lord of the Rings was broadcast in the United States and subsequently issued on tape and CD. In 1981, the BBC broadcast The Lord of the Rings, a new dramatization in 26 half-hour instalments.

Film and television

A variety of filmmakers considered adapting Tolkien's book, among them Stanley Kubrick, who thought it unfilmable, Michelangelo Antonioni, Heinz Edelmann, and John Boorman. A Swedish live action television film, Sagan om ringen, was broadcast in 1971. In 1978, Ralph Bakshi made an animated film version covering The Fellowship of the Ring and part of The Two Towers, to mostly poor reviews. In 1980, Rankin/Bass released an animated TV special based on the closing chapters of The Return of the King, gaining mixed reviews. In Finland, a live action television miniseries, Hobitit, was broadcast in 1993 based on The Lord of the Rings, with a flashback to Bilbo's encounter with Gollum in The Hobbit.

A far more successful adaptation was Peter Jackson's live action The Lord of the Rings film trilogy, produced by New Line Cinema and released in three instalments as The Lord of the Rings: The Fellowship of the Ring (2001), The Lord of the Rings: The Two Towers (2002), and The Lord of the Rings: The Return of the King (2003). All three parts won multiple Academy Awards, including consecutive Best Picture nominations. The final instalment of this trilogy was the second film to break the one-billion-dollar barrier and won a total of 11 Oscars (something only two other films in history, Ben-Hur and Titanic, have accomplished), including Best Picture, Best Director and Best Adapted Screenplay. Commentators including Tolkien scholars, literary critics and film critics are divided on how faithfully Jackson adapted Tolkien's work, or whether a film version is inevitably different, and if so the reasons for any changes, and the effectiveness of the result.

The Hunt for Gollum, a 2009 film by Chris Bouchard, and the 2009 Born of Hope, written by Paula DiSante and directed by Kate Madison, are fan films based on details in the appendices of The Lord of the Rings.

In 2017, Amazon acquired the global television rights to The Lord of the Rings for a multi-season television series of new stories set before The Hobbit and The Lord of the Rings, based on Tolkien's descriptions of events of the Second Age of Middle-earth.

Stage

In 1990, Recorded Books published an audio version of The Lord of the Rings, read by the British actor Rob Inglis. A large-scale musical theatre adaptation, The Lord of the Rings, was first staged in Toronto, Ontario, Canada in 2006 and opened in London in June 2007; it was a commercial failure.

Legacy

Influence on fantasy

The enormous popularity of Tolkien's work expanded the demand for fantasy. Largely thanks to The Lord of the Rings, the genre flowered throughout the 1960s and enjoys popularity to the present day. The opus has spawned many imitations, such as The Sword of Shannara, which Lin Carter called "the single most cold-blooded, complete rip-off of another book that I have ever read," as well as alternate interpretations of the story, such as The Last Ringbearer. The Legend of Zelda, which popularized the action-adventure game genre in the 1980s, was inspired by The Lord of the Rings among other fantasy books. Dungeons & Dragons, which popularized the role-playing game genre in the 1970s, features several races from The Lord of the Rings, including halflings (hobbits), elves, dwarves, half-elves, orcs, and dragons. However, Gary Gygax, lead designer of the game, maintained that he was influenced very little by The Lord of the Rings, stating that he included these elements as a marketing move to draw on the popularity the work enjoyed at the time he was developing the game. Because Dungeons & Dragons has gone on to influence many popular role-playing video games, the influence of The Lord of the Rings extends to many of them, with titles such as Dragon Quest, the Ultima series, EverQuest, the Warcraft series, and The Elder Scrolls series of games as well as video games set in Middle-earth itself.

Music

In 1965, the songwriter Donald Swann, best known for his collaboration with Michael Flanders as Flanders & Swann, set six poems from The Lord of the Rings and one from The Adventures of Tom Bombadil ("Errantry") to music. When Swann met with Tolkien to play the songs for his approval, Tolkien suggested for "Namárië" (Galadriel's lament) a setting reminiscent of plain chant, which Swann accepted. The songs were published in 1967 as The Road Goes Ever On: A Song Cycle, and a recording of the songs performed by singer William Elvin with Swann on piano was issued that same year by Caedmon Records as Poems and Songs of Middle Earth.

Rock bands of the 1970s were musically and lyrically inspired by the fantasy-embracing counter-culture of the time. The British rock band Led Zeppelin recorded several songs that contain explicit references to The Lord of the Rings, such as mentioning Gollum and Mordor in "Ramble On", the Misty Mountains in "Misty Mountain Hop", and Ringwraiths in "The Battle of Evermore". In 1970, the Swedish musician Bo Hansson released an instrumental concept album entitled Sagan om ringen ("The Saga of the Ring", the title of the Swedish translation at the time). The album was subsequently released internationally as Music Inspired by Lord of the Rings in 1972. From the 1980s onwards, many heavy metal acts have been influenced by Tolkien.

In 1988, the Dutch composer and trombonist Johan de Meij completed his Symphony No. 1 "The Lord of the Rings". It had 5 movements, titled "Gandalf", "Lothlórien", "Gollum", "Journey in the Dark", and "Hobbits".

The 1991 album Shepherd Moons by the Irish musician Enya contains an instrumental titled "Lothlórien", in reference to the home of the wood-elves.

Impact on popular culture

"Welcome to Hobbiton" sign in Matamata, New Zealand, where Peter Jackson's film version was shot

The Lord of the Rings has had a profound and wide-ranging impact on popular culture, beginning with its publication in the 1950s, but especially during the 1960s and 1970s, when young people embraced it as a countercultural saga. "Frodo Lives!" and "Gandalf for President" were two phrases popular amongst United States Tolkien fans during this time. Its impact is such that the words "Tolkienian" and "Tolkienesque" have entered the Oxford English Dictionary, and many of his fantasy terms, formerly little-known in English, such as "Orc" and "Warg", have become widespread in that domain. Among its effects are numerous parodies, especially Harvard Lampoon's Bored of the Rings, which has had the distinction of remaining continuously in print from its publication in 1969, and of being translated into at least 11 languages.

In 1969, Tolkien sold the merchandising rights to The Lord of The Rings (and The Hobbit) to United Artists under an agreement stipulating a lump sum payment of £10,000 plus a 7.5% royalty after costs, payable to Allen & Unwin and the author. In 1976, three years after the author's death, United Artists sold the rights to Saul Zaentz Company, who now trade as Tolkien Enterprises. Since then all "authorised" merchandise has been signed off by Tolkien Enterprises, although the intellectual property rights of the specific likenesses of characters and other imagery from various adaptations is generally held by the adaptors.

Outside any commercial exploitation from adaptations, from the late 1960s onwards there has been an increasing variety of original licensed merchandise, with posters and calendars created by illustrators such as Barbara Remington.

The work was named Britain's best novel of all time in the BBC's The Big Read. In 2015, the BBC ranked The Lord of the Rings 26th on its list of the 100 greatest British novels. It was included in Le Monde's list of "100 Books of the Century".

Sunday, October 17, 2021

Earth's magnetic field

From Wikipedia, the free encyclopedia

Computer simulation of the Earth's field in a period of normal polarity between reversals. The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core.

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in the Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo. The magnitude of the Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 gauss). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11 degrees with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through the center of the Earth. The North geomagnetic pole actually represents the South pole of the Earth's magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward the Earth's South magnetic field, i.e., the North geomagnetic pole near the Geographic North Pole). As of 2015, the North geomagnetic pole was located on Ellesmere Island, Nunavut, Canada.

While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, the Earth's field reverses and the North and South Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.

The magnetosphere is the region above the ionosphere that is defined by the extent of the Earth's magnetic field in space. It extends several tens of thousands of kilometres into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from the harmful ultraviolet radiation.

Significance

Earth's magnetic field deflects most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.

The study of the past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth's magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetism to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores.

Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass can remain useful for navigation. Using magnetoreception, various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation.

Characteristics

At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination ( $D$ ) or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination ( $I$ ) or magnetic dip. The intensity ( $F$ ) of the field is proportional to the force it exerts on a magnet. Another common representation is in $X$ (North), $Y$ (East) and $Z$ (Down) coordinates.

Common coordinate systems used for representing the Earth's magnetic field.

Intensity

The intensity of the field is often measured in gauss (G), but is generally reported in nanoteslas (nT), with 1 G = 100,000 nT. A nanotesla is also referred to as a gamma (γ). The Earth's field ranges between approximately 25,000 and 65,000 nT (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field of about 10,000,000 nanoteslas (100 G).

A map of intensity contours is called an isodynamic chart. As the World Magnetic Model shows, the intensity tends to decrease from the poles to the equator. A minimum intensity occurs in the South Atlantic Anomaly over South America while there are maxima over northern Canada, Siberia, and the coast of Antarctica south of Australia.

The intensity of the magnetic field is subject to change over time. A 2021 paleomagnetic study from the University of Liverpool contributed to a growing body of evidence that the Earth's magnetic field cycles with intensity every 200 million years. The lead author stated that “Our findings, when considered alongside the existing datasets, support the existence of an approximately 200-million-year-long cycle in the strength of the Earth’s magnetic field related to deep Earth processes.”

Inclination

The inclination is given by an angle that can assume values between -90° (up) to 90° (down). In the northern hemisphere, the field points downwards. It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator. It continues to rotate upwards until it is straight up at the South Magnetic Pole. Inclination can be measured with a dip circle.

An isoclinic chart (map of inclination contours) for the Earth's magnetic field is shown below.

Declination

Declination is positive for an eastward deviation of the field relative to true north. It can be estimated by comparing the magnetic north–south heading on a compass with the direction of a celestial pole. Maps typically include information on the declination as an angle or a small diagram showing the relationship between magnetic north and true north. Information on declination for a region can be represented by a chart with isogonic lines (contour lines with each line representing a fixed declination).

Geographical variation

Components of the Earth's magnetic field at the surface from the World Magnetic Model for 2015.

Intensity
Inclination
Declination

Dipolar approximation

Relationship between Earth's poles. A1 and A2 are the geographic poles; B1 and B2 are the geomagnetic poles; C1 (south) and C2 (north) are the magnetic poles.

Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of the Earth and tilted at an angle of about 11° with respect to the rotational axis of the Earth. The dipole is roughly equivalent to a powerful bar magnet, with its south pole pointing towards the geomagnetic North Pole. This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations.

Magnetic poles

The movement of Earth's North Magnetic Pole across the Canadian arctic.

Historically, the north and south poles of a magnet were first defined by the Earth's magnetic field, not vice versa, since one of the first uses for a magnet was as a compass needle. A magnet's North pole is defined as the pole that is attracted by the Earth's North Magnetic Pole when the magnet is suspended so it can turn freely. Since opposite poles attract, the North Magnetic Pole of the Earth is really the south pole of its magnetic field (the place where the field is directed downward into the Earth).

The positions of the magnetic poles can be defined in at least two ways: locally or globally. The local definition is the point where the magnetic field is vertical. This can be determined by measuring the inclination. The inclination of the Earth's field is 90° (downwards) at the North Magnetic Pole and -90° (upwards) at the South Magnetic Pole. The two poles wander independently of each other and are not directly opposite each other on the globe. Movements of up to 40 kilometres (25 mi) per year have been observed for the North Magnetic Pole. Over the last 180 years, the North Magnetic Pole has been migrating northwestward, from Cape Adelaide in the Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001. The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal).

The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South geomagnetic poles. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either.

Magnetosphere

An artist's rendering of the structure of a magnetosphere. 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere.

Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF).

The solar wind exerts a pressure, and if it could reach Earth's atmosphere it would erode it. However, it is kept away by the pressure of the Earth's magnetic field. The magnetopause, the area where the pressures balance, is the boundary of the magnetosphere. Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 Earth radii out but the other side stretching out in a magnetotail that extends beyond 200 Earth radii. Sunward of the magnetopause is the bow shock, the area where the solar wind slows abruptly.

Inside the magnetosphere is the plasmasphere, a donut-shaped region containing low-energy charged particles, or plasma. This region begins at a height of 60 km, extends up to 3 or 4 Earth radii, and includes the ionosphere. This region rotates with the Earth. There are also two concentric tire-shaped regions, called the Van Allen radiation belts, with high-energy ions (energies from 0.1 to 10 million electron volts (MeV)). The inner belt is 1–2 Earth radii out while the outer belt is at 4–7 Earth radii. The plasmasphere and Van Allen belts have partial overlap, with the extent of overlap varying greatly with solar activity.

As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays, high-energy charged particles that are mostly from outside the Solar System. Many cosmic rays are kept out of the Solar System by the Sun's magnetosphere, or heliosphere. By contrast, astronauts on the Moon risk exposure to radiation. Anyone who had been on the Moon's surface during a particularly violent solar eruption in 2005 would have received a lethal dose.

Some of the charged particles do get into the magnetosphere. These spiral around field lines, bouncing back and forth between the poles several times per second. In addition, positive ions slowly drift westward and negative ions drift eastward, giving rise to a ring current. This current reduces the magnetic field at the Earth's surface. Particles that penetrate the ionosphere and collide with the atoms there give rise to the lights of the aurorae and also emit X-rays.

The varying conditions in the magnetosphere, known as space weather, are largely driven by solar activity. If the solar wind is weak, the magnetosphere expands; while if it is strong, it compresses the magnetosphere and more of it gets in. Periods of particularly intense activity, called geomagnetic storms, can occur when a coronal mass ejection erupts above the Sun and sends a shock wave through the Solar System. Such a wave can take just two days to reach the Earth. Geomagnetic storms can cause a lot of disruption; the "Halloween" storm of 2003 damaged more than a third of NASA's satellites. The largest documented storm occurred in 1859. It induced currents strong enough to short out telegraph lines, and aurorae were reported as far south as Hawaii.

Time dependence

Short-term variations

Background: a set of traces from magnetic observatories showing a magnetic storm in 2000.
Globe: map showing locations of observatories and contour lines giving horizontal magnetic intensity in μ T.

The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the ionosphere (ionospheric dynamo region) and magnetosphere, and some changes can be traced to geomagnetic storms or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich core.

Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the K-index.

Data from THEMIS show that the magnetic field, which interacts with the solar wind, is reduced when the magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in blackouts and disruptions in artificial satellites.

Secular variation

Estimated declination contours by year, 1590 to 1990 (click to see variation).

Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020.

Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation. Over hundreds of years, magnetic declination is observed to vary over tens of degrees. The animation shows how global declinations have changed over the last few centuries.

The direction and intensity of the dipole change over time. Over the last two centuries the dipole strength has been decreasing at a rate of about 6.3% per century. At this rate of decrease, the field would be negligible in about 1600 years. However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual.

A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2 degrees per year. This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD.

Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as paleomagnetic secular variation or paleosecular variation (PSV). The records typically include long periods of small change with occasional large changes reflecting geomagnetic excursions and reversals.

In July 2020 scientists report that analysis of simulations and a recent observational field model show that maximum rates of directional change of Earth's magnetic field reached ~10° per year – almost 100 times faster than current changes and 10 times faster than previously thought.

Studies of lava flows on Steens Mountain, Oregon, indicate that the magnetic field could have shifted at a rate of up to 6 degrees per day at some time in Earth's history, which significantly challenges the popular understanding of how the Earth's magnetic field works. This finding was later attributed to unusual rock magnetic properties of the lava flow under study, not rapid field change, by one of the original authors of the 1995 study.

Magnetic field reversals

Geomagnetic polarity during the late Cenozoic Era. Dark areas denote periods where the polarity matches today's polarity, light areas denote periods where that polarity is reversed.

Although generally Earth's field is approximately dipolar, with an axis that is nearly aligned with the rotational axis, occasionally the North and South geomagnetic poles trade places. Evidence for these geomagnetic reversals can be found in basalts, sediment cores taken from the ocean floors, and seafloor magnetic anomalies. Reversals occur nearly randomly in time, with intervals between reversals ranging from less than 0.1 million years to as much as 50 million years. The most recent geomagnetic reversal, called the Brunhes–Matuyama reversal, occurred about 780,000 years ago. A related phenomenon, a geomagnetic excursion, takes the dipole axis across the equator and then back to the original polarity. The Laschamp event is an example of an excursion, occurring during the last ice age (41,000 years ago).

The past magnetic field is recorded mostly by strongly magnetic minerals, particularly iron oxides such as magnetite, that can carry a permanent magnetic moment. This remanent magnetization, or remanence, can be acquired in more than one way. In lava flows, the direction of the field is "frozen" in small minerals as they cool, giving rise to a thermoremanent magnetization. In sediments, the orientation of magnetic particles acquires a slight bias towards the magnetic field as they are deposited on an ocean floor or lake bottom. This is called detrital remanent magnetization.

Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle, cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field. When the Earth's field reverses, new basalt records the reversed direction. The result is a series of stripes that are symmetric about the ridge. A ship towing a magnetometer on the surface of the ocean can detect these stripes and infer the age of the ocean floor below. This provides information on the rate at which seafloor has spread in the past.

Radiometric dating of lava flows has been used to establish a geomagnetic polarity time scale, part of which is shown in the image. This forms the basis of magnetostratigraphy, a geophysical correlation technique that can be used to date both sedimentary and volcanic sequences as well as the seafloor magnetic anomalies.

Earliest appearance

Paleomagnetic studies of Paleoarchean lava in Australia and conglomerate in South Africa have concluded that the magnetic field has been present since at least about 3,450 million years ago.

Future

Variations in virtual axial dipole moment since the last reversal.

At present, the overall geomagnetic field is becoming weaker; the present strong deterioration corresponds to a 10–15% decline over the last 150 years and has accelerated in the past several years; geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value achieved approximately 2,000 years ago. The rate of decrease and the current strength are within the normal range of variation, as shown by the record of past magnetic fields recorded in rocks.

The nature of Earth's magnetic field is one of heteroscedastic fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in the past for unknown reasons. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases.

The Earth's magnetic north pole is drifting from northern Canada towards Siberia with a presently accelerating rate—10 kilometres (6.2 mi) per year at the beginning of the 20th century, up to 40 kilometres (25 mi) per year in 2003, and since then has only accelerated.

Physical origin

Earth's core and the geodynamo

The Earth's magnetic field is believed to be generated by electric currents in the conductive iron alloys of its core, created by convection currents due to heat escaping from the core. However the process is complex, and computer models that reproduce some of its features have only been developed in the last few decades.

A schematic illustrating the relationship between motion of conducting fluid, organized into rolls by the Coriolis force, and the magnetic field the motion generates.

The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids. The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core. The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about 6,000 K (5,730 °C; 10,340 °F), to the core-mantle boundary, which is about 3,800 K (3,530 °C; 6,380 °F). The heat is generated by potential energy released by heavier materials sinking toward the core (planetary differentiation, the iron catastrophe) as well as decay of radioactive elements in the interior. The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.

The mechanism by which the Earth generates a magnetic field is known as a dynamo. The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force). These effects can be combined in a partial differential equation for the magnetic field called the magnetic induction equation,

{\displaystyle {\frac {\partial \mathbf {B} }{\partial t}}=\eta \nabla ^{2}\mathbf {B} +\nabla \times (\mathbf {u} \times \mathbf {B} ),}

where $u$ is the velocity of the fluid; $B$ is the magnetic B-field; and $η=1/σμ$ is the magnetic diffusivity, which is inversely proportional to the product of the electrical conductivity $σ$ and the permeability $μ$ . The term $\partial B /\partial t$ is the time derivative of the field; $\nabla 2$ is the Laplace operator and $\nabla\times$ is the curl operator.

The first term on the right hand side of the induction equation is a diffusion term. In a stationary fluid, the magnetic field declines and any concentrations of field spread out. If the Earth's dynamo shut off, the dipole part would disappear in a few tens of thousands of years.

In a perfect conductor ( $\sigma =\infty \;$ ), there would be no diffusion. By Lenz's law, any change in the magnetic field would be immediately opposed by currents, so the flux through a given volume of fluid could not change. As the fluid moved, the magnetic field would go with it. The theorem describing this effect is called the frozen-in-field theorem. Even in a fluid with a finite conductivity, new field is generated by stretching field lines as the fluid moves in ways that deform it. This process could go on generating new field indefinitely, were it not that as the magnetic field increases in strength, it resists fluid motion.

The motion of the fluid is sustained by convection, motion driven by buoyancy. The temperature increases towards the center of the Earth, and the higher temperature of the fluid lower down makes it buoyant. This buoyancy is enhanced by chemical separation: As the core cools, some of the molten iron solidifies and is plated to the inner core. In the process, lighter elements are left behind in the fluid, making it lighter. This is called compositional convection. A Coriolis effect, caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north–south polar axis.

A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which the solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for the geodynamo.

The average magnetic field in the Earth's outer core was calculated to be 25 gauss, 50 times stronger than the field at the surface.

Numerical models

Simulating the geodynamo by computer requires numerically solving a set of nonlinear partial differential equations for the magnetohydrodynamics (MHD) of the Earth's interior. Simulation of the MHD equations is performed on a 3D grid of points and the fineness of the grid, which in part determines the realism of the solutions, is limited mainly by computer power. For decades, theorists were confined to creating kinematic dynamo computer models in which the fluid motion is chosen in advance and the effect on the magnetic field calculated. Kinematic dynamo theory was mainly a matter of trying different flow geometries and testing whether such geometries could sustain a dynamo.

The first self-consistent dynamo models, ones that determine both the fluid motions and the magnetic field, were developed by two groups in 1995, one in Japan and one in the United States. The latter received attention because it successfully reproduced some of the characteristics of the Earth's field, including geomagnetic reversals.

Currents in the ionosphere and magnetosphere

Electric currents induced in the ionosphere generate magnetic fields (ionospheric dynamo region). Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations that can deflect surface magnetic fields by as much as one degree. Typical daily variations of field strength are about 25 nanoteslas (nT) (one part in 2000), with variations over a few seconds of typically around 1 nT (one part in 50,000).

Measurement and analysis

Detection

The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1832 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. The Magsat satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later Ørsted satellite allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of South Africa.

Governments sometimes operate units that specialize in measurement of the Earth's magnetic field. These are geomagnetic observatories, typically part of a national Geological survey, for example, the British Geological Survey's Eskdalemuir Observatory. Such observatories can measure and forecast magnetic conditions such as magnetic storms that sometimes affect communications, electric power, and other human activities.

The International Real-time Magnetic Observatory Network, with over 100 interlinked geomagnetic observatories around the world, has been recording the Earth's magnetic field since 1991.

The military determines local geomagnetic field characteristics, in order to detect anomalies in the natural background that might be caused by a significant metallic object such as a submerged submarine. Typically, these magnetic anomaly detectors are flown in aircraft like the UK's Nimrod or towed as an instrument or an array of instruments from surface ships.

Commercially, geophysical prospecting companies also use magnetic detectors to identify naturally occurring anomalies from ore bodies, such as the Kursk Magnetic Anomaly.

Crustal magnetic anomalies

A model of short-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies

Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and even ditches and middens in archaeological geophysics. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. Basalt — the iron-rich, volcanic rock making up the ocean floor — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.

Statistical models

Each measurement of the magnetic field is at a particular place and time. If an accurate estimate of the field at some other place and time is needed, the measurements must be converted to a model and the model used to make predictions.

Spherical harmonics

Schematic representation of spherical harmonics on a sphere and their nodal lines.

P ℓ m

is equal to 0 along

m

great circles passing through the poles, and along

ℓ- m

circles of equal latitude. The function changes sign each ℓtime it crosses one of these lines.

Example of a quadrupole field. This can also be constructed by moving two dipoles together.

The most common way of analyzing the global variations in the Earth's magnetic field is to fit the measurements to a set of spherical harmonics. This was first done by Carl Friedrich Gauss. Spherical harmonics are functions that oscillate over the surface of a sphere. They are the product of two functions, one that depends on latitude and one on longitude. The function of longitude is zero along zero or more great circles passing through the North and South Poles; the number of such nodal lines is the absolute value of the order $m$ . The function of latitude is zero along zero or more latitude circles; this plus the order is equal to the degree ℓ. Each harmonic is equivalent to a particular arrangement of magnetic charges at the center of the Earth. A monopole is an isolated magnetic charge, which has never been observed. A dipole is equivalent to two opposing charges brought close together and a quadrupole to two dipoles brought together. A quadrupole field is shown in the lower figure on the right.

Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties. A magnetic field is a vector field, but if it is expressed in Cartesian components $X, Y, Z$ , each component is the derivative of the same scalar function called the magnetic potential. Analyses of the Earth's magnetic field use a modified version of the usual spherical harmonics that differ by a multiplicative factor. A least-squares fit to the magnetic field measurements gives the Earth's field as the sum of spherical harmonics, each multiplied by the best-fitting Gauss coefficient $g m ℓ$ or $h m ℓ$ .

The lowest-degree Gauss coefficient, $g 00$ , gives the contribution of an isolated magnetic charge, so it is zero. The next three coefficients – $g 10$ , $g 11$ , and $h 11$ – determine the direction and magnitude of the dipole contribution. The best fitting dipole is tilted at an angle of about 10° with respect to the rotational axis, as described earlier.

Radial dependence

Spherical harmonic analysis can be used to distinguish internal from external sources if measurements are available at more than one height (for example, ground observatories and satellites). In that case, each term with coefficient $g m ℓ$ or $h m ℓ$ can be split into two terms: one that decreases with radius as $1/ r ℓ+1$ and one that increases with radius as $r ℓ$ . The increasing terms fit the external sources (currents in the ionosphere and magnetosphere). However, averaged over a few years the external contributions average to zero.

The remaining terms predict that the potential of a dipole source ( $ℓ=1$ ) drops off as $1/ r 2$ . The magnetic field, being a derivative of the potential, drops off as $1/ r 3$ . Quadrupole terms drop off as $1/ r 4$ , and higher order terms drop off increasingly rapidly with the radius. The radius of the outer core is about half of the radius of the Earth. If the field at the core-mantle boundary is fit to spherical harmonics, the dipole part is smaller by a factor of about 8 at the surface, the quadrupole part by a factor of 16, and so on. Thus, only the components with large wavelengths can be noticeable at the surface. From a variety of arguments, it is usually assumed that only terms up to degree $14$ or less have their origin in the core. These have wavelengths of about 2,000 kilometres (1,200 mi) or less. Smaller features are attributed to crustal anomalies.

Global models

The International Association of Geomagnetism and Aeronomy maintains a standard global field model called the International Geomagnetic Reference Field. It is updated every five years. The 11th-generation model, IGRF11, was developed using data from satellites (Ørsted, CHAMP and SAC-C) and a world network of geomagnetic observatories. The spherical harmonic expansion was truncated at degree 10, with 120 coefficients, until 2000. Subsequent models are truncated at degree 13 (195 coefficients).

Another global field model, called the World Magnetic Model, is produced jointly by the United States National Centers for Environmental Information (formerly the National Geophysical Data Center) and the British Geological Survey. This model truncates at degree 12 (168 coefficients) with an approximate spatial resolution of 3,000 kilometers. It is the model used by the United States Department of Defense, the Ministry of Defence (United Kingdom), the United States Federal Aviation Administration (FAA), the North Atlantic Treaty Organization (NATO), and the International Hydrographic Organization as well as in many civilian navigation systems.

A third model, produced by the Goddard Space Flight Center (NASA and GSFC) and the Danish Space Research Institute, uses a "comprehensive modeling" approach that attempts to reconcile data with greatly varying temporal and spatial resolution from ground and satellite sources.

For users with higher accuracy needs, the United States National Centers for Environmental Information developed the Enhanced Magnetic Model (EMM), which extends to degree and order 790 and resolves magnetic anomalies down to a wavelength of 56 kilometers. It was compiled from satellite, marine, aeromagnetic and ground magnetic surveys. As of 2018, the latest version, EMM2017, includes data from The European Space Agency's Swarm satellite mission.

Effect of ocean tides

The oceans contribute to Earth's magnetic field. Seawater is an electrical conductor, and therefore interacts with the magnetic field. As the tides cycle around the ocean basins, the ocean water essentially tries to pull the geomagnetic field lines along. Because the salty water is slightly conductive, the interaction is relatively weak: the strongest component is from the regular lunar tide that happens about twice per day. Other contributions come from ocean swell, eddies, and even tsunamis.

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Sea level magnetic fields observed by satellites (NASA)

The strength of the interaction depends also on the temperature of the ocean water. The entire heat stored in the ocean can now be inferred from observations of the Earth's magnetic field.

Biomagnetism

Animals, including birds and turtles, can detect the Earth's magnetic field, and use the field to navigate during migration. Some researchers have found that cows and wild deer tend to align their bodies north–south while relaxing, but not when the animals are under high-voltage power lines, suggesting that magnetism is responsible. Other researchers reported in 2011 that they could not replicate those findings using different Google Earth images.

Very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds, which use the Earth's magnetic field to navigate. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds; instead, the culprits have frequencies between 2 kHz and 5 MHz. These include AM radio signals and ordinary electronic equipment that might be found in businesses or private homes.

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