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49-721: The river flows north of the Arctic Circle , in the northern limits of the Central Siberian Plateau and the North Siberian Lowland . The area is very cold and desolate, devoid of settlements. The Kuonamka Formation is a Cambrian large igneous province in the northeastern Siberian platform . The Malaya Kuonamka "Little Kuonamka" is the second largest tributary of the Anabar. The river has its source in an elevated swamp at an altitude of 375 m (1,230 ft) in

98-529: 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

147-495: 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

196-687: 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

245-459: 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"

294-553: 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 ,

343-422: 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

392-481: 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

441-400: 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

490-455: 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

539-420: 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,

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588-431: 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

637-520: 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

686-520: 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

735-468: 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,

784-461: Is ⁠ 1 / 360 ⁠ of a turn, or complete rotation , one arcminute is ⁠ 1 / 21 600 ⁠ of 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

833-513: Is visible at local midnight , and at least once the centre is not visible at local noon . Directly on the Arctic Circle these events occur, in principle, exactly once per year: at the June and December solstices , respectively. However, because of atmospheric refraction and mirages , and also because the sun appears as a disk and not a point, part of the midnight sun is visible, on the night of

882-434: 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

931-486: 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

980-403: Is frozen between late September and late May. The longest tributaries are the 223 kilometres (139 mi) long Usumuun (Усумуун), the 217 kilometres (135 mi) long Delinde (Дьэлиндэ), as well as the 198 kilometres (123 mi) long Maspaaki (Маспаакы) from the right. The main fish species in the river are grayling , taimen and whitefish . Arctic Circle The Arctic Circle

1029-423: 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);

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1078-671: Is one of the two polar circles , and the most northerly of the five major circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern equivalent is the Antarctic Circle . The Arctic Circle marks the southernmost latitude at which, on the winter solstice (which is the shortest day of the year) in the Northern Hemisphere , the Sun will not rise all day, and on the Northern Hemisphere's summer solstice (which

1127-496: 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

1176-621: 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

1225-456: Is the longest day of the year), the Sun will not set. These phenomena are referred to as polar night and midnight sun respectively, and the further north one progresses, the more pronounced these effects become. For example, in the Russian port city of Murmansk , three degrees above the Arctic Circle, the Sun does not rise above the horizon for 40 successive days in midwinter. The position of

1274-585: The Arctic Ocean , the Scandinavian Peninsula , North Asia , Northern America , and Greenland. The land within the Arctic Circle is divided among eight countries: Norway, Sweden, Finland, Russia, the United States ( Alaska ), Canada ( Yukon , Northwest Territories , and Nunavut ), Denmark (Greenland), and Iceland (where it passes through the small offshore island of Grímsey ). The climate north of

1323-498: The Greek word ἀρκτικός ( arktikos : "near the Bear , northern") and that from the word ἄρκτος ( arktos : " bear "). The Arctic Circle is the southernmost latitude in the Northern Hemisphere at which the centre of the Sun can remain continuously above or below the horizon for twenty-four hours; as a result, at least once each year at any location within the Arctic Circle the centre of the Sun

1372-480: 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

1421-400: 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

1470-515: The Arctic Circle is generally cold, but the coastal areas of Norway have a generally mild climate as a result of the Gulf Stream , which makes the ports of northern Norway and northwest Russia ice-free all year long. In the interior, summers can be quite warm, while winters are extremely cold. For example, summer temperatures in Norilsk , Russia will sometimes reach as high as 30 °C (86 °F), while

1519-481: The Arctic Circle is not fixed and currently runs 66°33′50.2″ north of the Equator . Its latitude depends on the Earth's axial tilt , which fluctuates within a margin of more than 2° over a 41,000-year period, owing to tidal forces resulting from the orbit of the Moon . Consequently, the Arctic Circle is currently drifting northwards at a speed of about 14.5 m (48 ft) per year. The word arctic comes from

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1568-587: The Arctic Circle with about 5,000 inhabitants. The largest such community in Canada is Inuvik in the Northwest Territories , with 3,137 inhabitants. Download coordinates as: The Arctic Circle is roughly 16,000 km (9,900 mi) in circumference. The area north of the Circle is about 20,000,000 km (7,700,000 sq mi) and covers roughly 4% of Earth's surface. The Arctic Circle passes through

1617-462: The Arctic Circle, lying 6 km (4 mi) south of the line. Salekhard (51,186) in Russia is the only city in the world located directly on the Arctic Circle. In contrast, the largest North American community north of the Arctic Circle, Sisimiut ( Greenland ), has approximately 5,600 inhabitants. In the United States, Utqiagvik, Alaska (formerly known as Barrow) is the largest settlement north of

1666-451: 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

1715-596: 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,

1764-471: 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

1813-451: 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

1862-628: 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,

1911-529: The eastern side of the Anabar Plateau. Together with the 559 km (347 mi) long Bolshaya Kuonamka "Big Kuonamka" to the west, it is one of the two rivers that form the Anabar at their confluence. In their last stretch both rivers flow roughly northwards. Finally they meet where the Anabar river proper begins, 380 km (240 mi) from its mouth in the Laptev Sea. The river is fed by rain and snow. It

1960-405: 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

2009-411: The northern summer solstice , at a latitude of about 50 minutes of arc (′) (90 km (56 mi)) south of the Arctic Circle. Similarly, on the day of the northern winter solstice , part of the Sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level ; those limits increase with elevation above sea level , although in mountainous regions there is often no direct view of

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2058-403: 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

2107-470: 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

2156-411: 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

2205-667: The symbol ″ , is ⁠ 1 / 60 ⁠ of an arcminute, ⁠ 1 / 3600 ⁠ of 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;

2254-419: 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

2303-507: The true horizon. The largest communities north of the Arctic Circle are situated in Russia, Norway, and Sweden: Murmansk (population 295,374) and Norilsk (178,018) in Russia; Tromsø (75,638) in Norway, Vorkuta (58,133) in Russia, Bodø (52,357) and Harstad (24,703) in Norway; and Kiruna , Sweden (22,841). Rovaniemi (62,667) in Finland is the largest settlement in the immediate vicinity of

2352-413: The winter temperatures frequently fall below −50 °C (−58 °F). Starting at the prime meridian and heading eastwards, the Arctic Circle passes through: 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

2401-446: 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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