An observer is one who engages in observation or in watching an experiment. Observer may also refer to:

Computer science and information theory

* In

information theory Information theory is the scientific study of the quantification (science), quantification, computer data storage, storage, and telecommunication, communication of information. The field was originally established by the works of Harry Nyquist a ...

, any system which receives information from an object *

State observer In control theory, a state observer or state estimator is a system that provides an estimate of the internal state of a given real system, from measurements of the input and output of the real system. It is typically computer-implemented, and pr ...

in control theory, a system that models a real system in order to provide an estimate of its internal state *

Observer pattern In software design and engineering, the observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by ca ...

, a design pattern used in computer programming

Fiction

* ''Observer'' (video game), a cyberpunk horror video game * Observer (''Mystery Science Theater 3000''), a fictional television character * Observers, beings in the television show ''Fringe''

Military

Air observer An air observer or aerial observer is an aircrew member whose duties are predominantly reconnaissance. The term originated in the First World War in the British Royal Flying Corps, and was maintained by its successor, the Royal Air Force. An ai ...

, an aircrew member *

Artillery observer An artillery observer, artillery spotter or forward observer (FO) is responsible for directing artillery and mortar fire onto a target. It may be a ''forward air controller'' (FAC) for close air support (CAS) and spotter for naval gunfire su ...

, a front line personnel who directs fire discipline for artillery strikes *

Royal Observer Corps The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 December ...

, a civil defence organisation, originally tasked with reporting enemy aircraft * Observer, a non-participating officer, or

umpire An umpire is an official in a variety of sports and competition, responsible for enforcing the rules of the sport, including sportsmanship decisions such as ejection. The term derives from the Old French nonper, ''non'', "not" and ''per'', ...

, tasked with observing the actions of soldiers during a field training or military exercise

Music

* "Observer", a song by Gary Numan on his album '' The Pleasure Principle'' * "The Observer", a track from The Flaming Lips' 1999 album ''

The Soft Bulletin ''The Soft Bulletin'' is the ninth studio album by American rock band the Flaming Lips, released by Warner Bros. Records on May 17, 1999, in the United Kingdom, and on June 22, 1999, in the United States. The album was released to widespread accla ...

'' * The Observers, an alternative name for reggae session band

Soul Syndicate Soul Syndicate, originally called the Rhythm Raiders, were one of the top reggae session bands in Jamaica from the early 1970s to the mid-1980s. History In the first half of the 1970s the band from the Greenwich Farm area of Kingston recorded ...

Niney the Observer Winston Holness, better known as Niney the Observer (born George Boswell, 1951, Montego Bay, Jamaica),Thompson, Dave (2002), ''Reggae & Caribbean Music'', Backbeat Books, . is a Jamaican record producer and singer who was a key figure in the cre ...

(born 1951), Jamaican record producer and singer

Publications

Observer.com ''The New York Observer'' was a weekly newspaper printed from 1987 to 2016, when it ceased print publication and became the online-only newspaper ''Observer''. The media site focuses on culture, real estate, media, politics and the entertainmen ...

, an online-only version of the weekly newspaper ''The New York Observer'' * ''Sunday Observer'' (Sri Lanka), a weekly newspaper * ''Observer'' (APS), a member magazine of Association for Psychological Science * ''The Observer'' (disambiguation), any of various periodicals

Science

* Observer (general relativity) *

Observer (meteorological) A meteorological observer, or weather observer, is a person authorized by a weather authority to make or record meteorological observations. They are technicians who are responsible for the accurate observation, rapid measurement, timely collectio ...

Observer (physics) General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. G ...

Observer (quantum physics) Some interpretations of quantum mechanics posit a central role for an observer of a quantum phenomenon. The quantum mechanical observer is tied to the issue of observer effect, where a measurement necessarily requires interacting with the physical o ...

Observer (special relativity) In special relativity, an observer is a frame of reference from which a set of objects or events are being measured. Usually this is an inertial reference frame or "inertial observer". Less often an observer may be an arbitrary non-inertial refere ...

Observational astronomy Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical m ...

Other uses

Observer status Observer status is a privilege granted by some organizations to non-members to give them an ability to participate in the organization's activities. Observer status is often granted by intergovernmental organizations (IGO) to non-member parties and ...

, granted by an organization to allow a non-member limited participation * An election observer, one who assists in

election monitoring Election monitoring involves the observation of an election by one or more independent parties, typically from another country or from a non-governmental organization (NGO). The monitoring parties aim primarily to assess the conduct of an electi ...

* A game official sometimes used in the sport

Ultimate Ultimate or Ultimates may refer to: Arts, entertainment, and media Music Albums * ''Ultimate'' (Jolin Tsai album) * ''Ultimate'' (Pet Shop Boys album) *''Ultimate!'', an album by The Yardbirds *''The Ultimate (Bryan Adams Album)'', a compilatio ...

* The Observer type in the

Enneagram of Personality The Enneagram of Personality, or simply the Enneagram (from the Greek words meaning "nine"and meaning something "written" or "drawn", is a model of the Psyche (psychology), human psyche which is principally understood and taught as a ...

model *

Donald Alaster Macdonald Donald Alaster Macdonald (6 June 1859 – 23 November 1932) was an Australian journalist and nature writer, writing under the pen names including 'Observer' and 'Gnuyang' (gossip).Hugh Anderson,Macdonald, Donald Alaster (1859–1932), '' Austr ...

(1859–1932), Australian journalist who wrote under the pseudonym 'Observer'