In mathematics, the slope or gradient of a line is a number that describes both the direction and the steepness of the line. Slope is often denoted by the letter m; there is no clear answer to the question why the letter m is used for slope, but its earliest use in English appears in O'Brien (1844) who wrote the equation of a straight line as "y = mx + b" and it can also be found in Todhunter (1888) who wrote it as "y = mx + c".
In photography, angle of view (AOV) describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view.
A proscenium is the metaphorical vertical plane of space in a theatre, usually surrounded on the top and sides by a physical proscenium arch and on the bottom by the stage floor itself, which serves as the frame into which the audience observes from a more or less unified angle the events taking place upon the stage during a theatrical performance. The concept of the fourth wall of the theatre stage space that faces the audience is essentially the same.
The grade of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of "tilt". Often slope is calculated as a ratio of "rise" to "run", or as a fraction in which run is the horizontal distance and rise is the vertical distance.
A spotlight is a powerful stage lighting instrument which projects a bright beam of light onto a performance space. Spotlights are controlled by a spotlight operator who tracks actors around the stage. Spotlights are most commonly used in concerts, musicals and large scale presentations where highlighting a specific mobile individual is critical. Spotlights are sometimes located overhead on catwalks. In some theatres, they may also be located in the control booth or purposely built "spot booths" in addition to the catwalk.
An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a tilt indicator, tilt sensor, tilt meter, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch & roll indicator. Clinometers measure both inclines and declines using three different units of measure: degrees, percent, and topo. Astrolabes are inclinometers that were used for navigation and locating astronomical objects from ancient times to the Renaissance.
The Moon illusion is an optical illusion which causes the Moon to appear larger near the horizon than it does higher up in the sky. It has been known since ancient times and recorded by various cultures. The explanation of this illusion is still debated.
In theatre, blocking is the precise staging of actors to facilitate the performance of a play, ballet, film or opera. Historically, the expectations of staging/blocking have changed substantially over time in Western theater. Prior to the movements toward "realism" that occurred in the 19th century, most staging used a "tableau" approach, in which a stage picture was established whenever characters entered or left the stage, ensuring that leading performers were always shown to their best advantage. In more recent times while nothing has changed about showing leading performers to best advantage there have been changing cultural expectations that have made blocking/staging more complicated. There are also artistic reasons why blocking can be crucial. Through careful use of positioning on the stage, a director or performer can establish or change the significance of a scene. Different artistic principles can inform blocking, including minimalism and naturalism.
In theatre and performing arts, the stage is a designated space for the performance of productions. The stage serves as a space for actors or performers and a focal point for the audience. As an architectural feature, the stage may consist of a platform or series of platforms. In some cases, these may be temporary or adjustable but in theaters and other buildings devoted to such productions, the stage is often a permanent feature.
A theater, theatre or playhouse, is a structure where theatrical works or plays are performed, or other performances such as musical concerts may be produced. A theatre used for opera performances is called an opera house. While a theater is not required for performance, a theater serves to define the performance and audience spaces. The facility is traditionally organized to provide support areas for performers, the technical crew and the audience members.
A fly system, or theatrical rigging system, is a system of rope lines, blocks (pulleys), counterweights and related devices within a theater that enables a stage crew to fly (hoist) quickly, quietly and safely components such as curtains, lights, scenery, stage effects and, sometimes, people. Systems are typically designed to fly components between clear view of the audience and out of view, into the large opening, known as the fly loft, above the stage.
In building construction, roof pitch is the steepness of a roof quantified as a ratio or as number of angular degrees that one 'exposure' surface deviates from horizontal level. A roof surface may be either 'functionally flat' or pitched.
Theater drapes and stage curtains are large pieces of cloth that are designed to mask backstage areas of a theater from spectators. They are designed for a variety of specific purposes, moving in different ways and constructed from various fabrics. Many are made from black or other darkly colored, light-absorbing material. Theater drapes represent a portion of any production's soft goods, a category comprising any non-wardrobe, cloth-based element of the stage or scenery. Theater curtains are often pocketed at the bottom to hold weighty chain or to accept pipes to remove their fullness and stretch them tight.
A rake is an angle of slope measured from horizontal, or in some contexts from a vertical line 90° perpendicular to horizontal.
Bicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail. These parameters have a major influence on how a bike handles.
A line array is a loudspeaker system that is made up of a number of usually identical loudspeaker elements mounted in a line and fed in phase, to create a near-line source of sound. The distance between adjacent drivers is close enough that they constructively interfere with each other to send sound waves farther than traditional horn-loaded loudspeakers, and with a more evenly distributed sound output pattern.
The Cockpit Theatre is a fringe theatre in Marylebone, London. Designed by Edward Mendelsohn and built in 1969-70 by the Inner London Education Authority (ILEA) as a community theatre, it is notable as London's first purpose-built Theatre in the round since the Great Fire of London. When ILEA was disbanded in 1990, ownership of the Cockpit was transferred to the London Borough of Westminster, who made it part of the newly renamed City of Westminster College. It remains one of a handful of purpose-built theatre training venues in the capital and is still owned and operated by the City Of Westminster College.
A sightline or visual axis is a normally unobstructed line of sight between an observer or intended observer (spectator) and a subject of interest. The subject may be any definable object taken note of or to be taken note of by the observer, but some fields of study feature specific targets, such as vessels in navigation, marker flags or natural features in surveying, heavenly objects in astronomy, and so on. The term "line" typically presumes that the light by which the observed object is seen travels a straight line. Such is sometimes not the case, as when the light is reflected from a mirror, or when light in space is deflected by a gravitational field.
In astronomy, geography, and related sciences and contexts, a direction or plane passing by a given point is said to be vertical if it contains the local gravity direction at that point. Conversely, a direction or plane is said to be horizontal if it is perpendicular to the vertical direction. In general, something that is vertical can be drawn from up to down, such as the y-axis in the Cartesian coordinate system.
