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Main Sequence

Main sequence

The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. Stars located on this band are known as main-sequence stars or dwarf stars. The coolest dwarfs are the red dwarfs. This line is so pronounced because both the spectral type and the luminosity depend on a star's mass only to zeroth order as long as it is fusing hydrogen—and that is what almost all stars spend most of their "active" life doing. At closer inspection, one notices that the main sequence is not exactly a line but instead somewhat fuzzy. There are many reasons for this fuzziness, the most important one still being observational uncertainties which mainly affect the distance of the star in question but range all the way to unresolved binary stars. But even perfect observations would lead to a fuzzy main sequence, because mass, after all, is not the only parameter a star has. Chemical composition and—related—its evolutionary status also move a star slightly on the main sequence, as do close companions, rotation, or magnetic fields, to name just a few. Actually, there are very metal-poor stars (subdwarfs) that lie just below the main sequence although they are fusing hydrogen, thus marking the lower edge of the main sequence's fuzziness due to chemical composition. Astronomers will sometimes refer to the "zero age main sequence", or ZAMS. This is a line calculated by computer models of where a star will be when it begins hydrogen fusion. Stars usually enter and leave the main sequence from about when they are born or when they are starting to die, respectively. Our Sun is a main-sequence star—it has been one for about 4.5 billion years and will continue to be one for another 4.5 billion years. It has the spectral classification of G2 V. After the hydrogen supply in the core is exhausted, it will expand to become a red giant.

Main sequence data

The table below shows typical values for stars along the main sequence. The values of luminosity (L), radius (R), and mass (M) are relative to the Sun. The actual values for a star may vary by as much as 20-30%. The coloration of the stellar class column gives an approximate representation of the star's photographic color. :

In the arts

Main sequence is also the name of a composition of music by composer Vangelis on his 1976 album, Albedo 0.39 and is in reference to the astronomical term.

External links

- [http://www.io.com/~iareth/mainsequence.html Table of Features of the "Life Zones" of Main Sequence Stars]
- Category:Stellar evolution ja:主系列星

Curve

In mathematics, the concept of a curve tries to capture the intuitive idea of a geometrical one-dimensional and continuous object. Simple examples are the circle or the straight line. A large number of other curves have been studied in geometry. This article is about the general theory. The term curve is also used in ways making it almost synonymous with mathematical function (as in learning curve), or graph of a function (Phillips curve).

Definitions

In mathematics, a (topological) curve is defined as follows. Let

I

be an interval of real numbers (i.e. a non-empty connected subset of

\mathbb

). Then a curve

\!\,\gamma

is a continuous mapping

\,\!\gamma : I \rightarrow X

, where

X

is a topological space. The curve

\!\,\gamma

is said to be simple if it is injective, i.e. if for all

x

y

I

, we have

\,\!\gamma(x) = \gamma(y) \rightarrow x = y

. If

I

is a closed bounded interval

\,\![a, b]

, we also allow the possibility

\,\!\gamma(a) = \gamma(b)

(this convention makes it possible to talk about closed simple curve). If

\gamma(x)=\gamma(y)

for some

x\ne y

(other than the extremities of

I

), then

\gamma(x)

is called a double (or: multiple) point of the curve. A curve

\!\,\gamma

is said to be closed or a loop if

\,\!I = [a, b]

and if

\!\,\gamma(a) = \gamma(b)

. A closed curve is thus a continuous mapping of the circle

S^1

; a simple closed curve is also called a Jordan curve. A plane curve is a curve for which X is the mathematical plane — these are the examples first encountered — or in some cases the projective plane. A space curve is a curve for which X is of three dimensions, usually Euclidean space; a skew curve is a space curve which lies in no plane. These definitions also apply to algebraic curves (see below). This definition of curve captures our intuitive notion of a curve as a connected, continuous geometric figure that is "like" a line, although it also includes figures that can be hardly called curves in common usage. For example, the image of a curve can cover a square in the plane (Peano curve). The image of simple plane curve can have Hausdorff dimension bigger than one (see Koch snowflake) and even positive Lebesgue measure (the last example can be obtained by small variation of the Peano curve construction). The dragon curve is yet another weird example.

Conventions and terminology

The distinction between a curve and its image is important. Two distinct curves may have the same image. For example, a line segment can be traced out at different speeds, or a circle can be traversed a different number of times. Many times, however, we are just interested in the image of the curve. It is important to pay attention to context and convention in reading. Terminology is also not uniform. Often, topologists use the term "path" for what we are calling a curve, and "curve" for what we are calling the image of a curve. The term "curve" is more common in vector calculus and differential geometry.

Length of curves

X

is a metric space with metric

d

, then we can define the length of a curve

\!\,\gamma : [a, b] \rightarrow X

by :

\mbox (\gamma)=\sup \left\

A rectifiable curve is a curve with finite length. A parametrization of

\!\,\gamma

is called natural (or unit speed or parametrised by arc length) if for any

t_1

t_2

[a, b]

, we have :

\mbox (\gamma|_)=|t_2-t_1|

\!\,\gamma

is Lipschitz then it is automatically rectifiable. Moreover, in this case, one can define speed of

\!\,\gamma

t_0

as :

\mbox(t_0)=\limsup_

and then :

\mbox(\gamma)=\int_a^b \mbox(t) \, dt

In particular, if

X = \mathbb^n

is Euclidean space and

\gamma : [a, b] \rightarrow \mathbb^n

is differentiable then :

\mbox(\gamma)=\int_a^b \left| \,  \, \right| \, dt

Differential geometry

Main article: differential geometry of curves While the first examples of curves that are met are mostly plane curves (that is, in everyday words, curved lines in two-dimensional space), there are obvious examples such as the helix which exist naturally in three dimensions. The needs of geometry, and also for example classical mechanics are to have a notion of curve in space of any number of dimensions. In general relativity, a world line is a curve in spacetime. If

X

is a differentiable manifold, then we can define the notion of differentiable curve in

X

. This general idea is enough to cover many of the applications of curves in mathematics. From a local point of view one can take

X

to be Euclidean space. On the other hand it is useful to be more general, in that (for example) it is possible to define the tangent vectors to

X

by means of this notion of curve. If

X

is a smooth manifold, a smooth curve in

X

is a smooth map :

\!\,\gamma : I \rightarrow X.

This is a basic notion. There are less and more restricted ideas, too. If

X

is a

C^k

manifold (i.e., a manifold whose charts are

k

times continuously differentiable), then a

C^k

curve in

X

is such a curve which is only assumed to be

C^k

(i.e.

k

times continuously differentiable). If

X

is an analytic manifold (i.e. infinitely differentiable and charts are expressible as power series), and

\!\,\gamma

is an analytic map, then

\!\,\gamma

is said to be an analytic curve. A differentiable curve is said to be regular if its derivative never vanishes. (In words, a regular curve never slows to a stop or backtracks on itself.) Two

C^k

differentiable curves :

\!\,\gamma_1 :I \rightarrow X

and :

\!\,\gamma_2 : J \rightarrow X

are said to be equivalent if there is a bijective

C^k

map :

\!\,p : J \rightarrow I

such that the inverse map :

\!\,p^ : I \rightarrow J

is also

C^k

, and :

\!\,\gamma_(t) = \gamma_(p(t))

for all

t

. The map

\!\,\gamma_2

is called a reparametrisation of

\!\,\gamma_1

; and this makes an equivalence relation on the set of all

C^k

differentiable curves in

X

. A

C^k

arc is an equivalence class of

C^k

curves under the relation of reparametrisation.

Algebraic curve

Main article: Algebraic curve In the setting of algebraic geometry, a curve is usually defined to be an algebraic curve. These include, for example, elliptic curves, which are studied in number theory and which have important applications to cryptography. Algebraic curves are more akin to surfaces than curves. Non-singular complex projective algebraic curves are in fact compact Riemann surfaces.

History

A curve may be a locus, or a path. That is, it may be a graphical representation of some property of points; or it may be traced out, for example by a stick in the sand on a beach. Of course if one says curved in ordinary language, it means bent (not straight), so refers to a locus. This leads to the general idea of curvature. As we now understand, after Newtonian dynamics, to follow a curved path a body must experience acceleration. Before that, the application of current ideas to (for example) the physics of Aristotle is probably anachronistic. This is important because major examples of curves are the orbits of the planets. One reason for the use of the Ptolemaic system of epicycle and deferent was the special status accorded to the circle as curve. The conic sections had been deeply studied by Apollonius of Perga. They were applied in astronomy by Kepler. The Greek geometers had studied many other kinds of curves. One reason was their interest in geometric constructions, going beyond ruler-and-compass constructions. In that way, the intersection of curves could be used to solve some polynomial equations, such as that involved in trisecting an angle. Newton also worked on an early example in the calculus of variations. Solutions to variational problems, such as the brachistochrone and tautochrone questions, introduced properties of curves in new ways (in this case, the cycloid). The catenary gets its name as the solution to the problem of a hanging chain, the sort of question that became routinely accessible by means of differential calculus. In the eighteenth century came the beginnings of the theory of plane algebraic curves, in general. Newton had studied the cubic curves, in the general description of the real points into 'ovals'. The statement of Bézout's theorem showed a number of aspects which were not directly accessible to the geometry of the time, to do with singular points and complex solutions. From the nineteenth century there is not a separate curve theory, but rather the appearance of curves as the one-dimensional aspect of projective geometry, and differential geometry; and later topology, when for example the Jordan curve theorem was understood to lie quite deep, as well as being required in complex analysis. The era of the space-filling curves finally provoked the modern definitions of curve.

External links

- [http://www-gap.dcs.st-and.ac.uk/~history/Curves/Curves.html List of famous curves] Category:Curves Category:Metric geometry Category:Topology Category:General topology ko:곡선 ja:曲線

Red Dwarf

:This article describes the British science fiction comedy television series. For the type of star, see red dwarf. red dwarf Red Dwarf is a science fiction Britcom (British situational comedy) created and originally written by Grant Naylor (the pseudonym for the "gestalt entity" comprised of the writing duo Rob Grant and Doug Naylor). It tells the story of Dave Lister, the last human being, and takes place 3 million years in the future aboard the Jupiter Mining Corporation's ore transport vessel Red Dwarf, a spaceship the size of a city. A pastiche of science fiction in general, Red Dwarf is first and foremost an 'odd couple' type situational comedy, which may itself seem odd, raising the question "If Dave Lister is the last surviving human, who is he paired with?" Well, a holosimulation of his dead bunk mate, Arnold Judas Rimmer, of course.

Scenario

'odd couple' In the show, the Red Dwarf is a spaceship the size of a city belonging to the Jupiter Mining Corporation. An on-board radiation leak kills everyone except for Dave Lister, who was in suspended animation at the time, and his pregnant cat. Three million years later, Lister emerges from stasis as the last human being alive. Lister is the lowest ranking employee on the ship. He is the slob anti-hero with a marked Scouse accent and an obsession with Indian food, such as vindaloo, curries, and shami kebabs, all of which are in plentiful supply on board the ship. He also enjoys a type of music called "Rastabilly Skank," playing the guitar, and singing -- much to the detriment of those around him. His goal in life (before he goes into stasis) was to buy a farm in Fiji, buy a sheep and a cow, and raise horses because property in Fiji is cheap. Rimmer states that Fiji is mostly below water due to volcanic activity, but Lister replies that it's just three feet in some places and they can wade in that. He has other plans that revolve around Fiji that he tells his cat such as a doughnut and hotdog shop and being with Kristine Kochanski. Lister endures a hologramatic simulation of a deceased crew member Arnold J. Rimmer. Rimmer, Lister's room-mate before the disaster, is a smug, self-serving, mean-spirited, status-obsessed, neurotic, guilt-ridden loser, loathed by everybody on board. Despite fourteen years aboard the ship and an overriding ambition to become an officer, Rimmer has sat and failed his astro-navigation exam on no less than 11 occasions. On one occasion he even wrote 'I am a fish' four hundred times, did a funny little dance and fainted. On another he copied answers onto his arm to cheat, but to his horror his nervous sweat had smeared the ink when he rolled up his sleeve to look at them; he took the hand he smeared ink upon, put it on the answer sheet to leave a hand print, saluted to examiner, and fainted. Even after all this, Rimmer remains a chicken soup-machine repairman, the second lowest ranking job aboard the ship. It was he who actually (unintentionally) caused the radiation leak by poorly repairing a drive plate on the power core, though he claims he would have been able to do a better job if Lister had not been imprisoned in stasis. The facility for simulating dead crew members is so resource-intensive that only one such simulation can be maintained at a time. It is therefore reserved for high-ranking and/or essential personnel, but the ship's computer explains in an early episode that it believes Rimmer's company to be essential keeping Lister sane. Lister expresses incredulity, but later implicitly admits that the computer was right, telling another character, Kryten the mechanoid, that "driving Rimmer nuts is what keeps me going". As the show progresses, Rimmer acquires a tangible physical form for brief periods of time due to various astronomical phenomena, and eventually acquires a "hard-light drive", giving him an effectively real -- albeit almost indestructible -- physical presence. In other episodes, Rimmer is also manifested as the superheroic character, Ace Rimmer, who hails from a parallel universe where a pivotal humiliation led Rimmer to develop into a James Bond-like persona. Also accompanying Lister on his voyage back to Earth is The Cat. Cat is of the species Felis sapiens, evolved from a pregnant domestic cat named Frankenstein which Lister had smuggled aboard the ship three million years prior, the crime which Lister was imprisoned in stasis for committing. The Cat appears as a typical biped humanoid with slightly elongated feline teeth; he retains a cat-like features including a craving for fish and females, a heightened sense of smell, unbridled vanity, the requirement to nap multiple times a day, an obsession towards grooming and appearance, and six nipples. Multiple jokes in the show involve his "cool" nature, including an incident in which it is revealed that his heartbeat is actually a catchy bassline, and the recurring anti-Cat role of Dwayne Dibley. Lister was deemed a god by the Cat race (despite the fact that the pictures of the Cat God looks like Rimmer and has a visibly large H on his forehead), and Frankenstein was called "The Holy Mother" who started the cat society with a virgin birth. Their holy book stated that Cloister (Lister) would take them to Fuchal (Fiji) to open a hotdog and doughnut shop; this was their idea of heaven. The Cats eventually diverged into two sects: those who thought the workers at the shop would wear red hats, and those who thought they would wear blue. Much death was cause from this split and they eventually left in arks using Lister's laundry list as coordinates to find Fuchal; one crashed, and the other is said to still be flying through space. After hearing this, Lister said that the hats were supposed to be green. The other principal character is Holly, the ship's computer with a supposed IQ of 6000, which Holly claims is the same IQ as 6000 P.E. (sports) teachers. Holly is visible as a disembodied head on the screens dotted around the ship and runs most of the ship's systems despite now suffering from computer senility. Among Holly's systems are the semi-autonomous service droids known as the skutters that clean, perform engineering tasks, and function as Rimmer's hands (even though they don't like him) since he initially cannot touch anything non-holographic; the skutters are also slightly computer senile and have developed personality quirks such as an affinity for John Wayne movies. The crew are also joined by the service mechanoid Kryten after rescuing him from a crashed vessel, the Nova 5. Kryten immediately takes over custodial duties on Red Dwarf. While Rimmer basks in subjugating Kryten, Lister befriends Kryten and encourages him to break his altruistic programming to lie, cheat, and steal in an effort to become more human. Kryten at one time did in fact break his programming, "borrowed" Lister's space-bike and left the ship. He was found smashed against an asteroid some light-years away, and was rebuilt with a new personality and altered appearance. Kryten offers encyclopedic knowledge in all areas and is generally Red Dwarf's voice of reason; however, he can become hilariously unpredictable when Lister swaps Kryten's head for one of the eager, jealous "spare heads" or removes Kryten's morality chip. Lister's longlasting crush is Kristine Kochanski, played by C. P. (Clare) Grogan (formerly of 1980s band Altered Images). She was killed along with the rest of the crew in the first episode, and several subsequent episodes revolve around Lister attempting to bring her back, either through time travel or as a computer-generated simulation like Rimmer. In various TV series and book incarnations, Lister has either admired Kochanski from afar or dated her for over a month. The discontinuity is never touched upon. In the seventh season, an alternative Kochanski from a parallel universe (played by Chloë Annett) joined the series as a regular character. One interesting aspect of the Red Dwarf universe that differentiates it from standard science fiction is that there are no sentient aliens; instead, every part of the large and bizarre mix of intelligent life within the Red Dwarf universe is in one way or another derived from Earth, a result of developments in robotics and/or genetic engineering during the millions of years the ship has been isolated.

Production history

The first series aired on BBC2 in 1988. Seven further series have so far been produced, and a film is currently in pre-production. The idea was originally developed from the Dave Hollins: Space Cadet sketches introduced on Grant and Naylor's 1984 BBC Radio 4 show Son of Cliché. Rob Grant and Doug Naylor wrote the first six series together, before Grant left in 1996 leaving Naylor to write the next two with a series of new and less well-known writers, notably Paul Alexander. For the most part, Ed Bye produced and directed the series. He left before Series V, and Juliet May took over as director, but she was dismissed partway through the season and replaced by Grant and Naylor. Series VI was directed by Andy DeEmmony, with Bye returning for the final two series. Series I and II were BBC productions, series III was made by Paul Jackson Productions, and all subsequent series were made by Grant Naylor Productions; all eight series were broadcast by the BBC. At the beginning of series IV production moved from the BBC's Manchester studios to Shepperton. The theme tune and incidental music were written by Howard Goodall and performed by Jenna Russell. Goodall also provided the musical accompaniment for the chart hit 'Tongue Tied', which was written by Danny John-Jules. Craig Charles wrote, performed and sang 'He's got Cash' from the episode 'Timeslides'. A period of four years elapsed between Series VI and VII. The show was apparently not expected to last beyond five series, indicated by the closure of major plot elements and continuity during the first two series. However, Grant and Naylor were contractually obliged to make eight series for the BBC. When the series returned, it was filmized and no longer in front of a live audience. Although critics praised the higher production values for Series VII, when the show returned two years later for Series VIII, it had dropped use of the filmizing process. In 1998, on the tenth anniversary of the show's first airing (between the releases of Series VII and VIII), the first three series of Red Dwarf were remastered. The remastering included reformatting the series in widescreen, applying film grain techniques and more critically replaced model shots with computer graphics, cut small pieces of dialog and changed music and sound effects. Red Dwarf Remastered was met with a generally poor fan reaction, no further series were remastered and the later DVD release reverted to the original versions.

Episode list

See List of Red Dwarf episodes.

Characters and actors

:Main article: Red Dwarf characters

Regular cast

- Dave Lister (played by Craig Charles, also known for Robot Wars and a variety of other British shows.)
- Arnold Rimmer (played by Chris Barrie, also known for his starring role in The Brittas Empire, numerous voices on Spitting Image, and his role as Lara Croft's butler in the Tomb Raider movies.)
- The Cat (played by Danny John-Jules, who has appeared in Lock, Stock and Two Smoking Barrels, Gulliver's Travels, and Blade II.)
- Holly (played by Norman Lovett in series 1, 2, 7 and 8, and by Hattie Hayridge in series 3, 4 and 5, who has appeared in Lexx playing "Sub-Warden Heidi" in episode "P4X" (episode #4.3).)
- Kryten (played by David Ross in his first appearance in series 2, and by Robert Llewellyn in series 3 through 8. Robert Llewellyn is also known for Scrapheap Challenge (aka Junkyard Wars in the USA).)
- Kristine Kochanski (played by C. P. (Clare) Grogan in series 1, 2 and 6, and by Chloë Annett in series 7 and 8. Claire Grogan was the lead singer of Altered Images in the 1980s. Chloë Annett is also known for Crime Traveller.)

Recurring guest characters

- Captain Frank Hollister (played by Mac McDonald) appears in series 8, two episodes of series 1 and one episode of series 2.
- Olaf Petersen (played by Mark Williams) appeared in three episodes and is mentioned regularly when Lister talks about the days before the accident.
- Selby and Chen (played by David Gillespie and Paul Bradley, respectively) appeared in three episodes altogether.
- Frank Todhunter (played by Robert Bathurst) only appeared in the first episode but was regularly mentioned in following episodes.
- George McIntyre, a Welsh officer, appeared once in the first episode as a hologram at his own "Welcome Back Reception".
- Kill Crazy (played by Jake Wood) appeared in four episodes of series 8.
- Warden Ackerman (played by Graham McTavish) appears in series 8.
- Baxter (played by Ricky Grover) appeared in the last three episodes of series 8.

Recurring guest actors

- Tony Hawks was the warm-up man for the first few series of Red Dwarf and has often been called 'The Fifth Dwarfer'. He also appeared on screen as the host in Better Than Life, the voice of various food dispensers (and a talking suitcase in Stasis Leak), the compere in Backwards, and Caligula in Meltdown.

Ships

:Main article: Red Dwarf ships

Red Dwarf

Red Dwarf ships The main ship after which the show is named. Red Dwarf is five miles long, not including the scoop at the front, and can hold over a thousand crew members. It also holds a complement of Starbug and Blue Midget shuttlecrafts. The "scoop" at the front of the ship collects trace hydrogen gases from space and converts them into fuel: the ship, therefore, could theoretically keep on travelling forever. As a mining vessel, the Red dwarf has massive bays which apparently holds large asteroids in place for mining. Currently the ship is holding onto one such asteroid, though this does not appear to affect the ship's integrity. Red Dwarf was redesigned for the remastered series, making it even longer and more streamlined, with multiple smaller engines at the rear, as opposed to the singular long engine used on previous models. This design did not stick but was re-used in Series 8, after Red Dwarf's reconstruction by the nanobots, complete with Karaoke deck.

Blue Midget

remastered series Blue Midget is a type of shuttle that Red Dwarf carries, and was the primary craft in series 2 before being replaced by Starbug. It is built to resemble a truck or tank, with caterpillar tracks and a bumper sticker. Blue Midget was redesigned in the remastered series to resemble a bubble car with retractable legs for "walking", and this design was also used for Series 8 (for the original episodes continuity, it is feasible that when Red Dwarf was reconstructed slightly differently the same thing happened to the Blue Midgets aboard the ship).

Starbug

remastered series The JMC transport vehicle Starbug is the model of a small shuttle craft, green in colour. It has three bulbous sections; the cockpit, mid-section and engine rooms, somewhat resembling a bug from the exterior. Starbug replaced Blue Midget as the crew's primary choice of shuttle in series 3 and became the show's primary vehicle thoughout series 6 and 7. Series 6 takes place a full 200 years after the final episodes of series 5. During this time it is presumed that Kryten remodelled Starbug to better suit the crews needs, being the only one not in deep-sleep. Starbug's remodelling, along with a time-dilation effect, expanded the ship's interior dimensions and produced an additional sleeping quarters, engine deck and hangar bay. In episode 6.3 Starbug was finally armed with laser cannons by rogue simulants.

US version

A pilot episode for an American version was produced for NBC in 1992, though never broadcast. The show followed essentially the same story as the original UK pilot, substituting American actors (including Craig Bierko as Lister, Chris Eigeman as Rimmer, and Hinton Battle as the Cat) for the British; exceptions being Robert Llewellyn, who reprised his role as Kryten and the British actress Jane Leeves who took the part of Holly. The pilot was unsuccessful. A later pilot consisting of scenes from the first pilot edited in with new footage (and featuring Terry Farrell as a female Cat) was also unsuccessful. However, the comparison between the UK and US shows is interesting: the anti-hero, slobby pantheist Lister was replaced with a muscular hunk when he is translated for American TV. When Lister learns that three million years have passed in the UK show, he says "I've still got that library book..."; in the American version he says "My baseball cards must be worth a fortune!" It is also interesting to note that the multi-ethnic cast of the British original (John-Jules is black, Charles bi-racial, and Barrie and Llewelyn white) was replaced by an entirely Caucasian one for the second US pilot (the first pilot still had a black Cat), leading John-Jules and Charles to dub it 'White Dwarf'. Clips from the first pilot can be found on the DVD of Series 5 in the featurette Dwarfing USA, along with interviews with the British cast and Doug Naylor. Bootlegs of the pilots are widely circulated among Red Dwarf fans, and sold at conventions.

Spin-offs

The franchise has expanded to include four novels, written by the show's creators, Doug Naylor and Rob Grant.
- Red Dwarf: Infinity Welcomes Careful Drivers - Grant Naylor - ISBN 0-45-145201-1
- Better Than Life - Grant Naylor - ISBN 0-14-012438-1
- Last Human - Doug Naylor - ISBN 0-14-014388-2
- Backwards - Rob Grant - ISBN 0-14-017150-9 The first book, Red Dwarf, had cover art that could be interpreted as saying Infinity Welcomes Careful Drivers is the title, and the book is often called this to distinguish it from other incarnations. Due to various reasons, Grant and Naylor decided to both work alone when writing the sequel to Better Than Life, and so two completely different sequels were made. Last Human (by Doug Naylor, who would go on to make two further television series) introduced Kochanski to unsuspecting fans and felt very much like series seven of the TV programme, while Backwards (by Rob Grant) was more in keeping with the previous two books. The styles in both sequels vary wildly to each other and the two predecessors. Many fans believe that both novels are far inferior to the two books written in collaboration. All four books contain well-loved elements from certain episodes of the television series. Infinity Welcomes Careful Drivers contained lines and story elements from The End, Future Echoes, Kryten, Me² and Better Than Life. Better Than Life contained elements from Better Than Life, Marooned, Polymorph and Backwards (the "playing pool with planets" sub-plot was written before the White Hole TV episode). Last Human contained elements from Backwards, Polymorph II: Emohawk and DNA. The novel Backwards contained elements from Backwards (obviously), Dimension Jump and Gunmen of the Apocalypse. While these elements are taken from the original source material, they were cleverly enhanced (and often improved) to fit in with the overall plots of every book due to not being inhibited by budgetry constraints. All four books were published in audiobook format, the first two read by Chris Barrie with Last Human read by Craig Charles and Backwards read by its author Rob Grant. The BBC World Service re-recorded the first two books as The Red Dwarf Radio Show with Chris Barrie narrating and included additional sound effects. The first series was broadcast on 3 December 1995 to 17 February 1996 and the second March 13 1997 to March 28 1997. The song "Tongue Tied", originally featured in a dream sequence in the episode Parallel Universe, was released as a single in 1993. It reached number 17 in the UK charts. It was expected to get higher, only a planned Top Of The Pops performance did not come to happen, thus halting momentum for the single. A planned Red Dwarf: The Movie has been delayed from its original schedule. According to the official website, it will enter pre-production 'shortly', with details of a release date to follow. Unfortunately it has been over a year since any news has been heard regarding the movie.

Invented words

Red Dwarf famously employed a vocabulary of fictional expletives in order to avoid using potentially-offensive expletives in the show, and to give nuance to futuristic colloquial language. By far, the most famous example is smeg. Variations of the word include: smegger, smeghead, smeg off, smeg-for-brains, and smegging hell; it is used as a synonym for the word fuck. In one episode, Rimmer tells a vending machine to "smeg off, you smeggy smegging smegger!"; another episode features the phrase "Oh smeg, what the smegging smeg's he smegging done? He's smegging killed me!". The writers of Red Dwarf have stated that they invented the word and that it has no connection with any similar real words, such as smegma; however, lexicographer Tony Thorne, in his 1990 Dictionary of Contemporary Slang (ISBN 074752856X), reports instances of smeg (and derivatives) being used as a term of "mild contempt and even affection" among "schoolboys, students and punks" as early as the mid-1970s—a decade or so prior to the inception of the Red Dwarf phenomenon—and unequivocally traces the etymology of the term back to smegma. Other fictional expletives and euphemisms include goit (one who is annoying or awkward; perhaps adapted from the words git and oik; a synonym for the word cunt) and gimboid (one who is stupid or clumsy; possibly an adaptation of the word gimp). Another term of abuse used in the show was the word Gwendolin, the last name of Gareth Gwenlan who was the head of comedy for the BBC and passed on the show in London. The currency in use at the time Red Dwarf left the Solar System was apparently the "dollarpound", divided into one hundred "pennycents". In one episode, Cat plays the word jozxyqk in a game of Scrabble, claiming it to be a cat word meaning "the sound you get when you get your sexual organs trapped in something." However, this is most likely an attempt by Cat to use otherwise useless letters in a game he may well have been losing. Red Dwarf establishes that, in its fictional universe, the evolved Cat species does not have a written language, and instead records information as a scent. Therefore, it seems unlikely that jozxyqk is a Cat word. A class of beings that makes recurring appearances in the programme are GELFs, an acronym for Genetically Engineered Life Forms. Several sets, seen often in the earlier episodes, have the phrase "Level Nivelo" prominently displayed on one wall. "Nivelo" is not an invented word within the series, but rather the Esperanto word for "level". In the Red Dwarf universe, the constructed language Esperanto is in much wider use than it is today, and Red Dwarf is officially a bilingual vessel. See the first episode in season two, "Kryten", in which Rimmer attempts to learn Esperanto. In fact, all the Esperanto used in Red Dwarf is correct, if sometimes poorly pronounced - and in the books, incorrectly spelt or mis-printed. In the episode "Back To Reality", Timothy Spall's character Andy refers to the regular cast as "a bunch of twonks". Twonk is also used by Del Boy in Only Fools and Horses. He often calls Rodney a "dozy little twonk". "Twonk" has been around for a while is used by Frederick R. Ewing in the 1956 novel I, Libertine. The character Lance Courtney refers comedically to the acne in another character as being "Twonk's disease". In the Series 5 episode "The Inquisitor", Kryten refers to a statement made by Lister as "complete and utter shash", leaving the viewer to assume that "shash" is synonymous with "nonsense". This word however seems not to make any other appearances. Holly also uses the word "Hotspur" to mean nonsense ("Queeg") - this is clearly a reference to the London football team Tottenham Hotspur. Whilst on his own for three million years, Red Dwarf's computer, Holly, decided to entertain himself by inventing Hol Rock, a fictional decimalised version of music. The notes he invented were 'H' and 'J' and he was convinced it would be a whole new sound. Unfortunately triangles would need an extra side, pianos would be the length of zebra crossings and women would be banned from playing the cello.

Talking Backwards

In the season three episode "Backwards", there are several segments of reversed dialogue. Some of these are simply reversed recordings of the subtitled dialogue (a few with rather more "robust" language than the subtitled version), others are actors attempting (quite successfully) to speak backwards. An example of this is seen at the bar in the pub, where Lister discovers he has to order "Erskib" - played backwards, this really does sound like "Bitter". The longest backwards dialogue, however, is rather different. When the nightclub owner bursts in to sack Rimmer and Kryten, because of a fight (which hasn't happened yet, of course), Arthur Smith isn't actually saying what Kryten is translating. What he is really saying is: "You are a stupid, square-headed, bald git, aren't you? Eh? I'm pointing at you, I'm pointing at you. But I'm not actually addressing you. I'm addressing the one prat in the country who's bothered to get hold of this recording, turn it round, and actually work out the rubbish that I'm saying. What a poor sad life he's got."

Groovy Funky Channel 27

Groovy Funky Channel 27 (Although it may only be Channel 27, as Rimmer challenges Lister to name a famous hologram, Lister replies that Channel 27 has a hologram reading the news. Rimmer then mockingly, as well as with a sarcastic dance says "Groovy Funky Channel 27." Leading one to believe that he was simply making fun of Channel 27 and not actually naming it.) is a fictional TV news channel which appears on some episodes. The main news anchor is dead, and appears as a hologram with the letter H on her forehead (like Arnold Rimmer's). In one of the episodes, the Tv news channel claims that a new page of the bible had recently been discovered, which read, To my darling, Candy. All characters portrayed in this book are purely fictitious, and any likeness to anyone alive or dead is purely coincidental.

External links

- [http://www.faqs.org/faqs/tv/red-dwarf/faq/ Red Dwarf FAQ]
- [http://www.reddwarf.co.uk/ Red Dwarf site]
- [http://uk.imdb.com/Title?0276447 Entry for Red Dwarf: The Movie] in the Internet Movie Database
- [http://www.reddwarffanclub.com/ Red Dwarf Fan Club]
- [http://www.sadgeezer.com/html/Sections+index-req-viewarticle-artid-139-page-1.html The SadGeezers guide to Red Dwarf] Episodes, characters, ships and culture guides and resources
- [http://www.sitcom.co.uk/red_dwarf/ British Sitcom Guide]
- Red Dwarf transcripts http://www.reddwarf.nildram.co.uk/rd-seasons.htm
- [http://www.the7thlevel.com/archives/000113.php 25 Reasons You Should Watch Red Dwarf on The 7th Level]

Cast Links

- [http://www.normanlovett.co.uk/norman.htm Norman Lovett's (Holly's) Website]
- [http://www.llew.co.uk/ Robert Lewellyn's (Kryten's) Website]
- [http://www.chrisbarrie.co.uk/ Chris Barrie's (Rimmer's) Website] Category:Science fiction television series Category:British television sitcoms Category:BBC television programmes Category:Fictional spacecraft Category:Programs broadcast by YTV

Stellar classification

In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. Stellar temperatures can be classified by using Wien's displacement law; but this poses difficulties for distant stars. Stellar spectroscopy offers a way to classify stars according to their absorption lines; particular absorption lines can be observed only for a certain range of temperatures because only in that range are the involved atomic energy levels populated. An early schema (from the 19th century) ranked stars from A to P, which is the origin of the currently used spectral classes.

Morgan-Keenan spectral classification

This stellar classification is the most commonly used. The common classes are normally listed from hottest to coldest, and are:
- 1 = Sun. Values are averages. Sun] A popular mnemonic for remembering the order is "Oh Be A Fine Girl, Kiss Me" (there are many variants of this mnemonic). This scheme was developed in the 1900s, by Annie J. Cannon and the Harvard College Observatory. The Hertzsprung-Russell diagram relates stellar classification with absolute magnitude, luminosity, and surface temperature. It should be noted that while these descriptions of stellar colors are traditional in astronomy, they really describe the light after it has been scattered by the atmosphere. The Sun is not in fact a yellow star, but has essentially the color temperature of a black body of 5780 K; this is a white with no trace of yellow which is sometimes used as a definition for standard white. The reason for the odd arrangement of letters is historical. When people first started taking spectra of stars, they noticed that stars had very different hydrogen spectral lines strengths, and so they classified stars based on the strength of the hydrogen balmer series lines from A (strongest) to Q (weakest). Other lines of neutral and ionized species then came into play (H&K lines of calcium, sodium D lines etc). Later it was found that some of the classes were actually duplicates and those classes were removed. It was only much later that it was discovered that the strength of the hydrogen line was connected with the surface temperature of the star. The basic work was done by the "girls" of Harvard College Observatory, primarily Cannon and Antonia Maury, based on the work of Williamina Fleming. These classes are further subdivided by arabic numbers (0-9). A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. The sun is classified as G2.

Spectral types

- Class O stars are very hot and very luminous, being strongly blue in colour. O-stars shines with a power close to a million times solar. These stars have prominent ionized and neutral helium lines and only weak hydrogen lines. Class O stars emit most of their radiation in ultra-violet. :Examples: Zeta Puppis, Epsilon Orionis
- Class B stars are again extremely luminous. Their spectra have neutral helium and moderate hydrogen lines. As O and B stars are so powerful, they live for a very short time. They do not stray far from the area in which they were formed as they don't have the time. They therefore tend to cluster together in what we call OB1 associations, which are associated with giant molecular clouds. The Orion OB1 association is an entire spiral arm of our Galaxy (brighter stars make the spiral arms look brighter, there aren't more stars there) and contains all of the constellation of Orion. :Examples: Rigel, Spica
- Class A stars are amongst the more common naked eye stars. As with all class A stars, they are white. Many white dwarfs are also A. They have strong hydrogen lines and also ionized metals. :Examples: Vega, Sirius
- Class F stars are still quite powerful but they tend to be main sequence stars. Their spectra is characterized by the weaker hydrogen lines and ionized metals, their colour is white with a slight tinge of yellow. :Examples: Canopus, Procyon
- Class G stars are probably the most well known if only for the reason that our Sun is of this class. They have even weaker hydrogen lines than F but along with the ionized metals, they have neutral metals. G is host to the "Yellow Evolutionary Void". Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be. :Examples: Sun, Capella
- Class K are orangish stars which are slightly cooler than our Sun. Some K stars are giants and supergiants, such as Arcturus while others like Alpha Centauri B are main sequence stars. They have extremely weak hydrogen lines, if they are present at all, and mostly neutral metals. :Examples: Arcturus, Aldebaran
- Class M is by far the most common class if we go by the number of stars. All our red dwarfs go in here and they are plentiful; more than 90% of stars are red dwarfs, such as Proxima Centauri. M is also host to most giants and some supergiants such as Antares and Betelgeuse, as well as Mira variables. The spectrum of an M star shows lines belonging to molecules and neutral metals but hydrogen is usually absent. Titanium oxide can be strong in M stars. The red color is deceptive; it is because of the dimness of the star. When an equally hot object, a halogen lamp (3000 K) which is white hot is put at a few kilometers distance, it appears like a red star. :Examples: Betelgeuse, Barnard's star

Spectral types for rare stars

A number of new spectral types have been taken into use for rare types of stars, as they have been discovered:
- W: Up to 70,000 K - Wolf-Rayet stars.
- L: 1,500 - 2,000 K - Stars with masses insufficient to run the regular hydrogen fusion process (brown dwarfs). Class L stars contain lithium which is rapidly destroyed in hotter stars.
- T: 1,000 K - Cooler brown dwarfs with methane in the spectrum.
- C: Carbon stars. :
- R: Formerly a class on its own representing the carbon star equivalent of Class K stars, e.g. S Camelopardalis. :
- N: Formerly a class on its own representing the carbon star equivalent of Class M stars, e.g. R Leporis.
- S: Similar to Class M stars, but with zirconium oxide replacing the regular titanium oxide.
- D: White dwarfs, e.g. Sirius B. Class W represents the superluminous Wolf-Rayet stars, being notably different since they have mostly helium instead of hydrogen. They are thought to be dying supergiants with their hydrogen layer blown away by hot stellar winds caused by their high temperatures, thereby directly exposing their hot helium shell. Class W is subdivided into subclasses WN and WC according to the dominance of nitrogen or carbon in their spectra (and outer layers). Class L stars get their designation from the lithium present in their core. Any lithium would be destroyed in ongoing nuclear reactions in regular stars, which indicates that these objects have no ongoing fusion processes. They are a very dark red in colour and brightest in infrared. Their gas is cool enough to allow metal hydrides and alkali metals to be prominent in the spectrum. Class T stars are very young and low density stars often found in the interstellar clouds they were born in. These are stars barely big enough to be stars and others that are substellar, being of the brown dwarf variety. They are black, emitting little or no visible light but being strongest in infrared. Their surface temperature is a stark contrast to the fifty thousand degrees or more for Class O stars, being merely up to 1,000 K. Complex molecules can form, evidenced by the strong methane lines in their spectra. Class T and L could be more common than all the other classes combined, if recent research is accurate. From studying the number of proplyds (protoplanetary discs, clumps of gas in nebulae from which stars and solar systems are formed) then the number of stars in the galaxy should be several orders of magnitude higher than what we know about. It’s theorised that these proplyds are in a race with each other. The first one to form will become a proto-star, which are very violent objects and will disrupt other propylids in the vicinity, stripping them of their gas. The victim propylids will then probably go on to become main sequence stars or brown dwarf stars of the L and T classes, but quite invisible to us. Since they live so long (no star below 0.8 solar masses has ever died in the history of the galaxy) then these smaller stars will accumulate over time. Class R and N stars are carbon stars (red giants thought to reach the end of their life) which run parallel to the normal classification system from roughly mid G to late M. These have more recently been remapped into a unified carbon classifier C, with N0 starting at roughly C6. Class S stars have ZrO lines rather than TiO, and are in between the Class M stars and the carbon stars. Class S stars have their carbon and oxygen abundances almost exactly equal, and both elements are locked up almost entirely in CO molecules. For stars cool enough for CO to form that molecule tends to "eat up" all of whichever element is less abundant, resulting in "leftover oxygen" on the normal main sequence, "leftover carbon" on the C sequence, and "leftover nothing" on the S sequence. In reality the relation between these stars and the traditional main sequence suggest a rather large continuum of carbon abundance and if fully explored would add another dimension to the stellar classification system. Finally, the classes P and Q are occasionally used for certain non-stellar objects. Type P objects are planetary nebulae and type Q objects are novae.

White dwarf classifications

The class D is sometimes used for white dwarfs, the state most stars end their life in. Class D is further divided into classes DA, DB, DC, DO, DZ, and DQ. Note the letters are not related to the letters used in the classification of true stars, but instead indicate the composition of the white dwarf's outer layer or "atmosphere". The white dwarf classes are as follows:
- DA: a hydrogen-rich "atmosphere" or outer layer, indicated by strong Balmer hydrogen spectral lines.
- DB: a helium-rich "atmosphere" or outer layer, indicated by neutral helium spectral lines.
- DQ: a carbon-rich "atmosphere" or outer layer, indicated by atomic or molecular carbon lines.
- DZ: a 'metal'-rich "atmosphere" or outer layer, indicated by calcium II lines.
- DC: no strong spectral lines indicating one of the above categories.
- DX: spectral lines are insufficiently clear to classify into one of the above categories. All class D stars use the same sequence from 1 to 9, with 1 indicating a temperature above 37,500 K and 9 indicating a temperature below 5,500 K. [http://www.physics.uq.edu.au/people/ross/ph3080/whitey.htm]

Yerkes spectral classification

The Yerkes spectral classification, also called the MKK system from the authors' initials, is a system of stellar spectral classification introduced in 1943 by William Wilson Morgan, Phillip C. Keenan and Edith Kellman of Yerkes Observatory. This classification is based on spectral lines sensitive to stellar surface gravity which is related to luminosity, as opposed to the Harvard classification which is based on surface temperature. Since the radius of a giant star is much larger than a dwarf star while their masses are roughly comparable, the gravity and thus the gas density and pressure on the surface of a giant star are much lower than for a dwarf. These differences manifest themselves in the form of luminosity effects which affect both the width and the intensity of spectral lines which can then be measured. A number of different luminosity classes are distinguished:
- 0 hypergiants (later addition);
- Ia most luminous supergiants;
- Ib less luminous supergiants;
- II bright giants;
- III normal giants;
- IV subgiants;
- V main sequence stars (dwarfs);
- VI subdwarfs (rarely used);
- VII white dwarfs (rarely used) Marginal cases are allowed; for instance a star classified as Ia-0 would be a very luminous supergiant, verging on hypergiant.

UBV system

The UBV system, also called the Johnson system, is a photometric system for classifying stars according to their magnitude. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are measured for a star in order to classify it in the UBV system. The choice of colors on the blue end of the spectrum is because of the bias that photographic film has for those colors. It was introduced in the 1950s by American astronomers Harold Lester Johnson and William Wilson Morgan.

External links

- [http://www.twcac.org/Tutorials/spectral_classes.htm www.twcac.org/Tutorials/spectral_classes.htm]
- [http://www.ucm.es/info/Astrof/invest/actividad/spectra.html Libraries of stellar spectra, D. Montes, UCM] Classification ja:スペクトル分類

Hydrogen

|- | Critical temperature || 32.19 K |- | Critical pressure || 1.315 MPa |- | Critical density || 30.12 g/L (Bohr radius) Hydrogen (Latin: hydrogenium, from Greek: hydro: water, genes: forming) is a chemical element in the periodic table that has the symbol H and atomic number 1. At standard temperature and pressure it is a colorless, odorless, nonmetallic, univalent, highly flammable diatomic gas. Hydrogen is the lightest and most abundant element in the universe. It is present in water, all organic compounds (rare exceptions exist, like buckminsterfullerene) and in all living organisms. Hydrogen is able to react chemically with most other elements. Stars in their main sequence are overwhelmingly composed of hydrogen in its plasma state. The element is used in ammonia production, as a lifting gas, as an alternative fuel, and more recently as a power source of fuel cells. Despite its ubiquity in the universe, hydrogen is surprisingly hard to produce in large quantities on the Earth. In the laboratory, the element is prepared by the reaction of acids on metals such as zinc. The electrolysis of water is a simple method of producing hydrogen, but is economically inefficient for mass production. Large-scale production is usually achieved by steam reforming natural gas. Scientists are now researching new methods for hydrogen production; if they succeed in developing a cost-efficient method of large-scale production, hydrogen may become a viable alternative to greenhouse-gas-producing fossil fuels. One of the methods under investigation involves use of green algae; another promising method involves the conversion of biomass derivatives such as glucose or sorbitol at low temperatures using a catalyst. Yet another method is the "steaming" of Carbon, whereby hydrocarbons are broken down with heat to release hydrogen.

Basic features

Hydrogen is the lightest chemical element; its most common isotope comprises just one negatively charged electron, distributed around a positively charged proton (the nucleus of the atom). The electron is bound to the proton by the Coulomb force, the electrical force that one stationary, electrically charged nanoparticle exerts on another. The hydrogen atom has special significance in quantum mechanics as a simple physical system for which there is an exact solution to the Schrödinger equation; from that equation, the experimentally observed frequencies and intensities of the hydrogen's spectral lines can be calculated. Spectral lines are dark or bright lines in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. At standard temperature and pressure, hydrogen forms a diatomic gas, H₂, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under extreme pressures, such as those at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the extremely low pressure in space—virtually a vacuum—the element tends to exist as individual atoms, simply because there is no way for them to combine. However, clouds of H₂ and singular hydrogen atoms are said to form in H I and H II regions and are associated with star formation, however the existence of singular hydrogen atoms is disputed.. Hydrogen plays a vital role in powering stars through the proton–proton and carbon–nitrogen cycle. These are nuclear fusion processes, which release huge amounts of energy in stars and other hot celestial bodies as hydrogen atoms combine into helium atoms. H₂ is highly soluble in water, alcohol, and ether. It has a high capacity for adsorption, in which it is attached to and held to the surface of some substances. It is an odorless, tasteless, colorless, and highly flammable gas that burns at concentrations as low as 4% H₂ in air. It reacts violently with chlorine and fluorine, forming hydrohalic acids that can damage the lungs and other tissues. When mixed with oxygen, hydrogen explodes on ignition. A unique property of hydrogen is that its flame is completely invisible in air. This makes it difficult to tell if a leak is burning, and carries the added risk that it is easy to walk into a hydrogen fire inadvertently. See also: hydrogen atom.

Applications

Large quantities of hydrogen are needed in the chemical and petrolium industries, notably in the Haber process for the production of ammonia, which by mass ranks as the world's fifth most highly produced industrial compound. Hydrogen is used in the hydrogenation of fats and oils (into items such as margarine), and in the production of methanol. Hydrogen is used in hydrodealkylation, hydrodesulfurization, and hydrocracking. The element has several other important uses.
- The element is used in the manufacture of hydrochloric acid, in welding processes, and in the reduction of metallic ores.
- It is an ingredient in rocket fuels.
- It is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas.
- Liquid hydrogen is used in cryogenic research, including superconductivity studies.
- Since hydrogen is 14.5 times lighter than air, it was once widely used as a lifting agent in balloons and airships. However, this use was curtailed when the Hindenburg disaster convinced the public that the gas was too dangerous for this purpose.
- Deuterium, an isotope of hydrogen (hydrogen-2), is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.
- Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints. There are no "hydrogen wells" or "hydrogen mines" on Earth, so hydrogen cannot be considered a primary energy source like fossil fuels or uranium. Hydrogen can however be burned in internal combustion engines, an approach advocated by BMW's experimental hydrogen car. However, it is currently difficult and dangerous to store and handle in sufficient quantity for motor fuel use. Hydrogen fuel cells are being investigated as mobile power sources with lower emissions than hydrogen-burning internal combustion engines. The low emissions of hydrogen in internal combustion engines and fuel cells are currently offset by the pollution created by hydrogen production. This may change if the substantial amounts of electricity required for water electrolysis can be generated primarily from low pollution sources such as nuclear energy or wind. Research is being conducted on hydrogen as a replacement for fossil fuels. It could become the link between a range of energy sources, carriers and storage. Hydrogen can be converted to and from electricity (solving the electricity storage and transport issues), from bio-fuels, and from and into natural gas and diesel fuel. All of this can theoretically be achieved with zero emissions of CO₂ and toxic pollutants.

History

Hydrogen was first produced by Theophratus Bombastus von Hohenheim (1493–1541)—also known as Paracelsus—by mixing metals with acids. He was unaware that the explosive gas produced by this chemical reaction was hydrogen. In 1671, Robert Boyle described the reaction between two iron fillings and dilute acids, which results in the production of gaseous hydrogen. In 1766, Henry Cavendish was the first to recognize hydrogen as a discrete substance, by identifying the gas from this reaction as "inflammable" and finding that the gas produces water when burned in air. Cavendish stumbled on hydrogen when experimenting with acids and mercury. Although he wrongly assumed that hydrogen was a compound of mercury—and not of the acid—he was still able to accurately describe several key properties of hydrogen. Antoine Lavoisier gave the element its name and proved that water is composed of hydrogen and oxygen. One of the first uses of the element was for balloons. The hydrogen was obtained by mixing sulfuric acid and iron. Harold C. Urey discovered Deuterium, an isotope of hydrogen, by repeated distilling the same sample of water. For this discovery, Urey received the Nobel prize for in 1934. In the same year, the third isotope, tritium, was discovered. Because of its relatively simple structure, hydrogen has often been used in models of how an atom works.

Electron energy levels

The ground state energy level of the electron in a Hydrogen atom is 13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm. With the Bohr Model the energy levels of Hydrogen can be calculated fairly accurately. This is done by modeling the electron as revolving around the proton, much like the earth revolving around the sun. Except the sun holds earth in orbit with the force of gravity, but the proton holds the electron in orbit with the force of electromagnetism. Another difference between the Earth-Sun system and the Electron-Proton system is that, in this model, due to quantum mechanics the electron is allowed to only be at very specific distances from the proton. Modeling the hydrogen atom in this fashion yields the correct energy levels and spectrum.

Occurrence

quantum mechanics.]] Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance in stars and gas giant planets. It is very rare in the Earth's atmosphere (1 ppm by volume), because being the lightest gas causes it to escape Earth's gravity, though when compounds are considered, it is the tenth most abundant element on Earth. The most common source for this element on Earth is water, which is composed two parts hydrogen to one part oxygen (H₂O). Other sources include most forms of organic matter (currently all known life forms) including coal, natural gas, and other fossil fuels. Methane (CH₄) is an increasingly important source of hydrogen. Throughout the Universe, hydrogen is mostly found in the plasma state whose properties are quite different to molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity, even when the gas is only partially ionised. The charged particles are highly influenced by magnetic and electric fields, for example, in the Solar Wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen can be prepared in several different ways: steam on heated carbon, hydrocarbon decomposition with heat, reaction of a strong base in an aqueous solution with aluminium, water electrolysis, or displacement from acids with certain metals. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (700–1100 °C), steam reacts with methane to yield carbon monoxide and hydrogen. :CH₄ + H₂O → CO + 3 H₂ Additional hydrogen can be recovered from the carbon monoxide through the water-gas shift reaction: :CO + H₂O → CO₂ + H₂

Compounds

The lightest of all gases, hydrogen combines with most other elements to form compounds. Hydrogen has an electronegativity of 2.2, so it forms compounds where it is the more nonmetallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H^- ions or just as a solute within the other element (as in palladium hydride). The latter tend to be covalent, since the H⁺ ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. These both form acids. Thus even in an acidic solution one sees ions like hydronium (H₃O⁺) as the protons latch on to something. Although exotic on earth, one of the most common ions in the universe is the H₃⁺ ion. Hydrogen combines with oxygen to form water, H₂O, and releases a lot of energy in doing so, burning explosively in air. Deuterium oxide, or D₂O, is commonly referred to as heavy water. Hydrogen also forms a vast array of compounds with carbon. Because of their association with living things, these compounds are called organic compounds, and the study of the properties of these compounds is called organic chemistry. organic chemistry

Forms

Under normal conditions, hydrogen gas is a mix of two different kinds of molecules which differ from one another by the relative spin of the nuclei. These two forms are known as ortho- and para-hydrogen (this is different from isotopes, see below). In ortho-hydrogen the nuclear spins are parallel (form a triplet), while in para they are antiparallel (form a singlet). At standard conditions hydrogen is composed of about 25% of the para form and 75% of the ortho form (the so-called "normal" form). The equilibrium ratio of these two forms depends on temperature, but since the ortho form has higher energy (is an excited state), it cannot be stable in its pure form. In low temperatures (around boiling point), the equilibrium state is comprised almost entirely of the para form. The conversion process between the forms is slow, and if hydrogen is cooled down and condensed rapidly, it contains large quantities of the ortho form. It is important in preparation and storage of liquid hydrogen, since the ortho-para conversion produces more heat than the heat of its evaporation, and a lot of hydrogen can be lost by evaporation in this way during several days after liquefying. Therefore, some catalysts of the ortho-para conversion process are used during hydrogen cooling. The two forms have also slightly different physical properties. For example, the melting and boiling points of parahydrogen are about 0.1 K lower than of the "normal" form.

Isotopes

Hydrogen is the only element that has different names for its isotopes. (During the early study of radioactivity, various heavy radioactive isotopes were given names, but such names are no longer used, although one element, radon, has a name that originally applied to only one of its isotopes.) The symbols D and T (instead of ²H and ³H) are sometimes used for deuterium and tritium, although this is not officially sanctioned. (The symbol P is already in use for phosphorus and is not available for protium.) ;¹H The most common isotope of hydrogen, this stable isotope has a nucleus consisting of a single proton; hence the descriptive, although rarely used, name protium. The spin of a protium atom is 1/2+. ;²H The other stable isotope is deuterium, with an extra neutron in the nucleus. Deuterium comprises 0.0184%–0.0082% of all hydrogen (IUPAC); ratios of deuterium to protium are reported relative to the VSMOW standard reference water. The spin of a deuterium atom is 1+. ;³H The third naturally occurring hydrogen isotope is the radioactive tritium. The tritium nucleus contains two neutrons in addition to the proton. It decays through beta decay and has a half-life of 12.32 years. Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. Like ordinary hydrogen, tritium reacts with the oxygen in the atmosphere to form T₂O. This radioactive "water" molecule constantly enters the Earth's seas and lakes in the form of slightly radioactive rain, but its half-life is short enough to prevent a buildup of hazardous radioactivity. The spin of a tritium atom is 1/2+. ;⁴H Hydrogen-4 was synthesized by bombarding tritium with fast-moving deuterium nuclei. It decays through neutron emission and has a half-life of 9.93696x10^-23 seconds. The spin of a hydrogen-4 atom is 2-. ;⁵H In 2001 scientists detected hydrogen-5 by bombarding a hydrogen target with heavy ions. It decays through neutron emission and has a half-life of 8.01930x10^-23 seconds. ;⁶H Hydrogen-6 decays through triple neutron emission and has a half-life of 3.26500^-22 seconds. ;⁷H In 2003 hydrogen-7 was created ([http://physicsweb.org/articles/news/7/3/3 article]) at the RIKEN laboratory in Japan by colliding a high-energy beam of helium-8 atoms with a cryogenic hydrogen target and detecting tritons—the nuclei of tritium atoms—and neutrons from the breakup of hydrogen-7, the same method used to produce and detect hydrogen-5.

References

# # # # # #
- [http://www.riken.go.jp/engn/r-world/research/lab/wako/ribeam/ RIKEN Beam Science Laboratory, Japan - Heavy hydrogen research]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes] Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989 ;Book references:
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External links

- [http://www.hydropole.ch/Hydropole/Intro/Phasediag.gif Hydrogen phase diagram.]
- [http://www.compchemwiki.org/index.php?title=Hydrogen Computational Chemistry Wiki] Category:Nonmetals Category:Fuels Category:Chemical elements ko:수소 ms:Hidrogen ja:水素 simple:Hydrogen th:ไฮโดรเจน

Binary star

:This article is about a star system. For the rap group, see Binary Star (rap). A binary star system consists of two stars both orbiting around their barycenter. For each star, the other is its "companion star". The term "binary star" was apparently first coined by Sir William Herschel in 1802 to designate "a real double star — the union of two stars that are formed together in one system by the laws of attraction". Any two stars seen close to one another form a double star, the most famous being Mizar and Alcor in the Big Dipper. Odds are, though, that a double star is probably a foreground and background star pair that only looks like a binary system —the two stars are, in reality, widely separated in space but just happen to lie in roughly the same direction as seen from our vantage point. Such "false binaries" are termed optical binaries. With the invention of the telescope, many such pairs were found. Herschel, in 1780, measured the separation and orientations of over 700 pairs that appeared to be binary systems and found that about 50 pairs changed orientation over two decades of observation. A binary star is thus a pair of stars that are held together by the force of gravity. Systems in which the individual stars that compose a binary star can be resolved (distinguished) with a powerful enough telescope (including by interferometric methods) are known as visual binaries. In other cases, the only indication of binarity is obtained from the Doppler shift of the spectral lines. These systems, known as spectroscopic binaries, consist of relatively close pairs of stars whose orbital plane is substantially inclined with respect to the plane of the celestial sphere, such that the spectral lines of both stars are seen to shift regularly to the blue and then to the red, as they orbit towards and away from us. If the orbital plane is very nearly perpendicular to the plane of the celestial sphere, such that the two stars actually occult each other regularly, one has an eclipsing binary. Binary stars that are simultaneously visual and spectroscopic binaries are rare, and they are a precious source of valuable information when found. Visual binary stars, unless they are relatively close to Earth, have a large true separation, and consequently their orbital speeds are usually too small to be measured spectroscopically. Conversely, spectroscopic binary stars move fast in their orbits, and this is because they are close together — usually too close to be detected as visual binaries. Binaries that are both visual and spectroscopic are thus usually relatively close to us. Scientists have discovered some stars that seem to orbit around an empty space. Astrometric binaries, for example, are relatively nearby stars which can be seen to wobble around a middle point, with no visible companion. With some spectroscopic binaries, there is only one set of lines shifting back and forth. The same arguments for ordinary binaries can be used to infer the mass of the missing companion. The companion could be very dim, such that it is currently undetectable or lost in the glare of its primary, or it could be an object that doesn't shine in visible light, like a neutron star. In some instances, one can make a very strong case that the missing companion is in fact a black hole —a star with such strong gravitational force that no light is able to get out. Perhaps the best example of such a system is Cygnus X-1, where the mass of the unseen companion is about nine times the mass of our sun —far exceeding the maximum mass of a neutron star, the other likely candidate for the companion. Binaries are particularly crucial as one of the primary methods by which astronomers can directly measure the mass of a distant star. The gravitational pull between the individual stars of a binary causes each to orbit around the other. From the orbital pattern of a visual binary, or the time variation of the spectrum of a spectroscopic binary, the mass of its stars can therefore be determined. Because a majority of stars exist in binary systems, binaries are particularly important to our understanding of the processes by which stars form. In particular, the period and masses of the binary tell us about the amount of angular momentum in the system. Because angular momentum is a conserved quantity in physics, binaries give us important clues about the conditions in which the stars were themselves formed.

Binary star classifications

At present, binary stars are classified into four types according to their observable properties:
- visual binaries
- spectroscopic binaries
- eclipsing binaries
- astrometric binaries Any star can belong to several of these classes, e.g., several spectroscopic binaries are also eclipsing binaries. Another three-category classification is based on the distance of the stars, relative to their sizes :
- detached binaries
- semi-detached binaries
- contact binaries

Research findings

During the past 200 years a large amount of research has been carried out on binary stars leading to some general conclusions. It is believed that at least a quarter of all stars are at least binary systems, with as many as 10% of these systems containing more than two stars (ternary etc.). There is a direct correlation between the period of revolution of a binary star and the eccentricity of its orbit, with systems of short period having smaller eccentricity. Binary stars may be found with any conceivable separation, from pairs orbiting so closely that they are practically in contact with each other, to pairs so distantly separated that their connection is indicated only by their common proper motion through space. Remarkably, among gravitationally-bound binary star sytems, there exists a log normal distribution of periods, with the majority of these systems orbiting with a period of about 100 years. In pairs where the two stars are of equal brightness, they are also of the same spectral type. In systems where the brightnesses are different, the fainter star is bluer if the brighter star is a giant star and redder if the brighter star belongs to the main sequence. Since mass can be determined only from gravitational attraction, and the only stars (with the exception of the Sun, and gravitationally-lensed stars) for which the gravitational attraction can be determined are binary stars, binaries constitute a uniquely important class of stars. In the case of a visual binary star, after the orbit has been determined and the stellar parallax of the system obtained, the combined mass of the two stars may be obtained by a direct application of the Keplerian harmonic law. Unfortunately, it is impossible to obtain the complete orbit of a spectroscopic binary unless it is also a visual or an eclipsing binary, so from these objects only a determination of the joint product of mass and the sine of the angle of inclination relative to the line of sight is possible. Therefore, without additional information regarding the angle of inclination, the mass can only be inferred in a statistical sense. In the case of eclipsing binaries which are also spectroscopic binaries it is possible to make a complete solution for the specifications (mass, density, size, luminosity, and approximate shape) of both members of the system. Science Fiction has often featured planets of binary or ternary stars as a setting. In reality, some orbital ranges are impossible for dynamical reasons (the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range), whilst other orbits present serious challenges for eventual biospheres because of possible extreme variations in surface temperature over time. Detecting planets around multiple star systems introduces all sorts of additional technical difficulties, which may be why so far (July 2005) only one such planet has been found: HD 188753 Ab.

Binary star examples

- Albireo
- Algol (triple, eclipsing binary)
- Alpha Centauri (triple)
- Castor (sextuple)
- Procyon
- Sirius

External links

- [http://en.wikibooks.org/wiki/GAT:_binary_star Wikibooks: Glossary of Astronomical Terms (GAT): Binary star] Category:Star types Category:Star systems ko:쌍성 ja:連星

Metal-poor

Metal-poor is a term that is used to describe the chemical make up of an object. Typically the chemicals which are most often referenced in astronomy are hydrogen and helium, with all others being referred to as metals. In astronomy circles, a "metal" refers to any element heavier than helium. Metals make up only a small percentage of the chemical make up of the universe, even 13.7 billion years after the Big Bang. Shortly after the Big Bang, the universe was comprised entirely of hydrogen, helium, and trace amounts of deuterium and lithium. These elements were created during the era of nucleosynthesis, (which lasted from .0001 - 3s after the Big Bang.) These primitive atomic structures made up the primordial material from which the first stars were born. Metal-poor objects are those which contain relatively small amounts of the elements heavier than helium. The idea of a "relatively" small amount must be kept in mind because even metal-rich objects contain very small amounts of any element other than hydrogen; however, metal-poor objects are even more primitive. These objects formed during earlier times in the universe. The first stars, referred to as Population III, were incredibly massive and, during their lives, they created the elements up to iron in a process known as nucleosynthesis. These large stars had spectacular deaths through supernovae and created all the elements heavier than iron. This "polluted" the universe with metals. The next generation of stars were born out of these materials left by the supernova outbursts. Thus, the most metal-poor objects were born the earliest. As subsequent generations of stars were born, they became more metal-enriched, as the gaseous clouds from which they formed because more metal-rich. The next generation of stars are known as Population II and are the earliest stars which have been directly observed. In the past couple years, a team of scientists have been targetting these oldest stars in the Hamburg-ESO survey. Thus far, they have uncovered two of the oldest stars known to date: HE0107-5240 and HE1327- 2326. Despite their incredibly low metal content, these stars are still a part of Population II. Stars which are metal-poor are classified as such because they have a low metallicity. Metallicity is a measure of the amount of hydrogen to other elements. Iron is a very common element used to determine the metallicity of a star. Standard nomenclature often uses [Fe/H] which is a logarithmic ratio of the iron to hydrogen in a star compared with the iron to hyrdogen ratio of the Sun. Stars of a metallicity below -6 are considered Population III. Thus far, none have been found.

References

# # Category:Population II stars Category:Stars by metallicity

Subdwarf

A subdwarf star, sometimes denoted by "sd", is luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type; this is due to subdwarfs having lower metallicity than other main sequence stars. On an Hertzsprung-Russell diagram subdwarfs appear to lie below the main sequence. Subdwarfs are mostly Population II stars. The term "subdwarf" was coined by Gerard Peter Kuiper in 1939, to refer to a series of stars with anomalous spectra that were previously labeled as "intermediate white dwarfs."(1) Often being members of the Milky Way's halo, they frequently have high space velocities relative to the Sun. They also emit a higher percentage of ultraviolet light for the same spectral type relative to a Population I star; this ultraviolet excess is a result of their low metallicity, which allows more of their ultraviolet light to escape.(2) Thus, the relatively low opacity of their outer layers lowers the