## charge-coupled device

Overview page. Subjects: Astronomy and Astrophysics — Computing.

(CCD)

A light-sensitive semiconductor used to enhance images obtained from faint objects. It accumulates and temporarily stores charge at particular pixel locations when struck by...

## Coordinated Universal Time

Overview page. Subjects: Astronomy and Astrophysics — Computing.

An international standard which defines the time throughout the world. Signals which send coordinated universal time values are broadcast regularly from land transmitters and satellites...

## curvature

Overview page. Subjects: Mathematics — Astronomy and Astrophysics.

The rate of change of direction of a curve at a point on the curve. The Greek letter *κ* is used to denote curvature and

*ρ*= 1 κ is the radius of curvature which is the...

## figure

Overview page. Subjects: Astronomy and Astrophysics — Mathematics.

The shape given to an optical surface during manufacture. The process of producing or altering the shape is known as figuring.

## front-end processor

Overview page. Subjects: Computing — Astronomy and Astrophysics.

An I/O processor that is used to format and/or process input data. The term is sometimes used to refer to a communication processor. Compare back-end processor.

## gravitational mass

Overview page. Subjects: Astronomy and Astrophysics — Mathematics.

A measure of the quantity of matter in a body. It is measured in kilograms. Mass determines the strength of the gravitational force exerted by an object. *See also* inertial mass.

## inertial mass

Overview page. Subjects: Mathematics — Astronomy and Astrophysics.

A measure of a body's resistance to a change in its velocity or state of rest. Inertia is a direct property of the mass of a body: the greater the mass, the greater its inertia. Although...

## International Atomic Time

Overview page. Subjects: Astronomy and Astrophysics — Computing.

The most accurate time that is available to computers in a distributed system. Clocks which adhere to this standard are accurate to one part in 10,000,000,000,000. Such clocks are often...

## light year

Overview page. Subjects: Mathematics — Astronomy and Astrophysics.

(l.y.) The distance travelled by light, or other electromagnetic radiation, in one tropical year through space. One light year equals 9.4605 × 10^{12} km, or 63240 astronomical units, or...

## metric

Overview page. Subjects: Mathematics — Astronomy and Astrophysics.

The function *d* used to define a distance between two points in constructing a metric space, with the following properties:

*d*(*x*, *y*)=0 if and only if *x*=*y*,

null...

## pincushion distortion

Overview page. Subjects: Astronomy and Astrophysics — Computing.

An optical defect in which the magnification of a lens decreases with distance from the optical axis, giving the image of a square object with concave sides, like a pincushion.

## redundancy

Overview page. Subjects: Computing — Astronomy and Astrophysics.

The provision of additional components in a system, over and above the minimum set of components needed to perform the functions of the system, for purposes of reliability or robustness....