Frederik Pohl

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https://en.wikipedia.org/wiki/Frederik_Pohl

 

Frederik Pohl
Pohl in 2008 at the J. Lloyd Eaton Science Fiction Conference
Born	Frederik George Pohl Jr. November 26, 1919 New York City, United States
Died	September 2, 2013 (aged 93) Palatine, Illinois, United States
Pen name	Edson McCann, Jordan Park, Elton V. Andrews, Paul Fleur, Lee Gregor, Warren F. Howard, Scott Mariner, Ernst Mason, James McCreigh, Dirk Wilson, Donald Stacy
Occupation	Novelist, short story author, essayist, publisher, editor, literary agent
Nationality	American
Period	1939–2013
Genre	Science fiction
Notable awards	Campbell Memorial Award 1978, 1985 Hugo Award (novel) 1978 National Book Award 1980 Nebula Award (novel) 1976, 1977
Website
frederikpohl.com

Frederik George Pohl Jr. (/poʊl/; November 26, 1919 – September 2, 2013) was an American science-fiction writer, editor, and fan, with a career spanning more than 75 years—from his first published work, the 1937 poem "Elegy to a Dead Satellite: Luna", to the 2011 novel All the Lives He Led and articles and essays published in 2012.

From about 1959 until 1969, Pohl edited Galaxy and its sister magazine If; the latter won three successive annual Hugo Awards as the year's best professional magazine. His 1977 novel Gateway won four "year's best novel" awards: the Hugo voted by convention participants, the Locus voted by magazine subscribers, the Nebula voted by American science-fiction writers, and the juried academic John W. Campbell Memorial Award. He won the Campbell Memorial Award again for the 1984 collection of novellas Years of the City, one of two repeat winners during the first 40 years. For his 1979 novel Jem, Pohl won a U.S. National Book Award in the one-year category Science Fiction. It was a finalist for three other year's best novel awards. He won four Hugo and three Nebula Awards,^[2] including receiving both for the 1977 novel Gateway.

The Science Fiction Writers of America named Pohl its 12th recipient of the Damon Knight Memorial Grand Master Award in 1993 and he was inducted by the Science Fiction and Fantasy Hall of Fame in 1998, its third class of two dead and two living writers.

Pohl won the Hugo Award for Best Fan Writer in 2010, for his blog, "The Way the Future Blogs".

Early life and family

Pohl was the son of Frederik (originally Friedrich) George Pohl (a salesman of Germanic descent) and Anna Jane Mason. Pohl Sr. held various jobs, and the Pohls lived in such wide-flung locations as Texas, California, New Mexico, and the Panama Canal Zone. The family settled in Brooklyn when Pohl was around seven.

He attended Brooklyn Technical High School, and dropped out at 17. In 2009, he was awarded an honorary diploma from Brooklyn Tech.

While a teenager, he co-founded the New York–based Futurians fan group, and began lifelong friendships with Donald Wollheim, Isaac Asimov, and others who would become important writers and editors. Pohl later said that other "friends came and went and were gone, [but] many of the ones I met through fandom were friends all their lives – Isaac, Damon Knight, Cyril Kornbluth, Dirk Wylie, [and] Dick Wilson. In fact, there are one or two – Jack Robins, Dave Kyle – whom I still count as friends, seventy-odd years later...." He published a science-fiction fanzine called Mind of Man. 

During 1936, Pohl joined the Young Communist League because of its positions for unions and against racial prejudice, Adolf Hitler, and Benito Mussolini. He became president of the local Flatbush III Branch of the YCL in Brooklyn. Pohl has said that after the Molotov–Ribbentrop Pact of 1939, the party line changed and he could no longer support it, at which point he left.

Pohl served in the United States Army from April 1943 until November 1945, rising to sergeant as an air corps weatherman. After training in Illinois, Oklahoma, and Colorado, he was mainly stationed in Italy with the 456th Bombardment Group.

Pohl was married five times. His first wife, Leslie Perri, was another Futurian; they were married in August 1940, and divorced in 1944. He then married Dorothy LesTina in Paris in August 1945 while both were serving in the military in Europe; the marriage ended in 1947. During 1948, he married Judith Merril; they had a daughter, Ann. Pohl and Merril divorced in 1952. In 1953, he married Carol M. Ulf Stanton, with whom he had three children and collaborated on several books; they separated in 1977 and were divorced in 1983. From 1984 until his death, Pohl was married to science-fiction expert and academic Elizabeth Anne Hull.

He fathered four children – Ann (m. Walter Weary), Frederik III (deceased), Frederik IV and Kathy. Grandchildren include Canadian writer Emily Pohl-Weary and chef Tobias Pohl-Weary.

From 1984 on, he lived in Palatine, Illinois, a suburb of Chicago. He was previously a longtime resident of Middletown, New Jersey.

Career

Frederik Pohl (center) with fellow scifi authors Donald A. Wollheim and John Michel in 1938

Early career

Pohl began writing in the late 1930s, using pseudonyms for most of his early works. His first publication was the poem "Elegy to a Dead Satellite: Luna" under the name of Elton Andrews, in the October 1937 issue of Amazing Stories, edited by T. O'Conor Sloane. (Pohl asked readers 30 years later, "we would take it as a personal favor if no one ever looked it up".) His first story, the collaboration with C.M. Kornbluth "Before the Universe", appeared in 1940 under the pseudonym S.D. Gottesman.

Work as editor and agent

Pohl started a career as a literary agent in 1937, but it was a sideline for him until after World War II, when he began doing it full-time. He ended up "representing more than half the successful writers in science fiction", but his agency did not succeed financially, and he closed it down in the early 1950s. 

Pohl stopped being Asimov's agent—the only one the latter ever had—when he became editor from 1939 to 1943 of two pulp magazines, Astonishing Stories and Super Science Stories. Stories by Pohl often appeared in these science-fiction magazines, but never under his own name. Work written in collaboration with Cyril M. Kornbluth was credited to S. D. Gottesman or Scott Mariner; other collaborative work (with any combination of Kornbluth, Dirk Wylie, or Robert A. W. Lownes) was credited to Paul Dennis Lavond. For Pohl's solo work, stories were credited to James MacCreigh (or for one story only, Warren F. Howard.) Works by "Gottesman", "Lavond", and "MacCreigh" continued to appear in various science-fiction pulp magazines throughout the 1940s. 

In his autobiography, Pohl said that he stopped editing the two magazines at roughly the time of the German invasion of the Soviet Union in 1941. 

Pohl co-founded the Hydra Club, a loose collection of science-fiction professionals and fans who met during the late 1940s and 1950s.

From the early 1960s until 1969, Pohl served as editor of Galaxy Science Fiction and Worlds of if magazines, taking over after the ailing H. L. Gold could no longer continue working "around the end of 1960". Under his leadership, if won the Hugo Award for Best Professional Magazine for 1966, 1967 and 1968. Pohl hired Judy-Lynn del Rey as his assistant editor at Galaxy and if. He also served as editor of Worlds of Tomorrow from its first issue in 1963 until it was merged into if in 1967.

In the mid-1970s, Pohl acquired and edited novels for Bantam Books, published as "Frederik Pohl Selections"; these included Samuel R. Delany's Dhalgren and Joanna Russ's The Female Man. He also edited a number of science-fiction anthologies. 

Later career

After World War II, Pohl worked as an advertising copywriter and then as a copywriter and book editor for Popular Science. Following the war, Pohl began publishing material under his own name, much in collaboration with his fellow Futurian, Cyril Kornbluth.

Though the pen names of "Gottesman", "Lavond", and "MacCreigh" were retired by the early 1950s, Pohl still occasionally used pseudonyms, even after he began to publish work under his real name. These occasional pseudonyms, all of which date from the early 1950s to the early 1960s, included Charles Satterfield, Paul Flehr, Ernst Mason, Jordan Park (two collaborative novels with Kornbluth), and Edson McCann (one collaborative novel with Lester del Rey). 

In the 1970s, Pohl re-emerged as a novel writer in his own right, with books such as Man Plus and the Heechee series. He won back-to-back Nebula Awards with Man Plus in 1976 and Gateway, the first Heechee novel, in 1977. In 1978, Gateway swept the other two major novel honors, also winning the Hugo Award for Best Novel and John W. Campbell Memorial Award for the best science-fiction novel. Two of his stories have also earned him Hugo Awards: "The Meeting" (with Kornbluth) tied in 1973 and "Fermi and Frost" won in 1986. Another award-winning novel is Jem (1980), winner of the National Book Award. 

His works include not only science fiction, but also articles for Playboy and Family Circle magazines and nonfiction books. For a time, he was the official authority for Encyclopædia Britannica on the subject of Emperor Tiberius. (He wrote a book on the subject of Tiberius, as "Ernst Mason".)

Some of his short stories take a satirical look at consumerism and advertising in the 1950s and 1960s: "The Wizards of Pung's Corners", where flashy, over-complex military hardware proved useless against farmers with shotguns, and "The Tunnel under the World", where an entire community of seeming-humans is held captive by advertising researchers. ("The Wizards of Pung's Corners" was freely translated into Chinese and then freely translated back into English as "The Wizard-Masters of Peng-Shi Angle" in the first edition of Pohlstars (1984)). 

Pohl's Law is either "No one is ever ready for anything" or "Nothing is so good that somebody, somewhere will not hate it".

He was a frequent guest on Long John Nebel's radio show from the 1950s to the early 1970s, and an international lecturer.

Starting in 1995, when the Theodore Sturgeon Memorial Award became a juried award, Pohl served first with James Gunn and Judith Merril, and since then with several others until retiring in 2013. Pohl was associated with Gunn since the 1940s, becoming involved in 1975 with what later became Gunn's Center for the Study of Science Fiction at the University of Kansas. There, he presented many talks, recorded a discussion about "The Ideas in Science Fiction" in 1973 for the Literature of Science Fiction Lecture Series, and served the Intensive Institute on Science Fiction and Science Fiction Writing Workshop.

Pohl received the second annual J. W. Eaton Lifetime Achievement Award in Science Fiction from the University of California, Riverside Libraries at the 2009 Eaton Science Fiction Conference, "Extraordinary Voyages: Jules Verne and Beyond".

Pohl's work has been an influence on a wide variety of other science fiction writers, some of whom appear in the 2010 anthology, Gateways: Original New Stories Inspired by Frederik Pohl, edited by Elizabeth Anne Hull.

Pohl's last novel, All the Lives He Led, was released on April 12, 2011.

By the time of his death, he was working to finish a second volume of his autobiography The Way the Future Was (1979), along with an expanded version of the latter.

Collaborative work

In addition to his solo writings, Pohl was also well known for his collaborations, beginning with his first published story. Before and following the war, Pohl did a series of collaborations with his friend Cyril Kornbluth, including a large number of short stories and several novels, among them The Space Merchants, a dystopian satire of a world ruled by the advertising agencies.

In the mid-1950s, he began a long-running collaboration with Jack Williamson, eventually resulting in 10 collaborative novels over five decades.

Other collaborations included a novel with Lester Del Rey, Preferred Risk (1955). This novel was solicited for a contest by Galaxy–Simon & Schuster when the judges did not think any of the contest submissions was good enough to win their contest. It was published under the joint pseudonym Edson McCann. He also collaborated with Thomas T. Thomas on a sequel to his award-winning novel Man Plus. He wrote two short stories with Isaac Asimov in the 1940s, both published in 1950.

He finished a novel begun by Arthur C. Clarke, The Last Theorem, which was published on August 5, 2008. 

Death

Pohl went to the hospital in respiratory distress on the morning of September 2, 2013, and died that afternoon at the age of 93.

Works

Main article: List of works by Frederik Pohl

Uplift Universe

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Uplift_Universe

The Uplift Universe is a fictional universe created by American science fiction writer David Brin. A central feature in this universe is the process of biological uplift.

His books which take place in this universe are:

• Sundiver (1980)
• Startide Rising (1983)
• The Uplift War (1987)
• The Uplift Trilogy (sometimes called the Uplift Storm trilogy):
  • Brightness Reef (1995)
  • Infinity's Shore (1996)
  • Heaven's Reach (1998)

There is also a short story, "Aficionado" (originally titled "Life in the Extreme"), published in 1998, which serves as a prequel to the series as a whole (it also serves as a part of Existence, an unrelated work by Brin), and a novella, Temptation, published in 1999 in Far Horizons, which follows on from Heaven's Reach. He also wrote Contacting Aliens: An Illustrated Guide to David Brin's Uplift Universe, a guidebook about the background of the series.

At least one more Uplift book is planned by Brin, as he has stated in 2012 that Temptation "will be a core element of the next Uplift novel... and answers several unresolved riddles left over from Heaven's Reach."

GURPS Uplift is a sourcebook for a science fiction themed role-playing game based on the Uplift Universe. It includes a few stories that happen in Jijo after the end of Heaven's Reach.

Setting

In the Uplift universe an intergalactic civilization called the Five Galaxies, comprising a multitude of sapient races, has existed for billions of years. This civilization is perpetuated by the act of "uplift", in which a "patron" species genetically modifies a pre-sapient "client" species until it is sapient. The client species is typically indentured to its patron species for 100,000 years. A patron species gains considerable status, and patrons and clients often unite into powerful clans. Patron status can be lost due to extermination, or gross crimes against the galactic civilization. 

It is generally accepted in this universe that the process of uplift was initiated at least one billion years ago by a species known only as the Progenitors. Humanity is therefore an anomaly – a species with no apparent patron race. Whether humanity truly evolved independently, or whether it was criminally abandoned by an unknown patron early in its uplift, is a topic of fierce debate. Most of humanity believes itself to be a "wolfling" species that emerged into sapience solely through natural evolution, without genetic manipulation by a patron species. This belief is considered heresy and ridiculous by most of the galactic civilization and has made most of the galactic powers enemies of EarthClan. The fact that humanity had already uplifted two species (chimpanzees and bottlenose dolphins) when it encountered the galactic civilization gave humanity patron status, which is one of the few lucky turns it has had in its difficult position as pariah in the galactic civilization. This saved humanity from the likely fate of becoming client to another race through forced adoption or being punitively exterminated for the environmental damage done to the Earth and its native species. 

Humanity and its clients are collectively known as EarthClan. Humanity in the Uplift universe is not a dominant nor a technologically advanced species – it is centuries, even millennia, behind the great galactic powers and has several enemies capable of exterminating it entirely.

The civilization of the Five Galaxies has several "Institutes", which are bureaucracies that specify how species deal with each other and the uplift process. One of the most significant of these is the Library Institute, the repository of all knowledge. Humanity prides itself on using the Library as little as possible. For instance, instead of drawing upon the highly refined starship designs available in the Library, humanity tends to develop its own (generally vastly inferior) vessels. Humans feel that this is a way to exercise their own independence and creativity, and it occasionally allows them to find solutions to problems which have in fact surprised more powerful races.

The Institute of Migration determines what planets can be colonized and under what environmental restrictions, primarily to ensure that suitable races can still evolve for later uplift. The Institute also ensures the separation of the hydrogen-breathing and oxygen-breathing orders of sapient life. Other intergalactic institutes regulate the uplift of sapient species, navigation, warfare, etc. Bureaucrats are recruited from all races but are expected to put the interests of their bureau before that of their race and maintain strict neutrality; however, this does not always happen.

The civilization of the Five Galaxies is made up solely of oxygen-breathing species. This civilization is aware of, but by tradition rarely if ever interacts with, the other orders of sapient life, which include those which are hydrogen-breathing, transcendent, mechanical, memetic, and quantum. There is also a special designation for hypothetical orders of life which could also exist but have not been discovered. 

Technology

Unlike most other races, humans and their clients regard creativity as very desirable – the others take the view that everything useful has already been discovered, so it would be more efficient to search the Galactic Library for whatever they need. EarthClan are also considered odd for using archaic technology in addition to the more advanced Galactic technology, or sometimes preferring primitive technologies that they understand to more advanced ones that they don't yet understand. Most notably, EarthClan utilizes calculus, which is unknown and mistrusted by galactic society. All other races simply apply brute-force, finite-element analysis to any problem due to their ability to apply as much computing power as may be needed to model all phenomena.

Social behavior

Most Galactic "clans" are rather feudal and sometimes exploitative, and place strong emphasis on etiquette and especially on deferential behavior by members of "subordinate" races towards members of "superior" races. Hence they often regard EarthClan's informal speech as insulting and the humans' egalitarian treatment of their Neo-Chimp and Neo-Dolphin clients as foolish, if not outright offensive.

Languages

Most of EarthClan speaks Anglic. Galactics have several specialized languages:

• Gal One: Purely mathematical and similar to Morse code. Extremely slow.
• Gal Two: Bridging language.
• Gal Three: Squeaks and honks. Favored by the Gubru.
• Gal Four: Sonar based.
• Gal Five: Grunts and growls. Used by the T'4Lek.
• Gal Six: Hisses. Synthians and Thennanins.
• Gal Seven: Tone language. Tymbrimi.
• Gal Eight: Hoots and honks. Jophur and Rosh.
• Gal Nine: Chiming, syncopated. Kanten, Linten, Siqul.
• Gal Ten: Fluting, sonar-like. Brothers of the Night.
• Gal Eleven: Bridging language. Cautious, often redundant. Used between different Orders of life.
• Gal Twelve: Throaty, used by the Soro. 2 billion years old.
  

Planets

The following planets feature in the books, from the many thousands of inhabited planets in the setting:

• Calafia: A water-world inhabited by humans and Neo-Dolphins, currently occupied by the Soro. The name may refer to Calafia, a mythical Black Amazon.
• Cathrhennlin: A Tymbrimi university world.
• Deemi: A world leased to humans on the condition that they run the Galactic prison located there. It is bathed in ultraviolet radiation. Most of its biosphere is aquatic.
• Garth: The main setting of the novel The Uplift War, which depicts its invasion by the Gubru. The planet was leased to EarthClan after its ecology was devastated by the Bururalli species, and is inhabited by humans and Neo-Chimpanzees. Its star is called Gimelhai, and its main city is Port Helenia.
• Horst: A disaster world, assigned to Humanity less than six generations before the Streaker crisis, and populated by primitivists.
• Jijo: The main setting of the novels Brightness Reef, Infinity's Shore, and Heaven's Reach. It is a planet orbiting a carbon star in Galaxy 4, illegally inhabited by refugees from ten species: humans, chimpanzees, dolphins, Hoon, G'Kek, Urs, Traeki, Glavers, Qheuen, and Tytlal. It is also used as a refuge by the EarthClan starship Streaker. Brin uses the mix of species to explore commonalities of the sapient experience; for example Hoon Alvin Hph-Wayuo is a humicker, an enthusiast and imitator of human culture.^[6]
• Jophekka: The homeworld of the Jophur, sapient and ambitious sap ring stacks.
• Juthtath: A Tymbrimi world.
• Kazzkark: Minor planet, where an important base of the Navigation Institute gathers data from E-Space.
• Kithrup: The main setting of the novel Startide Rising, where the EarthClan starship Streaker takes refuge from its many pursuers. It is a metal-rich, watery world orbiting the star Kthsemenee. It is inhabited by the pre-sapient Kiqui, and serves as the recuperation home for the psionic Karrank%.
• NuDawn: A pre-Contact colony (whose name may be a pun with Aurora - New Dawn) where an incident with Hoon inspectors brought Jophur to massacre the human colonists.
• Oakka: A "green-green" world, where the air is difficult to breathe. There was a Library branch there, but its inhabitants were corrupted and attacked the Streaker in an attempt to capture it.
• Omnivarium: A world inhabited by birds that mimic any sound, a fact discovered when the birds started mimicking the sounds of explorers performing coitus.
• Tanith: The location of the nearest full Galactic Library branch near Terra.
• Urchachka: A very dry planet, homeworld of the Urs.
  

Alien species and humans

EarthClan

EarthClan is the name of humanity and their clients (an animal or plant species being uplifted) in David Brin's Uplift Universe. They are named for their combined homeworld Earth. 

In the books, humanity is an insignificant race, having no known Patrons (a species responsible for uplifting them) and having mostly primitive technology. Humans have two (confirmed) clients and are referred to formally as "a-Human ul-Chimpanzee ul-Dolphin". However, in being Patrons, humanity has unknowingly protected itself from being forced into becoming a client of an older race. 

Humans

Humans in the Uplift universe are surprisingly baseline. Advanced augmentative technologies exist, but appear to be too expensive or socially frowned upon to be in widespread use. So, while cybernetics, advanced genetic engineering, and other technology capable of creating trans-humans exists, they are not in widespread use, as very few characters are portrayed using such technologies.

Neo-Chimpanzees

Chimpanzees are the first clients of humans and are the most "complete" in that they are closest to full sapiency. They are Stage 2 clients but almost became Stage 3 when the Gubru invaded Garth. Neo-Chimpanzees like music, specifically percussion. They are embarrassed by situations which remind them of their earlier status as "smart animals", especially about nudity, tree-climbing and above all losing their ability to speak when under stress.

Neo-Dolphins

Dolphins are the second clients of humans, and are some of the best pilots in the Five Galaxies because their aquatic origins give them excellent instincts for 3-D maneuvers. They are also important in planetary warfare because most Galactics are unaware of the strategic potential of the sea. Neo-Dolphins are Stage-2 Clients, and recently got their own starship, Streaker (Streaker's discoveries later caused controversy among the oxygen-breathing sapient species). Neo-Dolphins are at a relatively early stage of uplift, and this has several consequences which are important in the plots of the stories: the optimal genetic mix for Neo-Dolphins has not yet been determined, and some of the newer genetic mixes become dangerous to colleagues when under stress; there are significant differences between older and younger Neo-Dolphins, in particular older individuals find it more difficult to speak; and they have to struggle against tendencies to slip into atavistic behaviours such as the "Whale Dream" and rescue fever (which leads them to beach themselves).

Neo-Gorillas

Neo-Gorillas were at a very early stage of uplift when the Galactic Uplift Institute ordered humans to halt the process, because they were concerned that humans could not manage so many uplift projects at the same time. Some humans secretly continued the project on the small colony-world of Garth. Neo-Gorillas have some understanding that they are being uplifted, and chose the Thennanin as their "patrons" at a ceremony on Garth. This is politically very important, as the conservative and conscientious Thennanin are a major military power and the Neo-Gorillas' choice converts the Thennanin from enemies to allies of EarthClan. After adoption by the Thennanin, the Neo-Gorillas are termed "Garthlings."

Neo-Dogs

Dogs have been mentioned as a possible client of humanity in several books, but their final adoption has not been confirmed. 

Other clans (of aliens)

The Jophur

The Jophur are a fictional extraterrestrial race in the Uplift Universe. Physically, they are a stack of waxy, living rings. Each ring serves a different purpose, and they connect to each other to form a single being by chemical means via an electrically conductive, sap-like substance that flows down the center to bind the stack together. A "master ring" provides a strong sense of individuality to each stack and enforces this with corrective electrical shocks to non-compliant rings.

The Jophur were originally the traeki, intelligent but often indecisive because of internal debates between the rings that formed each individual. Their patrons, the Poa, asked the Oallie to engineer the traeki further to increase their effectiveness. The Oailie created "master rings", shiny black rings (often described as "silvery") that created a strong sense of self-identity. The newly invigorated Jophur, as the traeki with the new master rings were called, quickly became a strong, vigorous force in the Five Galaxies.

According to various books in the series, most prominently the trilogy that followed the characters of Startide Rising, the Jophur quickly began a genocide and eradicated all but a small group of the original traeki, with the exception of a small "Sooner" group that settled on the planet Jijo in the fourth galaxy. "Sooner" is a term from United States history, and is used in the Uplift stories to describe illegal settlers on worlds that have been declared fallow, i.e. to be left uncolonized so that native intelligences may have a chance to develop naturally. The Jophur became fanatical adherents of one of the galaxy's religious ideologies, and exterminated many races they regarded as "heretics" – including the g'Kek, which also survived only as a "Sooner" group on Jijo.

Kiqui

Kiqui are a pre-sapient amphibious species first discovered on the planet Kithrup by Streaker's crew, who persuade them to be uplifted as clients of the humans. If this goes ahead, the Kiqui would become humanity's first extraterrestrial clients.

Plot outline and major themes

Ecology and stewardship of genetic diversity are major themes in the Uplift books. Religious orthodoxy and the behavior of static societies are also themes.

The first book in the Uplift series, Sundiver (1980), is essentially a detective story and occurs only decades after humanity's first contact with the Five Galaxies. In this story mankind discovers the sun's inhabitants and a plot to overthrow a patron race. This is the only novel to directly involve Earth. 

The second book, Startide Rising (1983), occurs centuries later. It follows the Earthclan amphibious spaceship Streaker (crewed by uplifted dolphins and their human patrons) which has discovered a colossal derelict fleet. Streaker is pursued as rumors spread throughout the Five Galaxies that the ship has found the remains of the Progenitors. 

The third book, The Uplift War (1987), occurs around the same time as Startide Rising but in another part of the galaxy. An intergalactic war, sparked by the events of Startide Rising, results in a successful invasion of the EarthClan colony on the planet Garth, heavily populated by uplifted chimps. 

In 1995 Brightness Reef was published, the first book in a new Uplift trilogy. The "Uplift Storm" trilogy (excluding the first book, which solely focuses on Jijo) follows the survivors of the spaceship Streaker as they continue to evade the various galactic powers. Along the way they encounter a hidden planet which has been inhabited by six races which have illegally settled and dropped out of the civilization of the Five Galaxies. They eventually make contact with the other orders of life. The second and third books in the new Uplift trilogy are Infinity's Shore and Heaven's Reach.

In Heaven's Reach, the series sums up with conclusions on the nature of life in the universe and revelations on the motivations of the oldest species in the Five Galaxies. Further explanations are provided on the Streaker's continuing mission, Earth's fate after invasion, and the nature of galactic life in the overlapping conspiracies of galactic civilization. 

The short story "Aficionado" or "Life in the Extreme" is set earliest of all the currently written work and gives an account of the early days of the human uplift program before Contact. The contents of this story have since been reused as part of the unrelated novel Existence, making its position in the uplift universe uncertain.

The novella Temptation was set just after the ending of Heaven's Reach, and tells what happened to some of the characters from the trilogy after the main story ended.

Timeline

Below is a summarized timeline for events detailed in the Uplift Universe, which corresponds to the Gregorian Calendar:

Date	Event
2212	Contact with Galactic civilization
2246	Sundiver incident
2489	Events of Startide Rising
2492	Post Uplift War

Oort constants

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Oort_constants

The Oort constants (discovered by Jan Oort) ${\displaystyle A}$ and ${\displaystyle B}$ are empirically derived parameters that characterize the local rotational properties of our galaxy, the Milky Way, in the following manner:

${\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}-{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}\right)\\&B=-{\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}+{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}\right)\\\end{aligned}}}$

where ${\displaystyle V_{0}}$ and ${\displaystyle R_{0}}$ are the rotational velocity and distance to the Galactic center, respectively, measured at the position of the Sun, and v and r are the velocities and distances at other positions in our part of the galaxy. As derived below, A and B depend only on the motions and positions of stars in the solar neighborhood. As of 2018, the most accurate values of these constants are ${\displaystyle A}$ = 15.3 ± 0.4 km s⁻¹ kpc⁻¹, ${\displaystyle B}$ = -11.9 ± 0.4 km s⁻¹ kpc⁻¹. From the Oort constants, it is possible to determine the orbital properties of the Sun, such as the orbital velocity and period, and infer local properties of the Galactic disk, such as the mass density and how the rotational velocity changes as a function of radius from the Galactic center.

Historical significance and background

By the 1920s, a large fraction of the astronomical community had recognized that some of the diffuse, cloud-like objects, or nebulae, seen in the night sky were collections of stars located beyond our own, local collection of star clusters. These galaxies had diverse morphologies, ranging from ellipsoids to disks. The concentrated band of starlight that is the visible signature of the Milky Way was indicative of a disk structure for our galaxy; however, our location within our galaxy made structural determinations from observations difficult.

Classical mechanics predicted that a collection of stars could be supported against gravitational collapse by either random velocities of the stars or their rotation about its center of mass. For a disk-shaped collection, the support should be mainly rotational. Depending on the mass density, or distribution of the mass in the disk, the rotation velocity may be different at each radius from the center of the disk to the outer edge. A plot of these rotational velocities against the radii at which they are measured is called a rotation curve. For external disk galaxies, one can measure the rotation curve by observing the Doppler shifts of spectral features measured along different galactic radii, since one side of the galaxy will be moving towards our line of sight and one side away. However, our position in the Galactic midplane of the Milky Way, where dust in molecular clouds obscures most optical light in many directions, made obtaining our own rotation curve technically difficult until the discovery of the 21 cm hydrogen line in the 1930s.

To confirm the rotation of our galaxy prior to this, in 1927 Jan Oort derived a way to measure the Galactic rotation from just a small fraction of stars in the local neighborhood. As described below, the values he found for ${\displaystyle A}$ and ${\displaystyle B}$ proved not only that the Galaxy was rotating but also that it rotates differentially, or as a fluid rather than a solid body. 

Derivation

Figure 1: Geometry of the Oort constants derivation, with a field star close to the Sun in the midplane of the Galaxy.

 

Consider a star in the midplane of the Galactic disk with Galactic longitude ${\displaystyle l}$ at a distance ${\displaystyle d}$ from the Sun. Assume that both the star and the Sun have circular orbits around the center of the Galaxy at radii of ${\displaystyle R}$ and ${\displaystyle R_{0}}$ from the galactic center and rotational velocities of ${\displaystyle V}$ and ${\displaystyle V_{0}}$, respectively. The motion of the star along our line of sight, or radial velocity, and motion of the star across the plane of the sky, or transverse velocity, as observed from the position of the Sun are then:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=V_{\text{star, r}}-V_{\text{sun, r}}=V\cos \left(\alpha \right)-V_{0}\sin \left(l\right)\\&V_{\text{obs, t}}=V_{\text{star, t}}-V_{\text{sun, t}}=V\sin \left(\alpha \right)-V_{0}\cos \left(l\right)\\\end{aligned}}}$

With the assumption of circular motion, the rotational velocity is related to the angular velocity by ${\displaystyle v=\Omega r}$ and we can substitute this into the velocity expressions:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=\Omega R\cos \left(\alpha \right)-\Omega _{0}R_{0}\sin \left(l\right)\\&V_{\text{obs, t}}=\Omega R\sin \left(\alpha \right)-\Omega _{0}R_{0}\cos \left(l\right)\\\end{aligned}}}$

From the geometry in Figure 1, one can see that the triangles formed between the galactic center, the Sun, and the star share a side or portions of sides, so the following relationships hold and substitutions can be made:

${\displaystyle {\begin{aligned}&R\cos \left(\alpha \right)=R_{0}\sin \left(l\right)\\&R\sin \left(\alpha \right)=R_{0}\cos \left(l\right)-d\\\end{aligned}}}$

and with these we get

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=\left(\Omega -\Omega _{0}\right)R_{0}\sin \left(l\right)\\&V_{\text{obs, t}}=\left(\Omega -\Omega _{0}\right)R_{0}\cos \left(l\right)-\Omega d\\\end{aligned}}}$

To put these expressions only in terms of the known quantities ${\displaystyle l}$ and ${\displaystyle d}$, we take a Taylor expansion of ${\displaystyle \Omega -\Omega _{0}}$ about ${\displaystyle R_{0}}$.

${\displaystyle \left(\Omega -\Omega _{0}\right)=\left(R-R_{0}\right){\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}+...}$

Additionally, we take advantage of the assumption that the stars used for this analysis are local, i.e. ${\displaystyle R-R_{0}}$ is small, and the distance d to the star is smaller than ${\displaystyle R}$ or ${\displaystyle R_{0}}$, and we take:

${\displaystyle R-R_{0}=-d\cdot \cos \left(l\right)}$.

So:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=-R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}d\cdot \cos \left(l\right)\sin \left(l\right)\\&V_{\text{obs, t}}=-R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}d\cdot \cos ^{2}\left(l\right)-\Omega d\\\end{aligned}}}$

Using the sine and cosine half angle formulae, these velocities may be rewritten as:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=-R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}d{\frac {\sin \left(2l\right)}{2}}\\&V_{\text{obs, t}}=-R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}d{\frac {\left(\cos \left(2l\right)+1\right)}{2}}-\Omega d=-R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}d{\frac {\cos \left(2l\right)}{2}}+\left(-{\frac {1}{2}}R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}-\Omega \right)d\\\end{aligned}}}$

Writing the velocities in terms of our known quantities and two coefficients ${\displaystyle A}$ and ${\displaystyle B}$ yields:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=Ad\sin \left(2l\right)\\&V_{\text{obs, t}}=Ad\cos \left(2l\right)+Bd\\\end{aligned}}}$

where

${\displaystyle {\begin{aligned}&A=-{\frac {1}{2}}R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}\\&B=-{\frac {1}{2}}R_{0}{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}-\Omega \\\end{aligned}}}$

At this stage, the observable velocities are related to these coefficients and the position of the star. It is now possible to relate these coefficients to the rotation properties of the galaxy. For a star in a circular orbit, we can express the derivative of the angular velocity with respect to radius in terms of the rotation velocity and radius and evaluate this at the location of the Sun:

${\displaystyle {\begin{aligned}&\Omega ={\frac {v}{r}}\\&{\frac {d\Omega }{dr}}{\Bigg \vert }_{R_{0}}={\frac {d(v/r)}{dr}}{\Bigg \vert }_{R_{0}}=-{\frac {V_{0}}{R_{0}^{2}}}+{\frac {1}{R_{0}}}{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}\\\end{aligned}}}$

so

Oort constants on a wall in Leiden

${\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}-{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}\right)\\&B=-{\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}+{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}\right)\\\end{aligned}}}$

${\displaystyle A}$ is the Oort constant describing the shearing motion and ${\displaystyle B}$ is the Oort constant describing the rotation of the Galaxy. As described below, one can measure ${\displaystyle A}$ and ${\displaystyle B}$ from plotting these velocities, measured for many stars, against the galactic longitudes of these stars. 

Measurements

Figure 2: Measuring the Oort constants by fitting to large data sets. Note that this graph erroneously shows B as positive. A negative B value contributes a westerly component to the transverse velocities.

 

As mentioned in an intermediate step in the derivation above:

${\displaystyle {\begin{aligned}&V_{\text{obs, r}}=A\,d\,\sin \left(2l\right)\\&V_{\text{obs, t}}=A\,d\,\cos \left(2l\right)+B\,d\\\end{aligned}}}$

Therefore, we can write the Oort constants ${\displaystyle A}$ and ${\displaystyle B}$ as:

${\displaystyle {\begin{aligned}&A={\frac {V_{\text{obs, r}}}{d\,\sin \left(2l\right)}}\\&B={\frac {V_{\text{obs, t}}}{d}}-A\,\cos \left(2l\right)\\\end{aligned}}}$

Thus, the Oort constants can be expressed in terms of the radial and transverse velocities, distances, and galactic longitudes of objects in our Galaxy - all of which are, in principle, observable quantities.

However, there are a number of complications. The simple derivation above assumed that both the Sun and the object in question are traveling on circular orbits about the Galactic center. This is not true for the Sun (the Sun's velocity relative to the local standard of rest is approximately 13.4 km/s), and not necessarily true for other objects in the Milky Way either. The derivation also implicitly assumes that the gravitational potential of the Milky Way is axisymmetric and always directed towards the center. This ignores the effects of spiral arms and the Galaxy's bar. Finally, both transverse velocity and distance are notoriously difficult to measure for objects which are not relatively nearby. 

Since the non-circular component of the Sun's velocity is known, it can be subtracted out from our observations to compensate. We do not know, however, the non-circular components of the velocity of each individual star we observe, so they cannot be compensated for in this way. But, if we plot transverse velocity divided by distance against galactic longitude for a large sample of stars, we know from the equations above that they will follow a sine function. The non-circular velocities will introduce scatter around this line, but with a large enough sample the true function can be fit for and the values of the Oort constants measured, as shown in figure 2. ${\displaystyle A}$ is simply the amplitude of the sinusoid and ${\displaystyle B}$ is the vertical offset from zero. Measuring transverse velocities and distances accurately and without biases remains challenging, though, and sets of derived values for ${\displaystyle A}$ and ${\displaystyle B}$ frequently disagree. 

Most methods of measuring ${\displaystyle A}$ and ${\displaystyle B}$ are fundamentally similar, following the above patterns. The major differences usually lie in what sorts of objects are used and details of how distance or proper motion are measured. Oort, in his original 1927 paper deriving the constants, obtained ${\displaystyle A}$ = 31.0 ± 3.7 km s⁻¹ kpc⁻¹. He did not explicitly obtain a value for ${\displaystyle B}$, but from his conclusion that the Galaxy was nearly in Keplerian rotation (as in example 2 below), we can presume he would have gotten a value of around -10 km s⁻¹ kpc⁻¹. These differ significantly from modern values, which is indicative of the difficulty of measuring these constants. Measurements of ${\displaystyle A}$ and ${\displaystyle B}$ since that time have varied widely; in 1964 the IAU adopted ${\displaystyle A}$ = 15 km s⁻¹ kpc⁻¹ and ${\displaystyle B}$ = -10 km s⁻¹ kpc⁻¹ as standard values. Although more recent measurements continue to vary, they tend to lie near these values.

The Hipparcos satellite, launched in 1989, was the first space-based astrometric mission, and its precise measurements of parallax and proper motion have enabled much better measurements of the Oort constants. In 1997 Hipparcos data were used to derive the values ${\displaystyle A}$ = 14.82 ± 0.84 km s⁻¹ kpc⁻¹ and ${\displaystyle B}$ = -12.37 ± 0.64 km s⁻¹ kpc⁻¹. The Gaia spacecraft, launched in 2013, is an updated successor to Hipparcos; which allowed new levels of accuracy in measuring four Oort constants ${\displaystyle A}$ = 15.3 ± 0.4 km s⁻¹ kpc⁻¹, ${\displaystyle B}$ = -11.9 ± 0.4 km s⁻¹ kpc⁻¹, ${\displaystyle C}$ = -3.2 ± 0.4 km s⁻¹ kpc⁻¹ and ${\displaystyle K}$ = -3.3 ± 0.6 km s⁻¹ kpc⁻¹.

With the Gaia values, we find

${\displaystyle {\begin{aligned}&{\frac {dv}{dr}}{\Bigg \vert }_{R_{0}}=-A-B=-3.4{\text{ km/s/kpc}}\\&{\frac {V_{0}}{R_{0}}}=\Omega =A-B=27.2{\text{ km/s/kpc}}\\\end{aligned}}}$

This value of Ω corresponds to a period of 226 million years for the sun's present neighborhood to go around the Milky Way. However, the time it takes for the sun to go around the Milky Way (a galactic year) may be longer because (in a simple model) it is circulating around a point further from the centre of the galaxy where Ω is smaller.

The values in km s⁻¹ kpc⁻¹ can be converted into milliarcseconds per year by dividing by 4.740. This gives the following values for the average proper motion of stars in our neighborhood at different galactic longitudes, after correction for the effect due to the sun's velocity with respect to the local standard of rest:

Galactic longitude	Constellation	ave. proper motion	mas/ year	approximate direction
0°	Sagittarius	B+A	0.7	north-east
45°	Aquila	B	2.5	south-west
90°	Cygnus	B−A	5.7	west
135°	Cassiopeia	B	2.5	west
180°	Auriga	B+A	0.7	south-east
225°	Monoceros	B	2.5	north-west
270°	Vela	B−A	5.7	west
315°	Centaurus	B	2.5	west

The motion of the sun towards the solar apex in Hercules adds a generally westward component to the observed proper motions of stars around Vela or Centaurus and a generally eastward component for stars around Cygnus or Cassiopeia. This effect falls off with distance, so the values in the table are more representative for stars that are further away. On the other hand, more distant stars or objects will not follow the table, which is for objects in our neighborhood. For example, Sagittarius A*, the radio source at the centre of the galaxy, will have a proper motion of approximately Ω or 5.7 mas/y southwestward (with a small adjustment due to the sun's motion toward the solar apex) even though it is in Sagittarius. Note that these proper motions cannot be measured against "background stars" (because the background stars will have similar proper motions), but must be measured against more stationary references such as quasars. 

Meaning

Figure 3: Diagram of the various rotation curves in a galaxy

 

The Oort constants can greatly enlighten one as to how the Galaxy rotates. As one can see ${\displaystyle A}$ and ${\displaystyle B}$ are both functions of the Sun's orbital velocity as well as the first derivative of the Sun's velocity. As a result, ${\displaystyle A}$ describes the shearing motion in the disk surrounding the Sun, while ${\displaystyle B}$ describes the angular momentum gradient in the solar neighborhood, also referred to as vorticity.

To illuminate this point, one can look at three examples that describe how stars and gas orbit within the Galaxy giving intuition as to the meaning of ${\displaystyle A}$ and ${\displaystyle B}$. These three examples are solid body rotation, Keplerian rotation and constant rotation over different annuli. These three types of rotation are plotted as a function of radius (${\displaystyle R}$), and are shown in Figure 3 as the green, blue and red curves respectively. The grey curve is approximately the rotation curve of the Milky Way. 

Solid body rotation

To begin, let one assume that the rotation of the Milky Way can be described by solid body rotation, as shown by the green curve in Figure 3. Solid body rotation assumes that the entire system is moving as a rigid body with no differential rotation. This results in a constant angular velocity, ${\displaystyle \Omega }$, which is independent of ${\displaystyle R}$. Following this we can see that velocity scales linearly with ${\displaystyle R}$, ${\displaystyle v\propto r}$, thus

${\displaystyle {\begin{aligned}&{\frac {dv}{dr}}={\frac {v}{r}}=\Omega \\\end{aligned}}}$

Using the two Oort constant identities, one then can determine what the ${\displaystyle A}$ and ${\displaystyle B}$ constants would be,

${\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left({\frac {\Omega _{0}R_{0}}{R_{0}}}-{\Omega }{\Bigg \vert }_{R_{0}}\right)=0\\&B=-{\frac {1}{2}}\left({\frac {\Omega _{0}R_{0}}{R_{0}}}+{\Omega }{\Bigg \vert }_{R_{0}}\right)=-\Omega _{0}\\\end{aligned}}}$

This demonstrates that in solid body rotation, there is no shear motion, i.e. ${\displaystyle A=0}$, and the vorticity is just the angular rotation, ${\displaystyle B=-\Omega }$. This is what one would expect because there is no difference in orbital velocity as radius increases, thus no stress between the annuli. Also, in solid body rotation, the only rotation is about the center, so it is reasonable that the resulting vorticity in the system is described by the only rotation in the system. One can actually measure and find that is non-zero (${\displaystyle A=14}$ km s⁻¹ kpc⁻¹). Thus the galaxy does not rotate as a solid body in our local neighborhood, but may in the inner regions of the Galaxy. 

Keplerian rotation

The second illuminating example is to assume that the orbits in the local neighborhood follow a Keplerian orbit, as shown by the blue line in Figure 3. The orbital motion in a Keplerian orbit is described by,

${\displaystyle v={\sqrt {\frac {GM}{r}}}}$

where ${\displaystyle G}$ is the Gravitational Constant, and ${\displaystyle M}$ is the mass enclosed within radius ${\displaystyle r}$. The derivative of the velocity with respect to the radius is,

${\displaystyle {\frac {dv}{dr}}=-{\frac {1}{2}}{\sqrt {\frac {GM}{R^{3}}}}=-{\frac {1}{2}}{\frac {v}{r}}}$

The Oort constants can then be written as follows,

${\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}+{\frac {v}{2r}}{\Bigg \vert }_{R_{0}}\right)={\frac {3V_{0}}{4R_{0}}}\\&B=-{\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}-{\frac {v}{2r}}{\Bigg \vert }_{R_{0}}\right)=-{\frac {1V_{0}}{4R_{0}}}\\\end{aligned}}}$

For values of Solar velocity, ${\displaystyle V_{0}=218}$ km/s, and radius to the Galactic center, ${\displaystyle R_{0}=8}$ kpc,^[4] the Oort's constants are ${\displaystyle A=20}$ km s⁻¹ kpc⁻¹, and ${\displaystyle B=-7}$ km s⁻¹ kpc⁻¹. However, the observed values are ${\displaystyle A=14}$ km s⁻¹ kpc⁻¹ and ${\displaystyle B=-12}$ km s⁻¹ kpc⁻¹. Thus, Keplerian rotation is not the best description the Milky Way rotation. Furthermore, although this example does not describe the local rotation, it can be thought of as the limiting case that describes the minimum velocity an object can have in a stable orbit. 

Flat rotation curve

The final example is to assume that the rotation curve of the Galaxy is flat, i.e. ${\displaystyle v}$ is constant and independent of radius, ${\displaystyle r}$. The rotation velocity is in between that of a solid body and of Keplerian rotation, and is the red dottedline in Figure 3. With a constant velocity, it follows that the radial derivative of ${\displaystyle v}$ is 0,

${\displaystyle {\frac {dv}{dr}}=0}$

and therefore the Oort constants are,

${\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}-0{\Bigg \vert }_{R_{0}}\right)={\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}\right)\\&B=-{\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}+0{\Bigg \vert }_{R_{0}}\right)=-{\frac {1}{2}}\left({\frac {V_{0}}{R_{0}}}\right)\\\end{aligned}}}$

Using the local velocity and radius given in the last example, one finds ${\displaystyle A=13.6}$ km s⁻¹ kpc⁻¹ and ${\displaystyle B=-13.6}$ km s⁻¹ kpc⁻¹. This is close to the actual measured Oort constants and tells us that the constant-speed model is the closest of these three to reality in the solar neighborhood. But in fact, as mentioned above, ${\displaystyle -A-B}$ is negative, meaning that at our distance, speed decreases with distance from the centre of the galaxy. 

What one should take away from these three examples, is that with a remarkably simple model, the rotation of the Milky Way can be described by these two constants. The first two examples are used as constraints to the Galactic rotation, for they show the fastest and slowest the Galaxy can rotate at a given radius. The flat rotation curve serves as an intermediate step between the two rotation curves, and in fact gives the most reasonable Oort constants as compared to current measurements. 

Uses

One of the major uses of the Oort constants is to calibrate the galactic rotation curve. A relative curve can be derived from studying the motions of gas clouds in the Milky Way, but to calibrate the actual absolute speeds involved requires knowledge of V₀. We know that:

${\displaystyle V_{0}=R_{0}(A-B)\,\!}$

Since R₀ can be determined by other means (such as by carefully tracking the motions of stars near the Milky Way's central supermassive black hole), knowing ${\displaystyle A}$ and ${\displaystyle B}$ allows us to determine V₀.

It can also be shown that the mass density ${\displaystyle \rho _{R}}$ can be given by:

${\displaystyle \rho _{R}={\frac {B^{2}-A^{2}}{2\pi G}}}$

So the Oort constants can tell us something about the mass density at a given radius in the disk. They are also useful to constrain mass distribution models for the Galaxy. As well, in the epicyclic approximation for nearly circular stellar orbits in a disk, the epicyclic frequency ${\displaystyle \kappa }$ is given by ${\displaystyle \kappa ^{2}=-4B\Omega }$, where ${\displaystyle \Omega }$ is the angular velocity. Therefore, the Oort constants can tell us a great deal about motions in the galaxy.