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114-555: The word "Hipparcos" is an acronym for HIgh Precision PARallax COllecting Satellite and also a reference to the ancient Greek astronomer Hipparchus of Nicaea, who is noted for applications of trigonometry to astronomy and his discovery of the precession of the equinoxes . By the second half of the 20th century, the accurate measurement of star positions from the ground was running into essentially insurmountable barriers to improvements in accuracy, especially for large-angle measurements and systematic terms. Problems were dominated by

228-428: A numeronym . For example, "i18n" abbreviates " internationalization ", a computer-science term for adapting software for worldwide use; the "18" represents the 18 letters that come between the first and the last in "internationalization". Similarly, "localization" can be abbreviated "l10n"; " multilingualization " "m17n"; and " accessibility " "a11y". In addition to the use of a specific number replacing that many letters,

342-645: A single word ("television" or "transvestite", for instance), and is in general spelled without punctuation (except in the plural). Although "PS" stands for the single English word " postscript " or the Latin postscriptum , it is often spelled with periods ("P.S.") as if parsed as Latin post scriptum instead. The slash ('/', or solidus ) is sometimes used to separate the letters in an acronym, as in "N/A" ("not applicable, not available") and "c/o" ("care of"). Inconveniently long words used frequently in related contexts can be represented according to their letter count as

456-507: A 1940 translation of a novel by the German writer Lion Feuchtwanger . It is an unsettled question in English lexicography and style guides whether it is legitimate to use the word acronym to describe forms that use initials but are not pronounced as a word. While there is plenty of evidence that acronym is used widely in this way, some sources do not acknowledge this usage, reserving

570-435: A 7-parameter, or even 9-parameter model fit (compared to the standard 5-parameter model), and typically such models could be enhanced in complexity until suitable fits were obtained. A complete orbit, requiring 7 elements, was determined for 45 systems. Orbital periods close to one year can become degenerate with the parallax, resulting in unreliable solutions for both. Triple or higher-order systems provided further challenges to

684-452: A comprehensive system of cross-checking and validation, and is described in detail in the published catalogue. A detailed optical calibration model was included to map the transformation from sky to instrumental coordinates. Its adequacy could be verified by the detailed measurement residuals. The Earth's orbit, and the satellite's orbit with respect to the Earth , were essential for describing

798-625: A different meaning. Medical literature has been struggling to control the proliferation of acronyms, including efforts by the American Academy of Dermatology. Acronyms are often taught as mnemonic devices: for example the colors of the rainbow are ROY G. BIV (red, orange, yellow, green, blue, indigo, violet). They are also used as mental checklists: in aviation GUMPS stands for gas-undercarriage-mixture-propeller-seat belts. Other mnemonic acronyms include CAN SLIM in finance, PAVPANIC in English grammar, and PEMDAS in mathematics. It

912-517: A five-digit star number within each region, separated by a decimal point. sty2 lists Tycho-2 stars by number or sky region. imty2 lists the Tycho-2 stars within an IRAF or FITS image using the world coordinate system defined in its header. A Perl program for extracting data from the catalogue is available from http://archive.eso.org/ASTROM/ . Tycho-2 File Formats WCSTools software uses the files catalog.dat and index.dat. The following FTP sites make

1026-413: A long orbital period such that non-linear motions of the photocentre were insignificant over the short (3-year) measurement duration, the binary nature of the star would pass unrecognised by Hipparcos , but could show as a Hipparcos proper motion discrepant compared to those established from long temporal baseline proper motion programmes on ground. Higher-order photocentric motions could be represented by

1140-732: A mean number of 110 observations per star, and a median photometric precision (Hp<9 magnitude) of 0.0015 magnitude, with 11,597 entries were identified as variable or possibly-variable. For the star mapper results, the data analysis was carried out by the Tycho Data Analysis Consortium (TDAC). The Tycho Catalogue comprises more than one million stars with 20–30 milliarc-sec astrometry and two-colour (B and V band) photometry. The final Hipparcos and Tycho Catalogues were completed in August 1996. The catalogues were published by European Space Agency (ESA) on behalf of

1254-781: A medial decimal point . Particularly in British and Commonwealth English , all such punctuation marking acronyms and other capitalized abbreviations is now uncommon and considered either unnecessary or incorrect. The presence of all-capital letters is now thought sufficient to indicate the nature of the UK , the EU , and the UN . Forms such as the U.S.A. for "the United States of America " are now considered to indicate American or North American English . Even within those dialects, such punctuation

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1368-414: A more secure empirical basis. Observationally, the objective was to provide the positions, parallaxes , and annual proper motions for some 100,000 stars with an unprecedented accuracy of 0.002  arcseconds , a target in practice eventually surpassed by a factor of two. The name of the space telescope, "Hipparcos", was an acronym for High Precision Parallax Collecting Satellite , and it also reflected

1482-522: A multinational context. Its acceptance within the European Space Agency 's scientific programme, in 1980, was the result of a lengthy process of study and lobbying . The underlying scientific motivation was to determine the physical properties of the stars through the measurement of their distances and space motions, and thus to place theoretical studies of stellar structure and evolution, and studies of galactic structure and kinematics, on

1596-407: A period when the letters are pronounced individually, as in " K.G.B. ", but not when pronounced as a word, as in " NATO ". The logic of this style is that the pronunciation is reflected graphically by the punctuation scheme. When a multiple-letter abbreviation is formed from a single word, periods are in general not used, although they may be common in informal usage. "TV", for example, may stand for

1710-420: A sensitive field of view of about 38-arc-sec diameter converted the modulated light into a sequence of photon counts (with a sampling frequency of 1200 Hz ) from which the phase of the entire pulse train from a star could be derived. The apparent angle between two stars in the combined fields of view, modulo the grid period, was obtained from the phase difference of the two star pulse trains. Originally targeting

1824-436: A single word, such as NATO (as distinct from B-B-C )" but adds later "In everyday use, acronym is often applied to abbreviations that are technically initialisms, since they are pronounced as separate letters." The Chicago Manual of Style acknowledges the complexity ("Furthermore, an acronym and initialism are occasionally combined (JPEG), and the line between initialism and acronym is not always clear") but still defines

1938-515: A twentieth-century phenomenon. Linguist David Wilton in Word Myths: Debunking Linguistic Urban Legends claims that "forming words from acronyms is a distinctly twentieth- (and now twenty-first-) century phenomenon. There is only one known pre-twentieth-century [English] word with an acronymic origin and it was in vogue for only a short time in 1886. The word is colinderies or colinda , an acronym for

2052-471: A word, an abbreviation is not an acronym." In contrast, some style guides do support it, whether explicitly or implicitly. The 1994 edition of Merriam-Webster's Dictionary of English Usage defends the usage on the basis of a claim that dictionaries do not make a distinction. The BuzzFeed style guide describes CBS and PBS as "acronyms ending in S". Acronymy, like retronymy , is a linguistic process that has existed throughout history but for which there

2166-677: A word. American English dictionaries such as Merriam-Webster , Dictionary.com's Random House Webster's Unabridged Dictionary and the American Heritage Dictionary as well as the British Oxford English Dictionary and the Australian Macquarie Dictionary all include a sense in their entries for acronym equating it with initialism , although The American Heritage Dictionary criticizes it with

2280-572: Is a subset with a narrower definition: an initialism pronounced as a word rather than as a sequence of letters. In this sense, NASA / ˈ n æ s ə / is an acronym but USA / j uː ɛ s ˈ eɪ / is not. The broader sense of acronym , ignoring pronunciation, is its original meaning and in common use. Dictionary and style-guide editors dispute whether the term acronym can be legitimately applied to abbreviations which are not pronounced as words, and they do not agree on acronym spacing , casing , and punctuation . The phrase that

2394-417: Is a function of time. The resulting effect of secular or perspective acceleration is the interpretation of a transverse acceleration actually arising from a purely linear space velocity with a significant radial component, with the positional effect proportional to the product of the parallax, the proper motion, and the radial velocity. At the accuracy levels of Hipparcos it is of (marginal) importance only for

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2508-488: Is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, Kate L. Turabian 's A Manual for Writers of Research Papers, Theses, and Dissertations , writing about style in academic writings, allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" but "Ph.D.'s". The style guides of

2622-721: Is becoming increasingly uncommon. Some style guides , such as that of the BBC , no longer require punctuation to show ellipsis ; some even proscribe it. Larry Trask , American author of The Penguin Guide to Punctuation , states categorically that, in British English , "this tiresome and unnecessary practice is now obsolete." Nevertheless, some influential style guides , many of them American , still require periods in certain instances. For example, The New York Times Manual of Style and Usage recommends following each segment with

2736-411: Is common for grammatical contractions (e.g. don't , y'all , and ain't ) and for contractions marking unusual pronunciations (e.g. a'ight , cap'n , and fo'c'sle for "all right", "captain", and "forecastle"). By the early twentieth century, it was standard to use a full stop/period/point , especially in the cases of initialisms and acronyms. Previously, especially for Latin abbreviations , this

2850-631: Is especially important for paper media, where no search utility is available to find the first use.) It also gives students a convenient review list to memorize the important acronyms introduced in a textbook chapter. Expansion at first use and abbreviation keys originated in the print era, but they are equally useful for electronic text . While acronyms provide convenience and succinctness for specialists, they often degenerate into confusing jargon . This may be intentional, to exclude readers without domain-specific knowledge. New acronyms may also confuse when they coincide with an already existing acronym having

2964-467: Is generally imperceptible to astrometric measurements (in the plane of the sky), and therefore it is generally ignored in large-scale astrometric surveys. In practice, it can be measured as a Doppler shift of the spectral lines. More strictly, however, the radial velocity does enter a rigorous astrometric formulation. Specifically, a space velocity along the line-of-sight means that the transformation from tangential linear velocity to (angular) proper motion

3078-464: Is generally said as two letters, but IPsec for Internet Protocol Security is usually pronounced as / ˌ aɪ ˈ p iː s ɛ k / or / ˈ ɪ p s ɛ k / , along with variant capitalization like "IPSEC" and "Ipsec". Pronunciation may even vary within a single speaker's vocabulary, depending on narrow contexts. As an example, the database programming language SQL is usually said as three letters, but in reference to Microsoft's implementation

3192-459: Is not uncommon for acronyms to be cited in a kind of false etymology , called a folk etymology , for a word. Such etymologies persist in popular culture but have no factual basis in historical linguistics , and are examples of language-related urban legends . For example, " cop " is commonly cited as being derived, it is presumed, from "constable on patrol", and " posh " from " port outward, starboard home ". With some of these specious expansions,

3306-475: Is sometimes used to study other long-period exoplanets , such as HR 5183 b . Acronym An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial letter of each word in all caps with no punctuation . For some, an initialism or alphabetism , connotes this general meaning, and an acronym

3420-526: Is the Galactic latitude). Stars constituting this survey are flagged in the Hipparcos Catalogue . The second component comprised additional stars selected according to their scientific interest, with none fainter than about magnitude V=13 mag. These were selected from around 200 scientific proposals submitted on the basis of an Invitation for Proposals issued by ESA in 1982, and prioritised by

3534-415: Is traditionally pronounced like the word sequel . In writing for a broad audience, the words of an acronym are typically written out in full at its first occurrence within a given text. Expansion At First Use (EAFU) benefits readers unfamiliar with the acronym. Another text aid is an abbreviation key which lists and expands all acronyms used, a reference for readers who skipped past the first use. (This

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3648-483: The Centre de données astronomiques de Strasbourg . The Hipparcos results have affected a very broad range of astronomical research, which can be classified into three major themes: Associated with these major themes, Hipparcos has provided results in topics as diverse as Solar System science, including mass determinations of asteroids, Earth's rotation and Chandler wobble ; the internal structure of white dwarfs ;

3762-516: The Colonial and Indian Exposition held in London in that year." However, although acronymic words seem not to have been employed in general vocabulary before the twentieth century (as Wilton points out), the concept of their formation is treated as effortlessly understood (and evidently not novel) in an Edgar Allan Poe story of the 1830s, " How to Write a Blackwood Article ", which includes

3876-536: The Hipparcos and Tycho catalogues. A detailed review of the Hipparcos scientific literature between 1997 and 2007 was published in 2009, and a popular account of the project in 2010. Some examples of notable results include (listed chronologically): One controversial result has been the derived proximity, at about 120 parsecs, of the Pleiades cluster, established both from the original catalogue as well as from

3990-705: The Hipparcos Input Catalogue (HIC): each star in the final Hipparcos Catalogue was contained in the Input Catalogue. The Input Catalogue was compiled by the INCA Consortium over the period 1982–1989, finalised pre-launch, and published both digitally and in printed form. Although fully superseded by the satellite results, it nevertheless includes supplemental information on multiple system components as well as compilations of radial velocities and spectral types which, not observed by

4104-502: The Hubble Space Telescope ; photographic programmes to determine stellar proper motions with respect to extragalactic objects (Bonn, Kiev, Lick, Potsdam, Yale/San Juan); and comparison of Earth rotation parameters obtained by Very-long-baseline interferometry (VLBI) and by ground-based optical observations of Hipparcos stars. Although very different in terms of instruments, observational methods and objects involved,

4218-551: The Millennium Star Atlas : an all-sky atlas of one million stars to visual magnitude 11. Some 10,000 nonstellar objects are also included to complement the catalogue data. Between 1997 and 2007, investigations into subtle effects in the satellite attitude and instrument calibration continued. A number of effects in the data that had not been fully accounted for were studied, such as scan-phase discontinuities and micrometeoroid-induced attitude jumps. A re-reduction of

4332-623: The Modern Language Association and American Psychological Association prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas The New York Times Manual of Style and Usage requires an apostrophe when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's"). Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, "the C.D.'s' labels" (the labels of

4446-498: The PPN formalism . Residuals were examined to establish limits on any deviations from this general relativistic value, and no significant discrepancies were found. The satellite observations essentially yielded highly accurate relative positions of stars with respect to each other, throughout the measurement period (1989–1993). In the absence of direct observations of extragalactic sources (apart from marginal observations of quasar 3C 273 )

4560-539: The Restoration witticism arranging the names of some members of Charles II 's Committee for Foreign Affairs to produce the "CABAL" ministry . OK , a term of disputed origin, dates back at least to the early nineteenth century and is now used around the world. Acronyms are used most often to abbreviate names of organizations and long or frequently referenced terms. The armed forces and government agencies frequently employ acronyms; some well-known examples from

4674-697: The Tycho-1 Catalogue (ESA SP-1200, 1997). However, Tycho-2 is much larger and a bit more precise, because a more advanced reduction technique was used. The U.S. Naval Observatory (USNO) first compiled the ACT Reference Catalog, (Astrographic Catalogue / Tycho) containing nearly one million stars, by combining the Astrographic Catalogue (AC 2000) with the Tycho-1 Catalogue; the large epoch span between

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4788-480: The "belief" that the etymology is acronymic has clearly been tongue-in-cheek among many citers, as with "gentlemen only, ladies forbidden" for " golf ", although many other (more credulous ) people have uncritically taken it for fact. Taboo words in particular commonly have such false etymologies: " shit " from "ship/store high in transit" or "special high-intensity training" and " fuck " from "for unlawful carnal knowledge", or "fornication under consent/command of

4902-463: The 160-character SMS limit, and to save time, acronyms such as "GF" ("girlfriend"), "LOL" ("laughing out loud"), and "DL" ("download" or "down low") have become popular. Some prescriptivists disdain texting acronyms and abbreviations as decreasing clarity, or as failure to use "pure" or "proper" English. Others point out that languages have always continually changed , and argue that acronyms should be embraced as inevitable, or as innovation that adapts

5016-461: The 18 letters between the initial "i" and the final "n"). Authors of expository writing will sometimes capitalize or otherwise distinctively format the initials of the expansion for pedagogical emphasis (for example, writing: "the onset of Congestive Heart Failure (CHF)" or "the onset of c ongestive h eart f ailure (CHF)"). Capitalization like this, however, conflicts with the convention of English orthography, which generally reserves capitals in

5130-466: The British press may render it "Nato"), but uses lower case in " Unicef " (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals"). While abbreviations typically exclude the initials of short function words (such as "and", "or", "of", or "to"), this is not always

5244-769: The Scientific Proposal Selection Committee in consultation with the Input Catalogue Consortium. This selection had to balance 'a priori' scientific interest, and the observing programme's limiting magnitude, total observing time, and sky uniformity constraints. For the main mission results, the data analysis was carried out by two independent scientific teams, NDAC and FAST, together comprising some 100 astronomers and scientists, mostly from European (ESA-member state) institutes. The analyses, proceeding from nearly 1000 Gbit of satellite data acquired over 3.5 years, incorporated

5358-568: The Tycho (and Tycho-2) Catalogue, provided two colours, roughly B and V in the Johnson UBV photometric system , important for spectral classification and effective temperature determination. Classical astrometry concerns only motions in the plane of the sky and ignores the star's radial velocity , i.e. its space motion along the line-of-sight. Whilst critical for an understanding of stellar kinematics, and hence population dynamics, its effect

5472-455: The Tycho-2 catalogue available as 20 gzipped files. After retrieving them and the index.dat file, combine the gzipped files into catalog.dat. The resulting files will differ from the files on the CD-ROM in that they will end lines with only a linefeed, while the CD-ROM version for which WCSTools software was written terminates lines with a carriage return and a linefeed. Add the carriage returns to

5586-564: The U.S. Navy, is "COMCRUDESPAC", which stands for "commander, cruisers destroyers Pacific"; it is also seen as "ComCruDesPac". Inventors are encouraged to anticipate the formation of acronyms by making new terms "YABA-compatible" ("yet another bloody acronym"), meaning the term's acronym can be pronounced and is not an offensive word: "When choosing a new name, be sure it is 'YABA-compatible'." Acronym use has been further popularized by text messaging on mobile phones with short message service (SMS), and instant messenger (IM). To fit messages into

5700-560: The United States are among the " alphabet agencies " (jokingly referred to as " alphabet soup ") created under the New Deal by Franklin D. Roosevelt (himself known as "FDR"). Business and industry also coin acronyms prolifically. The rapid advance of science and technology also drives the usage, as new inventions and concepts with multiword names create a demand for shorter, more pronounceable names. One representative example, from

5814-411: The acronym may use normal case rules, e.g. it would appear generally in lower case, but with an initial capital when starting a sentence or when in a title. Once knowledge of the words underlying such an acronym has faded from common recall, the acronym may be termed an anacronym . Examples of anacronyms are the words " scuba ", " radar ", and " laser ". The word "an acro nym" should not be confused with

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5928-545: The acronym stands for is called its expansion . The meaning of an acronym includes both its expansion and the meaning of its expansion. The word acronym is formed from the Greek roots akro- , meaning 'height, summit, or tip', and -nym , 'name'. This neoclassical compound appears to have originated in German , with attestations for the German form Akronym appearing as early as 1921. Citations in English date to

6042-590: The adoption of acronyms was modern warfare, with its many highly technical terms. While there is no recorded use of military acronyms dating from the American Civil War (acronyms such as "ANV" for " Army of Northern Virginia " post-date the war itself), they became somewhat common in World War I , and by World War II they were widespread even in the slang of soldiers, who referred to themselves as G.I.s . The widespread, frequent use of acronyms across

6156-506: The apostrophe should be reserved for the possessive ("the TV's antenna"). In some languages, the convention of doubling the letters in the acronym is used to indicate plural words: for example, the Spanish EE.UU. , for Estados Unidos ('United States'). This old convention is still sometimes followed for a limited number of English abbreviations, such as SS. for Saints , pp. for

6270-427: The associated steps of the analysis was eventually undertaken. This has led to improved astrometric accuracies for stars brighter than Hp=9.0 magnitude, reaching a factor of about three for the brightest stars (Hp<4.5 magnitude), while also underlining the conclusion that the Hipparcos Catalogue as originally published is generally reliable within the quoted accuracies. All catalogue data are available online from

6384-462: The astrometric error is 7 milliarcseconds. The overall error for all stars is 60 milliarcseconds. The observational period was from 1989.85 to 1993.21 and the mean satellite observation epoch is 1991.5. Photometric accuracy for stars brighter than Vt=9 is 0.013 magnitude; for all stars it is 0.10 magnitude. To enable rapid access of specific stars in the catalogue, WCSTools software numbers each star using its Guide Star region number (0001 to 9537) and

6498-477: The brightest stars in the Milky Way. Components of double stars with separations down to 0.8 arcseconds are included. The catalogue is 99% complete to magnitudes of V~11.0 and 90% complete to V~11.5. (, Table 1) The Tycho-2 positions and magnitudes are based on the observations collected by the star mapper of the European Space Agency 's Hipparcos satellite. They are the same observations used to compile

6612-1163: The case. Sometimes function words are included to make a pronounceable acronym, such as CORE ( Congress of Racial Equality ). Sometimes the letters representing these words are written in lower case, such as in the cases of "TfL" (" Transport for London ") and LotR ( The Lord of the Rings ); this usually occurs when the acronym represents a multi-word proper noun. Numbers (both cardinal and ordinal ) in names are often represented by digits rather than initial letters, as in "4GL" (" fourth generation language ") or "G77" (" Group of 77 "). Large numbers may use metric prefixes , as with " Y2K " for "Year 2000". Exceptions using initials for numbers include " TLA " ("three-letter acronym/abbreviation") and "GoF" (" Gang of Four "). Abbreviations using numbers for other purposes include repetitions, such as " A2DP " ("Advanced Audio Distribution Profile"), " W3C " ("World Wide Web Consortium"), and T3 ( Trends, Tips & Tools for Everyday Living ); pronunciation, such as " B2B " ("business to business"); and numeronyms , such as "i18n" ("internationalization"; "18" represents

6726-473: The common focal plane. This complex mirror consisted of two mirrors tilted in opposite directions, each occupying half of the rectangular entrance pupil, and providing an unvignetted field of view of about 1° × 1°. The telescope used a system of grids, at the focal surface, composed of 2688 alternate opaque and transparent bands, with a period of 1.208 arc-sec (8.2 micrometre). Behind this grid system, an image dissector tube ( photomultiplier type detector) with

6840-413: The compact discs). In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is "S", as in "SOS's" (although abbreviations ending with S can also take "-es", e.g. "SOSes"), or when pluralizing an abbreviation that has periods. A particularly rich source of options arises when the plural of an acronym would normally be indicated in a word other than

6954-564: The contrived acronym "P.R.E.T.T.Y.B.L.U.E.B.A.T.C.H." The use of Latin and Neo-Latin terms in vernaculars has been pan-European and pre-dates modern English. Some examples of acronyms in this class are: The earliest example of a word derived from an acronym listed by the OED is "abjud" (now " abjad "), formed from the original first four letters of the Arabic alphabet in the late eighteenth century. Some acrostics pre-date this, however, such as

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7068-431: The data processing. The highest accuracy photometric data were provided as a by-product of the main mission astrometric observations. They were made in a broad-band visible light passband , specific to Hipparcos , and designated H p . The median photometric precision, for H p <9 magnitude, was 0.0015 magnitude , with typically 110 distinct observations per star throughout the 3.5-year observation period. As part of

7182-587: The data reduction and catalogue production, new variables were identified and designated with appropriate variable star designations . Variable stars were classified as periodic or unsolved variables; the former were published with estimates of their period, variability amplitude, and variability type. In total some 11,597 variable objects were detected, of which 8,237 were newly classified as variable. There are, for example, 273 Cepheid variables , 186 RR Lyr variables , 108 Delta Scuti variables , and 917 eclipsing binary stars . The star mapper observations, constituting

7296-438: The dictionary entries and style guide recommendations regarding the term acronym through the twentieth century did not explicitly acknowledge or support the expansive sense. The Merriam–Webster's Dictionary of English Usage from 1994 is one of the earliest publications to advocate for the expansive sense, and all the major dictionary editions that include a sense of acronym equating it with initialism were first published in

7410-621: The direction to the Sun. The spacecraft spun around its Z-axis at the rate of 11.25 revolutions/day (168.75 arc-sec/s) at an angle of 43° to the Sun . The Z-axis rotated about the Sun-satellite line at 6.4 revolutions/year. The spacecraft consisted of two platforms and six vertical panels, all made of aluminum honeycomb. The solar array consisted of three deployable sections, generating around 300 W in total. Two S-band antennas were located on

7524-410: The discrepancy between the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by Hipparcos and the distance of 133.5 ± 1.2 pc derived with other techniques was confirmed by parallax measurements made using VLBI , which gave 136.2 ± 1.2 pc , the most accurate and precise distance yet presented for the cluster. Another distance debate set-off by Hipparcos is for the distance to

7638-515: The effects of the Earth 's atmosphere , but were compounded by complex optical terms, thermal and gravitational instrument flexures, and the absence of all-sky visibility. A formal proposal to make these exacting observations from space was first put forward in 1967. The mission was originally proposed to the French space agency CNES , which considered it too complex and expensive for a single national programme and recommended that it be proposed in

7752-664: The exclusive sense for acronym and its earliest citation was from 1943. In early December 2010, Duke University researcher Stephen Goranson published a citation for acronym to the American Dialect Society e-mail discussion list which refers to PGN being pronounced "pee-gee-enn", antedating English language usage of the word to 1940. Linguist Ben Zimmer then mentioned this citation in his December 16, 2010 " On Language " column about acronyms in The New York Times Magazine . By 2011,

7866-763: The final word if spelled out in full. A classic example is "Member of Parliament", which in plural is "Members of Parliament". It is possible then to abbreviate this as "M's P", which was fairly common in mid-twentieth-century Australian news writing (or similar ), and used by former Australian Prime Minister Ben Chifley . This usage is less common than forms with "s" at the end, such as "MPs", and may appear dated or pedantic. In common usage, therefore, "weapons of mass destruction" becomes "WMDs", "prisoners of war" becomes "POWs", and "runs batted in" becomes "RBIs". Abbreviations that come from single, rather than multiple, words – such as "TV" ("television") – are usually pluralized without apostrophes ("two TVs"); most writers feel that

7980-464: The first letter of acronyms, reserving all-caps styling for initialisms, writing the pronounced acronyms "Nato" and "Aids" in mixed case, but the initialisms "USA" and "FBI" in all caps. For example, this is the style used in The Guardian , and BBC News typically edits to this style (though its official style guide, dating from 2003, still recommends all-caps ). The logic of this style is that

8094-455: The five astrometric parameters (Hp<9 magnitude) exceeded the original mission goals, and are between 0.6 and 1.0 mas. Some 20,000 distances were determined to better than 10%, and 50,000 to better than 20%. The inferred ratio of external to standard errors is ≈1.0–1.2, and estimated systematic errors are below 0.1 mas. The number of solved or suspected double or multiple stars is 23,882. Photometric observations yielded multi-epoch photometry with

8208-405: The global orientation of that system but without its regional errors. Whilst of enormous astronomical importance, double stars and multiple stars provided considerable complications to the observations (due to the finite size and profile of the detector's sensitive field of view) and to the data analysis. The data processing classified the astrometric solutions as follows: If a binary star has

8322-837: The instrument switching mechanisms from Oerlikon-Contraves in Zürich , Switzerland; the image dissector tube and photomultiplier detectors assembled by the Dutch Space Research Organisation ( SRON ) in the Netherlands; the refocusing assembly mechanism designed by TNO-TPD in Delft , Netherlands; the electrical power subsystem from British Aerospace in Bristol , United Kingdom; the structure and reaction control system from Daimler-Benz Aerospace in Bremen , Germany;

8436-435: The king". In English, abbreviations have previously been marked by a wide variety of punctuation . Obsolete forms include using an overbar or colon to show the ellipsis of letters following the initial part. The forward slash is still common in many dialects for some fixed expressions—such as in w/ for "with" or A/C for " air conditioning "—while only infrequently being used to abbreviate new terms. The apostrophe

8550-500: The label "usage problem". However, many English language dictionaries, such as the Collins COBUILD Advanced Dictionary , Cambridge Advanced Learner's Dictionary , Macmillan Dictionary , Longman Dictionary of Contemporary English , New Oxford American Dictionary , Webster's New World Dictionary , and Lexico from Oxford University Press do not acknowledge such a sense. Most of

8664-836: The language to changing circumstances. In this view, the modern practice is just the "proper" English of the current generation of speakers, much like the earlier abbreviation of corporation names on ticker tape or newspapers. Exact pronunciation of "word acronyms" (those pronounced as words rather than sounded out as individual letters) often vary by speaker population. These may be regional, occupational, or generational differences, or simply personal preference. For instance, there have been decades of online debate about how to pronounce GIF ( / ɡ ɪ f / or / dʒ ɪ f / ) and BIOS ( / ˈ b aɪ oʊ s / , / ˈ b aɪ oʊ z / , or / ˈ b aɪ ɒ s / ). Similarly, some letter-by-letter initialisms may become word acronyms over time, especially in combining forms: IP for Internet Protocol

8778-432: The location of the observer at each epoch of observation, and were supplied by an appropriate Earth ephemeris combined with accurate satellite ranging. Corrections due to special relativity ( stellar aberration ) made use of the corresponding satellite velocity. Modifications due to general relativistic light bending were significant (4 milliarc-sec at 90° to the ecliptic) and corrected for deterministically assuming γ=1 in

8892-410: The majority of stars means that the angular measurements made, astrometrically, in the plane of the sky, cannot generally be converted into true space velocities in the plane of the sky. For this reason, astrometry characterises the transverse motions of stars in angular measure (e.g. arcsec per year) rather than in km/s or equivalent. Similarly, the typical absence of reliable radial velocities means that

9006-726: The masses of brown dwarfs ; the characterisation of extra-solar planets and their host stars; the height of the Sun above the Galactic mid-plane; the age of the Universe ; the stellar initial mass function and star formation rates; and strategies for the search for extraterrestrial intelligence . The high-precision multi-epoch photometry has been used to measure variability and stellar pulsations in many classes of objects. The Hipparcos and Tycho catalogues are now routinely used to point ground-based telescopes, navigate space missions, and drive public planetaria. Since 1997, several thousand scientific papers have been published making use of

9120-488: The middle of sentences for proper nouns; when following the AMA Manual of Style , this would instead be rendered as "the onset of congestive heart failure (CHF)". Tycho-2 Catalogue The Tycho-2 Catalogue is an astronomical catalogue of more than 2.5 million of the brightest stars . The astrometric reference catalogue contain positions, proper motions , and two-color photometric data for 2,539,913 of

9234-466: The more general "x" can be used to replace an unspecified number of letters. Examples include "Crxn" for "crystallization" and the series familiar to physicians for history , diagnosis , and treatment ("hx", "dx", "tx"). Terms relating to a command structure may also sometimes use this formatting, for example gold, silver, and bronze levels of command in UK policing being referred to as Gx, Sx, and Bx. There

9348-458: The name of the ancient Greek astronomer Hipparchus , who is considered the founder of trigonometry and the discoverer of the precession of the equinoxes (due to the Earth wobbling on its axis). The spacecraft carried a single all-reflective, eccentric Schmidt telescope , with an aperture of 29 cm (11 in). A special beam-combining mirror superimposed two fields of view, 58° apart, into

9462-469: The nearest stars with the largest radial velocities and proper motions, but was accounted for in the 21 cases for which the accumulated positional effect over two years exceeds 0.1 milliarc-sec. Radial velocities for Hipparcos Catalogue stars, to the extent that they are presently known from independent ground-based surveys, can be found from the astronomical database of the Centre de données astronomiques de Strasbourg . The absence of reliable distances for

9576-474: The observation of around 400,000 stars, the resulting Tycho Catalogue comprised just over 1 million stars, with a subsequent analysis extending this to the Tycho-2 Catalogue of about 2.5 million stars. The attitude of the spacecraft about its center of gravity was controlled to scan the celestial sphere in a regular precessional motion maintaining a constant inclination between the spin axis and

9690-420: The observation of some 100,000 stars, with an astrometric accuracy of about 0.002 arc-sec, the final Hipparcos Catalogue comprised nearly 120,000 stars with a median accuracy of slightly better than 0.001 arc-sec (1 milliarc-sec). An additional photomultiplier system viewed a beam splitter in the optical path and was used as a star mapper. Its purpose was to monitor and determine the satellite attitude, and in

9804-409: The observations were as follows: The Hipparcos satellite was financed and managed under the overall authority of the European Space Agency (ESA). The main industrial contractors were Matra Marconi Space (now EADS Astrium ) and Alenia Spazio (now Thales Alenia Space ). Other hardware components were supplied as follows: the beam-combining mirror from REOSC at Saint-Pierre-du-Perray , France;

9918-459: The on-board software and calibration. The Hipparcos satellite was launched (with the direct broadcast satellite TV-Sat 2 as co-passenger) on an Ariane 4 launch vehicle , flight V33, from Centre Spatial Guyanais , Kourou , French Guiana, on 8 August 1989. Launched into a geostationary transfer orbit (GTO), the Mage-2 apogee boost motor failed to fire, and the intended geostationary orbit

10032-729: The plural of 'pages', or mss. for manuscripts . The most common capitalization scheme seen with acronyms is all-uppercase ( all caps ). Small caps are sometimes used to make the run of capital letters seem less jarring to the reader. For example, the style of some American publications, including the Atlantic Monthly and USA Today , is to use small caps for acronyms longer than three letters; thus "U.S." and " FDR " in normal caps, but " nato " in small caps. The acronyms " AD " and " BC " are often smallcapped as well, as in: "From 4004 bc to ad 525 ". Where an acronym has linguistically taken on an identity as regular word,

10146-399: The process, to gather photometric and astrometric data of all stars down to about 11th magnitude. These measurements were made in two broad bands approximately corresponding to B and V in the (Johnson) UBV photometric system . The positions of these latter stars were to be determined to a precision of 0.03 arc-sec, which is a factor of 25 less than the main mission stars. Originally targeting

10260-483: The pronunciation is reflected graphically by the capitalization scheme. However, it conflicts with conventional English usage of first-letter upper-casing as a marker of proper names in many cases; e.g. AIDS stands for acquired immuno-deficiency syndrome which is not a proper name, while Aids is in the style of one. Some style manuals also base the letters' case on their number. The New York Times , for example, keeps "NATO" in all capitals (while several guides in

10374-685: The publication of the 3rd edition of the Oxford English Dictionary added the expansive sense to its entry for acronym and included the 1940 citation. As the Oxford English Dictionary structures the senses in order of chronological development, it now gives the "initialism" sense first. English language usage and style guides which have entries for acronym generally criticize the usage that refers to forms that are not pronounceable words. Fowler's Dictionary of Modern English Usage says that acronym "denotes abbreviations formed from initial letters of other words and pronounced as

10488-693: The resulting Hipparcos celestial reference frame (HCRF) coincides, to within observational uncertainties, with the International Celestial Reference Frame (ICRF), and representing the best estimates at the time of the catalogue completion (in 1996). The HCRF is thus a materialisation of the International Celestial Reference System (ICRS) in the optical domain. It extends and improves the J2000 ( FK5 ) system, retaining approximately

10602-431: The resulting rigid reference frame was transformed to an inertial frame of reference linked to extragalactic sources. This allows surveys at different wavelengths to be directly correlated with the Hipparcos stars, and ensures that the catalogue proper motions are, as far as possible, kinematically non-rotating. The determination of the relevant three solid-body rotation angles, and the three time-dependent rotation rates,

10716-501: The revised analysis. This has been contested by various other recent work, placing the mean cluster distance at around 130 parsecs. According to a 2012 paper, the anomaly was due to the use of a weighted mean when there is a correlation between distances and distance errors for stars in clusters. It is resolved by using an unweighted mean. There is no systematic bias in the Hipparcos data when it comes to star clusters. In August 2014,

10830-512: The satellite observations and data processing, the Hipparcos mission cost about €600 million (in year 2000 economic conditions), and its execution involved some 200 European scientists and more than 2,000 individuals in European industry. The satellite observations relied on a pre-defined list of target stars. Stars were observed as the satellite rotated, by a sensitive region of the image dissector tube detector. This pre-defined star list formed

10944-514: The satellite, were not included in the published Hipparcos Catalogue . Constraints on total observing time, and on the uniformity of stars across the celestial sphere for satellite operations and data analysis, led to an Input Catalogue of some 118,000 stars. It merged two components: first, a survey of around 58,000 objects as complete as possible to the following limiting magnitudes: V<7.9 + 1.1sin|b| for spectral types earlier than G5, and V<7.3 + 1.1sin|b| for spectral types later than G5 (b

11058-524: The scientific teams in June 1997. A more extensive analysis of the star mapper (Tycho) data extracted additional faint stars from the data stream. Combined with old photographic plate observations made several decades earlier as part of the Astrographic Catalogue programme, the Tycho-2 Catalogue of more than 2.5 million stars (and fully superseding the original Tycho Catalogue) was published in 2000. The Hipparcos and Tycho-1 Catalogues were used to create

11172-470: The sides of railroad cars (e.g., "Richmond, Fredericksburg and Potomac Railroad" → "RF&P"); on the sides of barrels and crates; and on ticker tape and newspaper stock listings (e.g. American Telephone and Telegraph Company → AT&T). Some well-known commercial examples dating from the 1890s through 1920s include " Nabisco " ("National Biscuit Company"), " Esso " (from "S.O.", from " Standard Oil "), and " Sunoco " ("Sun Oil Company"). Another field for

11286-1001: The solar arrays and thermal control system from Fokker Space System in Leiden , Netherlands; the data handling and telecommunications system from Saab Ericsson Space in Gothenburg , Sweden; and the apogee boost motor from SEP in France. Groups from the Institut d'Astrophysique in Liège , Belgium and the Laboratoire d'Astronomie Spatiale in Marseille , France, contributed optical performance, calibration and alignment test procedures; Captec in Dublin . Ireland, and Logica in London contributed to

11400-758: The spherical, folding and relay mirrors from Carl Zeiss AG in Oberkochen , Germany; the external straylight baffles from CASA in Madrid , Spain; the modulating grid from CSEM in Neuchâtel , Switzerland; the mechanism control system and the thermal control electronics from Dornier Satellite Systems in Friedrichshafen , Germany; the optical filters, the experiment structures and the attitude and orbit control system from Matra Marconi Space in Vélizy , France;

11514-420: The star Polaris. Hipparcos data is recently being used together with Gaia data. Especially the comparison of the proper motion of stars from both spacecraft is being used to search for hidden binary companions. Hipparcos-Gaia data is also used to measure the dynamical mass of known binaries, such as substellar companions. Hipparcos-Gaia data was used to measure the mass of the exoplanet Beta Pictoris b and

11628-476: The term acronym only for forms pronounced as a word, and using initialism or abbreviation for those that are not. Some sources acknowledge the usage, but vary in whether they criticize or forbid it, allow it without comment, or explicitly advocate it. Some mainstream English dictionaries from across the English-speaking world affirm a sense of acronym which does not require being pronounced as

11742-502: The terms as mutually exclusive. Other guides outright deny any legitimacy to the usage: Bryson's Dictionary of Troublesome Words says "Abbreviations that are not pronounced as words (IBM, ABC, NFL) are not acronyms; they are just abbreviations." Garner's Modern American Usage says "An acronym is made from the first letters or parts of a compound term. It's read or spoken as a single word, not letter by letter." The New York Times Manual of Style and Usage says "Unless pronounced as

11856-431: The top and bottom of the spacecraft, providing an omni-directional downlink data rate of 24  kbit/s . An attitude and orbit-control subsystem (comprising 5- newton hydrazine thrusters for course manoeuvres, 20-millinewton cold gas thrusters for attitude control, and gyroscopes for attitude determination) ensured correct dynamic attitude control and determination during the operational lifetime. Some key features of

11970-424: The transverse space motion (when known) is, in any case, only a component of the complete, three-dimensional, space velocity. The final Hipparcos Catalogue was the result of the critical comparison and merging of the two (NDAC and FAST consortia) analyses, and contains 118,218 entries (stars or multiple stars), corresponding to an average of some three stars per square degree over the entire sky. Median precision of

12084-570: The twenty-first century. The trend among dictionary editors appears to be towards including a sense defining acronym as initialism : the Merriam-Webster's Collegiate Dictionary added such a sense in its 11th edition in 2003, and both the Oxford English Dictionary and The American Heritage Dictionary added such senses in their 2011 editions. The 1989 edition of the Oxford English Dictionary only included

12198-613: The two catalogues improved the accuracy of proper motions by about an order of magnitude. Tycho-2 now supersedes the ACT. Proper motions precise to about 2.5 milliarcseconds per year are given as derived from a comparison with the Astrographic Catalogue (AC 2000) and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system . There were only about 100,000 stars for which proper motion could not be derived. For stars brighter than Vt=9,

12312-502: The various techniques generally agreed to within 10 milliarc-sec in the orientation and 1 milliarc-sec/year in the rotation of the system. From appropriate weighting, the coordinate axes defined by the published catalogue are believed to be aligned with the extragalactic radio frame to within ±0.6 milliarc-sec at the epoch J1991.25, and non-rotating with respect to distant extragalactic objects to within ±0.25 milliarc-sec/yr. The Hipparcos and Tycho Catalogues were then constructed such that

12426-536: The whole range of linguistic registers is relatively new in most languages, becoming increasingly evident since the mid-twentieth century. As literacy spread and technology produced a constant stream of new and complex terms, abbreviations became increasingly convenient. The Oxford English Dictionary ( OED ) records the first printed use of the word initialism as occurring in 1899, but it did not come into general use until 1965, well after acronym had become common. In English, acronyms pronounced as words may be

12540-425: The word " an achro nym ", which is a type of misnomer. Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, "pre-WWII politics", "post-NATO world", " DNase ". In some cases a derived acronym may also be expressed in mixed case. For example, " messenger RNA " and " transfer RNA " become "mRNA" and "tRNA". Some publications choose to capitalize only

12654-517: Was conducted and completed in advance of the catalogue publication. This resulted in an accurate but indirect link to an inertial, extragalactic, reference frame. A variety of methods to establish this reference frame link before catalogue publication were included and appropriately weighted: interferometric observations of radio stars by VLBI networks, MERLIN and Very Large Array (VLA); observations of quasars relative to Hipparcos stars using charge-coupled device (CCD), photographic plates, and

12768-511: Was done with a full space between every full word (e.g. A. D. , i. e. , and e. g. for " Anno Domini ", " id est ", and " exempli gratia "). This even included punctuation after both Roman and Arabic numerals to indicate their use in place of the full names of each number (e.g. LII. or 52. in place of "fifty-two" and "1/4." or "1./4." to indicate "one-fourth"). Both conventions have fallen out of common use in all dialects of English, except in places where an Arabic decimal includes

12882-449: Was little to no naming , conscious attention, or systematic analysis until relatively recent times. Like retronymy, it became much more common in the twentieth century than it had formerly been. Ancient examples of acronymy (before the term "acronym" was invented) include the following: During the mid- to late nineteenth century, acronyms became a trend among American and European businessmen: abbreviating corporation names, such as on

12996-462: Was never achieved. However, with the addition of further ground stations, in addition to ESA operations control centre at European Space Operations Centre (ESOC) in Germany, the satellite was successfully operated in its geostationary transfer orbit (GTO) for almost 3.5 years. All of the original mission goals were, eventually, exceeded. Including an estimate for the scientific activities related to

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