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# Angular distance

In mathematics (in particular geometry and trigonometry) and all natural sciences (e.g. astronomy and geophysics), the angular distance (angular separation, apparent distance, or apparent separation) between two point objects, as viewed from a location different from either of these objects, is the angle of length between the two directions originating from the observer and pointing toward these two objects. [1]

## Angle

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.

## Angular diameter

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.

## Angular displacement

Angular displacement of a body is the angle in radians (degrees, revolutions) through which a point revolves around a centre or line has been rotated in a specified sense about a specified axis.

## Astronomical object

An astronomical object or celestial object is a naturally occurring physical entity, association, or structure that exists in the observable universe.

## Astronomical unit

The astronomical unit (symbol: au, ua, or AU) is a unit of length, roughly the distance from Earth to the Sun.

## Astronomy

Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.

## Binary star

A binary star is a star system consisting of two stars orbiting around their common barycenter.

## Central angle

Central angles are subtended by an arc between those two points, and the arc length is the central angle of a circle of radius one (measured in radians).

The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects.

## Declination

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.

## Degree (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.

## Distance

Distance is a numerical measurement of how far apart objects are.

## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

## Exoplanet

An exoplanet or extrasolar planet is a planet outside our solar system.

## Geometry

Geometry (from the γεωμετρία; geo- "earth", -metron "measurement") is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space.

## Geophysics

Geophysics is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis.

## Goniometer

A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position.

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.

## Great-circle distance

The great-circle distance or orthodromic distance is the shortest distance between two points on the surface of a sphere, measured along the surface of the sphere (as opposed to a straight line through the sphere's interior).

## Hour angle

In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere.

## Length

In geometric measurements, length is the most extended dimension of an object.

## Mathematics

Mathematics (from Greek μάθημα máthēma, "knowledge, study, learning") is the study of such topics as quantity, structure, space, and change.

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).

## Minute and second of arc

A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree.

## Natural science

Natural science is a branch of science concerned with the description, prediction, and understanding of natural phenomena, based on empirical evidence from observation and experimentation.

## Parsec

The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System.

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.

## Right ascension

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.

## Semi-major and semi-minor axes

In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the widest points of the perimeter.

## Solar System

The Solar SystemCapitalization of the name varies.

## Star

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.

## Telescope

A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).

## Trigonometry

Trigonometry (from Greek trigōnon, "triangle" and metron, "measure") is a branch of mathematics that studies relationships involving lengths and angles of triangles.

## Unit of measurement

A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity.

## References

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