55-612: Far Ultraviolet Spectroscopic Explorer ( FUSE , Explorer 77 , and MIDEX-0 ) represented the next generation, high-orbit, ultraviolet space observatory covering the wavelength range of 90.5–119.5 nanometre (nm) of the NASA operated by the Johns Hopkins University Applied Physics Laboratory . FUSE was launched on a Delta II launch vehicle on 24 June 1999, at 15:44:00 UTC , as a part of NASA's Origins Program . FUSE detected light in
110-529: A 1 MOA rifle should be capable, under ideal conditions, of repeatably shooting 1-inch groups at 100 yards. Most higher-end rifles are warrantied by their manufacturer to shoot under a given MOA threshold (typically 1 MOA or better) with specific ammunition and no error on the shooter's part. For example, Remington's M24 Sniper Weapon System is required to shoot 0.8 MOA or better, or be rejected from sale by quality control . Rifle manufacturers and gun magazines often refer to this capability as sub-MOA , meaning
165-405: A Rowland circle design . The light from the four optical channels is dispersed by four spherical, aberration-corrected holographic diffraction gratings, and recorded by two delay-line microchannel plate detectors . Two channels with silicon carbide (SiC) coatings cover the range 90.5–110 nm and two channels with lithium fluoride (LiF) coatings cover the range 100–119.5 nm. Actuators on
220-406: A meter (0.000000001 m) and to 1000 picometres . One nanometre can be expressed in scientific notation as 1 × 10 m and as 1 / 1 000 000 000 m. The nanometre was formerly known as the " millimicrometre " – or, more commonly, the " millimicron " for short – since it is 1 / 1000 of a micrometer . It was often denoted by
275-495: A visual angle of one minute of arc, from a distance of twenty feet . A 20/20 letter subtends 5 minutes of arc total. The deviation from parallelism between two surfaces, for instance in optical engineering , is usually measured in arcminutes or arcseconds. In addition, arcseconds are sometimes used in rocking curve (ω-scan) x ray diffraction measurements of high-quality epitaxial thin films. Some measurement devices make use of arcminutes and arcseconds to measure angles when
330-485: A 99.80 minutes orbital period . Its Explorer program designation is Explorer 77. The primary objective of FUSE was to use high-resolution spectroscopy at far ultraviolet wavelengths to study the origin and evolution of the lightest elements ( hydrogen and deuterium) created shortly after the Big Bang, and the forces and processes involved in the evolution of galaxies , stars and planetary systems . The spacecraft
385-687: A circle with a diameter of 1.047 inches (which is often rounded to just 1 inch) at 100 yards (2.66 cm at 91 m or 2.908 cm at 100 m), a traditional distance on American target ranges . The subtension is linear with the distance, for example, at 500 yards, 1 MOA subtends 5.235 inches, and at 1000 yards 1 MOA subtends 10.47 inches. Since many modern telescopic sights are adjustable in half ( 1 / 2 ), quarter ( 1 / 4 ) or eighth ( 1 / 8 ) MOA increments, also known as clicks , zeroing and adjustments are made by counting 2, 4 and 8 clicks per MOA respectively. For example, if
440-459: A degree) and specify locations within about 120 metres (390 feet). For navigational purposes positions are given in degrees and decimal minutes, for instance The Needles lighthouse is at 50º 39.734’N 001º 35.500’W. Related to cartography, property boundary surveying using the metes and bounds system and cadastral surveying relies on fractions of a degree to describe property lines' angles in reference to cardinal directions . A boundary "mete"
495-570: A degree, 1 / 1 296 000 of a turn, and π / 648 000 (about 1 / 206 264 .8 ) of a radian. These units originated in Babylonian astronomy as sexagesimal (base 60) subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy , optometry , ophthalmology , optics , navigation , land surveying , and marksmanship . To express even smaller angles, standard SI prefixes can be employed;
550-560: A degree/day in the Earth's annual rotation around the Sun, which is off by roughly 1%. The same ratios hold for seconds, due to the consistent factor of 60 on both sides. The arcsecond is also often used to describe small astronomical angles such as the angular diameters of planets (e.g. the angular diameter of Venus which varies between 10″ and 60″); the proper motion of stars; the separation of components of binary star systems ; and parallax ,
605-422: A fraction of a mrad) are collectively called a mrad reticle. If the markings are round they are called mil-dots . In the table below conversions from mrad to metric values are exact (e.g. 0.1 mrad equals exactly 10 mm at 100 metres), while conversions of minutes of arc to both metric and imperial values are approximate. In humans, 20/20 vision is the ability to resolve a spatial pattern separated by
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#1732772904100660-484: A group measuring 0.7 inches followed by a group that is 1.3 inches, this is not statistically abnormal. The metric system counterpart of the MOA is the milliradian (mrad or 'mil'), being equal to 1 ⁄ 1000 of the target range, laid out on a circle that has the observer as centre and the target range as radius. The number of milliradians on a full such circle therefore always is equal to 2 × π × 1000, regardless
715-400: A gun consistently shooting groups under 1 MOA. This means that a single group of 3 to 5 shots at 100 yards, or the average of several groups, will measure less than 1 MOA between the two furthest shots in the group, i.e. all shots fall within 1 MOA. If larger samples are taken (i.e., more shots per group) then group size typically increases, however this will ultimately average out. If a rifle
770-455: A line running from the starting point 85.69 feet in a direction 65° 39′ 18″ (or 65.655°) away from north toward the west. The arcminute is commonly found in the firearms industry and literature, particularly concerning the precision of rifles , though the industry refers to it as minute of angle (MOA). It is especially popular as a unit of measurement with shooters familiar with the imperial measurement system because 1 MOA subtends
825-420: A minute, for example, written as 42° 25.32′ or 42° 25.322′. This notation has been carried over into marine GPS and aviation GPS receivers, which normally display latitude and longitude in the latter format by default. The average apparent diameter of the full Moon is about 31 arcminutes, or 0.52°. One arcminute is the approximate distance two contours can be separated by, and still be distinguished by,
880-431: A modern second. Since antiquity, the arcminute and arcsecond have been used in astronomy : in the ecliptic coordinate system as latitude (β) and longitude (λ); in the horizon system as altitude (Alt) and azimuth (Az); and in the equatorial coordinate system as declination (δ). All are measured in degrees, arcminutes, and arcseconds. The principal exception is right ascension (RA) in equatorial coordinates, which
935-528: A period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth. One nanoarcsecond is about the size of a penny on Neptune 's moon Triton as observed from Earth. Also notable examples of size in arcseconds are: The concepts of degrees, minutes, and seconds—as they relate to the measure of both angles and time—derive from Babylonian astronomy and time-keeping. Influenced by
990-535: A person with 20/20 vision . One arcsecond is the approximate angle subtended by a U.S. dime coin (18 mm) at a distance of 4 kilometres (about 2.5 mi). An arcsecond is also the angle subtended by One milliarcsecond is about the size of a half dollar, seen from a distance equal to that between the Washington Monument and the Eiffel Tower . One microarcsecond is about the size of
1045-468: A precision-oriented firearm's performance will be measured in MOA. This simply means that under ideal conditions (i.e. no wind, high-grade ammo, clean barrel, and a stable mounting platform such as a vise or a benchrest used to eliminate shooter error), the gun is capable of producing a group of shots whose center points (center-to-center) fit into a circle, the average diameter of circles in several groups can be subtended by that amount of arc. For example,
1100-447: A scale of nanometres (see nanoscopic scale ). The nanometre is often used to express dimensions on an atomic scale: the diameter of a helium atom, for example, is about 0.06 nm, and that of a ribosome is about 20 nm. The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum : visible light ranges from around 400 to 700 nm. The ångström , which
1155-439: A turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near 21 600 nmi . A minute of arc is π / 10 800 of a radian . A second of arc , arcsecond (arcsec), or arc second , denoted by the symbol ″ , is 1 / 60 of an arcminute, 1 / 3600 of
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#17327729041001210-434: Is also abbreviated as arcmin or amin . Similarly, double prime ″ (U+2033) designates the arcsecond, though a double quote " (U+0022) is commonly used where only ASCII characters are permitted. One arcsecond is thus written as 1″. It is also abbreviated as arcsec or asec . In celestial navigation , seconds of arc are rarely used in calculations, the preference usually being for degrees, minutes, and decimals of
1265-560: Is called FGS/NIRISS and is a combined Fine Guidance Sensor , spectrograph , and Far Ultraviolet Camera/Spectrograph . Nanometre The nanometre (international spelling as used by the International Bureau of Weights and Measures ; SI symbol: nm ), or nanometer ( American spelling ), is a unit of length in the International System of Units (SI), equal to one billionth ( short scale ) of
1320-486: Is described with a beginning reference point, the cardinal direction North or South followed by an angle less than 90 degrees and a second cardinal direction, and a linear distance. The boundary runs the specified linear distance from the beginning point, the direction of the distance being determined by rotating the first cardinal direction the specified angle toward the second cardinal direction. For example, North 65° 39′ 18″ West 85.69 feet would describe
1375-406: Is detected by two microchannel plate detector intensified double delay-line detectors, whose surfaces are curved to match the curvature of the focal plane. The FUSE observatory was designed for an operational lifetime of three years, although it was hoped that it might remain operational for as long as ten years. NASA since recommended an additional two-year extension beyond the prime mission. FUSE
1430-516: Is equal to 0.1 nm, was formerly used for these purposes. Since the late 1980s, in usages such as the 32 nm and the 22 nm semiconductor node , it has also been used to describe typical feature sizes in successive generations of the ITRS Roadmap for miniaturized semiconductor device fabrication in the semiconductor industry . The CJK Compatibility block in Unicode has
1485-423: Is measured in time units of hours, minutes, and seconds. Contrary to what one might assume, minutes and seconds of arc do not directly relate to minutes and seconds of time, in either the rotational frame of the Earth around its own axis (day), or the Earth's rotational frame around the Sun (year). The Earth's rotational rate around its own axis is 15 minutes of arc per minute of time (360 degrees / 24 hours in day);
1540-503: Is roughly 30 metres (98 feet). The exact distance varies along meridian arcs or any other great circle arcs because the figure of the Earth is slightly oblate (bulges a third of a percent at the equator). Positions are traditionally given using degrees, minutes, and seconds of arcs for latitude , the arc north or south of the equator, and for longitude , the arc east or west of the Prime Meridian . Any position on or above
1595-626: Is that some MOA scopes, including some higher-end models, are calibrated such that an adjustment of 1 MOA on the scope knobs corresponds to exactly 1 inch of impact adjustment on a target at 100 yards, rather than the mathematically correct 1.047 inches. This is commonly known as the Shooter's MOA (SMOA) or Inches Per Hundred Yards (IPHY). While the difference between one true MOA and one SMOA is less than half of an inch even at 1000 yards, this error compounds significantly on longer range shots that may require adjustment upwards of 20–30 MOA to compensate for
1650-485: The Sumerians , the ancient Babylonians divided the Sun's perceived motion across the sky over the course of one full day into 360 degrees. Each degree was subdivided into 60 minutes and each minute into 60 seconds. Thus, one Babylonian degree was equal to four minutes in modern terminology, one Babylonian minute to four modern seconds, and one Babylonian second to 1 / 15 (approximately 0.067) of
1705-400: The milliarcsecond (mas) and microarcsecond (μas), for instance, are commonly used in astronomy. For a three-dimensional area such as on a sphere, square arcminutes or seconds may be used. The prime symbol ′ ( U+ 2032 ) designates the arcminute, though a single quote ' (U+0027) is commonly used where only ASCII characters are permitted. One arcminute is thus written as 1′. It
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1760-451: The Earth's reference ellipsoid can be precisely given with this method. However, when it is inconvenient to use base -60 for minutes and seconds, positions are frequently expressed as decimal fractional degrees to an equal amount of precision. Degrees given to three decimal places ( 1 / 1000 of a degree) have about 1 / 4 the precision of degrees-minutes-seconds ( 1 / 3600 of
1815-606: The Earth's atmosphere but are diffraction limited . For example, the Hubble Space Telescope can reach an angular size of stars down to about 0.1″. Minutes (′) and seconds (″) of arc are also used in cartography and navigation . At sea level one minute of arc along the equator equals exactly one geographical mile (not to be confused with international mile or statute mile) along the Earth's equator or approximately one nautical mile (1,852 metres ; 1.151 miles ). A second of arc, one sixtieth of this amount,
1870-475: The Earth's rotational rate around the Sun (not entirely constant) is roughly 24 minutes of time per minute of arc (from 24 hours in day), which tracks the annual progression of the Zodiac. Both of these factor in what astronomical objects you can see from surface telescopes (time of year) and when you can best see them (time of day), but neither are in unit correspondence. For simplicity, the explanations given assume
1925-555: The FUSE science team and a host of Guest investigators, astronomers from around the world selected by NASA to participate in the FUSE program. Starting 1 April 2003, the FUSE project entered an extended phase of operations which lasted until mid-2007. With funding from NASA, the FUSE satellite continued to be operated as an observatory for the broad astronomical community, with 100% of on-orbit observing time selected by NASA peer review. Some 29 million seconds of science data were obtained during
1980-549: The Primary Mission phase, and a total of nearly 65 million seconds of data were archived from the entire mission. The Extended Mission period presented a number of challenges, especially for satellite operations. Many procedures had to be automated, allowing the project to cut back on staffing and minimize operations costs. As one example, the Satellite Control Center was staffed around the clock during
2035-554: The Prime Mission but transitioned to a 16-hour per day, Monday through Friday staffing profile in the Extended Mission. Less redundancy and less access to ongoing engineering support were consistent with NASA policy for missions in their extended phase, where a higher level of risk is allowed. The FUSE satellite consists of two primary sections, the spacecraft and the science instrument. The spacecraft contains all of
2090-451: The angle, measured in arcseconds, of the object's apparent movement caused by parallax. The European Space Agency 's astrometric satellite Gaia , launched in 2013, can approximate star positions to 7 microarcseconds (μas). Apart from the Sun, the star with the largest angular diameter from Earth is R Doradus , a red giant with a diameter of 0.05″. Because of the effects of atmospheric blurring , ground-based telescopes will smear
2145-628: The bullet drop. If a shot requires an adjustment of 20 MOA or more, the difference between true MOA and SMOA will add up to 1 inch or more. In competitive target shooting, this might mean the difference between a hit and a miss. The physical group size equivalent to m minutes of arc can be calculated as follows: group size = tan( m / 60 ) × distance. In the example previously given, for 1 minute of arc, and substituting 3,600 inches for 100 yards, 3,600 tan( 1 / 60 ) ≈ 1.047 inches. In metric units 1 MOA at 100 metres ≈ 2.908 centimetres. Sometimes,
2200-497: The elements necessary for powering and pointing the satellite, including the Attitude Control System , the solar panels , and communications-electronics and antennas . The observatory is approximately 7.6 m (25 ft) long with a baffle fully deployed. The FUSE science instrument consists of four co-aligned telescope mirrors (~39 × 35 cm (15 × 14 in) clear aperture) based on
2255-460: The far ultraviolet portion of the electromagnetic spectrum , which is mostly unobservable by other telescopes. Its primary mission was to characterize universal deuterium in an effort to learn about the stellar processing times of deuterium left over from the Big Bang . FUSE resides in a low Earth orbit , approximately 760 km (470 mi) in altitude , with an inclination of 24.98° and
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2310-405: The image of a star to an angular diameter of about 0.5″; in poor conditions this increases to 1.5″ or even more. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1″. Techniques exist for improving seeing on the ground. Adaptive optics , for example, can produce images around 0.05″ on a 10 m class telescope. Space telescopes are not affected by
2365-447: The mirror mountings kept the focus to 90% encircled energy within 1.5". A Fine Error Sensor (FES) with a 21' square field maintained the spacecraft pointing stability to 0.5 arcseconds . Each mirror has a corresponding astigmatism -corrected, holographically -ruled diffraction grating , each one on a curved substrate so as to produce four 1.65 m (5 ft 5 in) Rowland circle spectrographs . The dispersed ultraviolet light
2420-403: The point of impact is 3 inches high and 1.5 inches left of the point of aim at 100 yards (which for instance could be measured by using a spotting scope with a calibrated reticle, or a target delineated for such purposes), the scope needs to be adjusted 3 MOA down, and 1.5 MOA right. Such adjustments are trivial when the scope's adjustment dials have a MOA scale printed on them, and even figuring
2475-421: The reaction wheels were unsuccessful. Although the telescope itself remained in excellent condition, the satellite was incapable thereafter of the fine pointing control required to acquire useful science data, and the mission was terminated. Over 400 scientific papers have been written using data from FUSE, with subjects ranging from cool stars to the intergalactic medium . One of the primary science goals of FUSE
2530-470: The right number of clicks is relatively easy on scopes that click in fractions of MOA. This makes zeroing and adjustments much easier: Another common system of measurement in firearm scopes is the milliradian (mrad). Zeroing an mrad based scope is easy for users familiar with base ten systems. The most common adjustment value in mrad based scopes is 1 / 10 mrad (which approximates 1 ⁄ 3 MOA). One thing to be aware of
2585-411: The small change of position of a star or Solar System body as the Earth revolves about the Sun. These small angles may also be written in milliarcseconds (mas), or thousandths of an arcsecond. The unit of distance called the parsec , abbreviated from the par allax angle of one arc sec ond, was developed for such parallax measurements. The distance from the Sun to a celestial object is the reciprocal of
2640-424: The spectrograph apertures, and performing the observations. The scientific data, which was stored in digital form, was radioed to the ground during contact with the ground station. FUSE Science Operations were on hold from 10 December 2001, to approximately the end of January 2002, due to a problem with the pointing system. The last operational reaction wheel on FUSE stopped on 12 July 2007. Attempts to restart any of
2695-420: The symbol U+339A ㎚ SQUARE NM . Minute and second of arc A minute of arc , arcminute ( arcmin ), arc minute , or minute arc , denoted by the symbol ′ , is a unit of angular measurement equal to 1 / 60 of one degree . Since one degree is 1 / 360 of a turn, or complete rotation , one arcminute is 1 / 21 600 of
2750-547: The symbol mμ or, more rarely, as μμ (however, μμ should refer to a millionth of a micron). The name combines the SI prefix nano- (from the Ancient Greek νάνος , nanos , "dwarf") with the parent unit name metre (from Greek μέτρον , [metrοn] Error: {{Lang}}: Non-latn text/Latn script subtag mismatch ( help ) , "unit of measurement"). Nanotechnologies are based on physical processes which occur on
2805-419: The target range. Therefore, 1 MOA ≈ 0.2909 mrad. This means that an object which spans 1 mrad on the reticle is at a range that is in metres equal to the object's linear size in millimetres (e.g. an object of 100 mm subtending 1 mrad is 100 metres away). So there is no conversion factor required, contrary to the MOA system. A reticle with markings (hashes or dots) spaced with a one mrad apart (or
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#17327729041002860-497: Was controlled through a primary ground station antenna located at the University of Puerto Rico at Mayagüez . FUSE brought it over the ground station for less than 10 minutes at a time (on average) for about six or seven orbits in a row, followed by roughly seven or eight orbits without contact. Hence, the satellite had to operate on its own most of the time, moving from target to target, identifying star fields, centering objects in
2915-413: Was launched as a joint NASA-Canada–France project. Only one previous mission, Copernicus (OAO-3), has given this far-ultraviolet region of the electromagnetic spectrum. However, FUSE will provide sensitivity some ten thousand times greater than Copernicus. The first 3.5 years of FUSE operations were dubbed the Primary Mission. During this period, the observing time on FUSE was shared roughly 50–50 between
2970-508: Was to study the abundance of deuterium, an isotope of hydrogen . Because of the large number of atomic absorption and emission lines in the far-ultraviolet, FUSE enabled many studies of galactic, extragalactic, and intergalactic chemistry and chemical evolution. Canada credits work on the FUSE as helping them prepare for making the fine guidance sensors instrument on the James Webb Space Telescope . Canada's contribution
3025-446: Was truly a 1 MOA rifle, it would be just as likely that two consecutive shots land exactly on top of each other as that they land 1 MOA apart. For 5-shot groups, based on 95% confidence , a rifle that normally shoots 1 MOA can be expected to shoot groups between 0.58 MOA and 1.47 MOA, although the majority of these groups will be under 1 MOA. What this means in practice is if a rifle that shoots 1-inch groups on average at 100 yards shoots
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