101 relations: Adaptive optics, Alex Filippenko, Angle, Angular diameter, Angular unit, ASCII, Astrometry, Astronomical seeing, Astronomical unit, Astronomy, Azimuth, Babylonian astronomy, Ball (association football), Betelgeuse, Binary star, Cardinal direction, Cartography, Celestial navigation, Circumflex, Confidence interval, Decimal, Declination, Degree (angle), Degree symbol, Diffraction-limited system, Dime (United States coin), Dimensionless quantity, Ecliptic coordinate system, Eiffel Tower, Epitaxy, Equator, Equatorial coordinate system, Figure of the Earth, Firearm, Gaia (spacecraft), Geographical mile, Global Positioning System, Gradian, Great circle, Horizontal coordinate system, Hubble Space Telescope, Imperial units, Inch, International System of Units, Latitude, Light-year, Longitude, M24 Sniper Weapon System, Marksman, Meridian (geography), ..., Meridian arc, Metes and bounds, Metric prefix, Metric system, Mile, Milliradian, Minute and second of arc, Mosaicity, Nautical mile, Navigation, Neptune, New York City, Non-SI units mentioned in the SI, Ophthalmology, Optical comparator, Optical engineering, Optics, Optometry, Parallax, Parsec, Pluto, Prime (symbol), Prime meridian, Proper motion, R Doradus, Radian, Radix, Reference ellipsoid, Reticle, Rifle, Right ascension, Sea level, Sexagesimal, Shooting range, Shot grouping, Solid angle, Spatiotemporal pattern, Spheroid, Spotting scope, Subtended angle, Supergiant star, Surveying, Telescope, Telescopic sight, Triton (moon), Turn (geometry), Venus, Visual acuity, Visual angle, X-ray crystallography, Yard. Expand index (51 more) » « Shrink index
Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion.
Alexei Vladimir "Alex" Filippenko (born July 25, 1958) is an American astrophysicist and professor of astronomy at the University of California, Berkeley.
In plane geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.
The angular diameter, angular size, apparent diameter, or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view.
Throughout history, angles have been measured in many different units.
ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication.
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.
Astronomical seeing is the blurring and twinkling of astronomical objects like stars due to turbulent mixing in the Earth's atmosphere, causing variations of the optical refractive index.
The astronomical unit (symbol: au, ua, or AU) is a unit of length, roughly the distance from Earth to the Sun.
Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.
An azimuth (from the pl. form of the Arabic noun "السَّمْت" as-samt, meaning "the direction") is an angular measurement in a spherical coordinate system.
The history of astronomy in Mesopotamia, and the world, begins with the Sumerians who developed the earliest writing system—known as cuneiform—around 3500–3200 BC.
A football, soccer ball, or association football ball is the ball used in the sport of association football.
Betelgeuse, also designated Alpha Orionis (α Orionis, abbreviated Alpha Ori, α Ori), is the ninth-brightest star in the night sky and second-brightest in the constellation of Orion.
A binary star is a star system consisting of two stars orbiting around their common barycenter.
The four cardinal directions or cardinal points are the directions north, east, south, and west, commonly denoted by their initials N, E, S, and W. East and west are at right angles to north and south, with east being in the clockwise direction of rotation from north and west being directly opposite east.
Cartography (from Greek χάρτης chartēs, "papyrus, sheet of paper, map"; and γράφειν graphein, "write") is the study and practice of making maps.
Celestial navigation, also known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position.
Christmas is an annual festival commemorating the birth of Jesus Christ,Martindale, Cyril Charles.
The Christmas season, also called the festive season, or the holiday season (mainly in the U.S. and Canada; often simply called the holidays),, is an annually recurring period recognized in many Western and Western-influenced countries that is generally considered to run from late November to early January.
Christmas Eve is the evening or entire day before Christmas Day, the festival commemorating the birth of Jesus.
Christmas traditions vary from country to country.
The circumflex is a diacritic in the Latin, Greek and Cyrillic scripts that is used in the written forms of many languages and in various romanization and transcription schemes.
In statistics, a confidence interval (CI) is a type of interval estimate, computed from the statistics of the observed data, that might contain the true value of an unknown population parameter.
The decimal numeral system (also called base-ten positional numeral system, and occasionally called denary) is the standard system for denoting integer and non-integer numbers.
In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle.
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees.
The degree symbol (°) is a typographical symbol that is used, among other things, to represent degrees of arc (e.g. in geographic coordinate systems), hours (in the medical field), degrees of temperature, alcohol proof, or diminished quality in musical harmony.
The resolution of an optical imaging system a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment.
The dime, in U.S. usage, is a ten-cent coin, one tenth of a United States dollar, labeled formally as "one dime".
In dimensional analysis, a dimensionless quantity is a quantity to which no physical dimension is assigned.
The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions and orbits of Solar System objects.
The Eiffel Tower (tour Eiffel) is a wrought iron lattice tower on the Champ de Mars in Paris, France.
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate.
An equator of a rotating spheroid (such as a planet) is its zeroth circle of latitude (parallel).
The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects.
The figure of the Earth is the size and shape of the Earth in geodesy.
A firearm is a portable gun (a barreled ranged weapon) that inflicts damage on targets by launching one or more projectiles driven by rapidly expanding high-pressure gas produced by exothermic combustion (deflagration) of propellant within an ammunition cartridge.
Gaia is a space observatory of the European Space Agency (ESA) designed for astrometry: measuring the positions and distances of stars with unprecedented precision.
The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator.
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Air Force.
The gradian is a unit of measurement of an angle, equivalent to \frac of a turn, \frac of a degree, or \frac of a radian.
A great circle, also known as an orthodrome, of a sphere is the intersection of the sphere and a plane that passes through the center point of the sphere.
The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane.
The Hubble Space Telescope (HST) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation.
The system of imperial units or the imperial system (also known as British Imperial or Exchequer Standards of 1825) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced.
The inch (abbreviation: in or &Prime) is a unit of length in the (British) imperial and United States customary systems of measurement now formally equal to yard but usually understood as of a foot.
The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement.
In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface.
The light-year is a unit of length used to express astronomical distances and measures about 9.5 trillion kilometres or 5.9 trillion miles.
Longitude, is a geographic coordinate that specifies the east-west position of a point on the Earth's surface.
The M24 Sniper Weapon System (SWS) is the military and police version of the Remington Model 700 rifle, M24 being the model name assigned by the United States Army after adoption as their standard sniper rifle in 1988.
A marksman is a person who is skilled in precision shooting, using accurate precision scoped projectile weapons (in modern days most commonly a designated marksman rifle or a sniper rifle) to shoot at high-value targets at longer-than-usual ranges.
A (geographical) meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude.
In geodesy, a meridian arc measurement is the distance between two points with the same longitude, i.e., a segment of a meridian curve or its length.
Metes and bounds is a system or method of describing land, real property (in contrast to personal property) or real estate.
A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit.
The metric system is an internationally adopted decimal system of measurement.
The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.
A milliradian, often called a mil or mrad, is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian).
A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree.
In crystallography, mosaicity is a measure of the spread of crystal plane orientations.
A nautical mile is a unit of measurement defined as exactly.
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.
Neptune is the eighth and farthest known planet from the Sun in the Solar System.
New Year is the time or day at which a new calendar year begins and the calendar's year count increments by one.
New Year's Day, also called simply New Year's or New Year, is observed on January 1, the first day of the year on the modern Gregorian calendar as well as the Julian calendar.
In the Gregorian calendar, New Year's Eve (also known as Old Year's Day or Saint Sylvester's Day in many countries), the last day of the year, is on 31 December which is the seventh day of Christmastide.
The City of New York, often called New York City (NYC) or simply New York, is the most populous city in the United States.
This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.
Ophthalmology is a branch of medicine and surgery (both methods are used) that deals with the anatomy, physiology and diseases of the eyeball and orbit.
An optical comparator (often called just a comparator in context) is a device that applies the principles of optics to the inspection of manufactured parts.
Optical engineering is the field of study that focuses on applications of optics.
Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.
Optometry is a health care profession which involves examining the eyes and applicable visual systems for defects or abnormalities as well as the medical diagnosis and management of eye disease.
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System.
Pluto (minor planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune.
The prime symbol (′), double prime symbol (&Prime), triple prime symbol (‴), quadruple prime symbol (⁗) etc., are used to designate units and for other purposes in mathematics, the sciences, linguistics and music.
A prime meridian is a meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°.
Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.
R Doradus (HD 29712 or P Doradus) is the name of a red giant Mira variable star in the far-southern constellation Dorado, although visually it appears more closely associated with the constellation Reticulum.
The radian (SI symbol rad) is the SI unit for measuring angles, and is the standard unit of angular measure used in many areas of mathematics.
In mathematical numeral systems, the radix or base is the number of unique digits, including zero, used to represent numbers in a positional numeral system.
In geodesy, a reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.
A reticle, or reticule, also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of a sighting device, such as a telescopic sight in a telescope, a microscope, or the screen of an oscilloscope, to provide references during visual examination.
A rifle is a portable long-barrelled firearm designed for precision shooting, to be held with both hands and braced against the shoulder for stability during firing, and with a barrel that has a helical pattern of grooves ("rifling") cut into the bore walls.
Right ascension (abbreviated RA; symbol) is the angular distance measured only eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point above the earth in question.
Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's oceans from which heights such as elevations may be measured.
Sexagesimal (base 60) is a numeral system with sixty as its base.
A shooting range or firing range or archery range or pistol range or rifle range or shooting gallery or shooting ground is a specialized facility designed for archery or firearms practice.
In shooting sports, a shot grouping, or simply grouping, is the pattern of projectile impacts on a target from multiple shots taken in one shooting session.
In geometry, a solid angle (symbol) is a measure of the amount of the field of view from some particular point that a given object covers.
Spatialtemporal patterns are patterns that occur in a wide range of natural phenoma and are characterized by a spatial and a temporal patterning.
A spheroid, or ellipsoid of revolution, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters.
A spotting scope is a small portable high-power telescope with added optics to present an erect image, optimized for the observation of terrestrial objects.
In geometry, an angle subtended by an arc, line segment, or other curve is one whose two rays pass through the endpoints of the arc.
Supergiants are among the most massive and most luminous stars.
Surveying or land surveying is the technique, profession, and science of determining the terrestrial or three-dimensional positions of points and the distances and angles between them.
A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).
A telescopic sight, commonly called a scope, is an optical sighting device that is based on a refracting telescope.
Triton is the largest natural satellite of the planet Neptune, and the first Neptunian moon to be discovered.
A turn is a unit of plane angle measurement equal to 2pi radians, 360 degrees or 400 gradians.
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days.
Visual acuity (VA) commonly refers to the clarity of vision.
The visual angle is the angle a viewed object subtends at the eye, usually stated in degrees of arc.
X-ray crystallography is a technique used for determining the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions.
The yard (abbreviation: yd) is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches.
2018 has been designated as the third International Year of the Reef by the International Coral Reef Initiative.
2019 (MMXIX) will be a common year starting on Tuesday of the Gregorian calendar, the 2019th year of the Common Era (CE) and Anno Domini (AD) designations, the 19th year of the 3rd millennium, the 19th year of the 21st century, and the 10th and last year of the 2010s decade.
Arc min, Arc minute, Arc of minute, Arc second, Arc seconds, Arc-fourth, Arc-minute, Arc-second, Arc-third, Arcfourth, Arcmin, Arcminute, Arcminutes, Arcsec (angle unit), Arcsec (unit), Arcsecond, Arcseconds, Arcthird, Asec (angle unit), Asec (unit), Fourths (angle), Microarcsecond, Milliarcsecond, Milliarcseconds, Minut (angle), Minute (angle), Minute (arc), Minute of Angle, Minute of Arc, Minute of a circle, Minute of angle, Minute of arc, Minutes (angle), Minutes of angle, Minutes of arc, Moment of angle, Partes minutae primae, Partes minutae secundae, Second (angle), Second (arc), Second of angle, Second of arc, Seconds (angle), Sub-MOA, Thirds (angle), Μas.