Editing Frame of reference (section)

{{short description|Abstract coordinate system}}
{{Other uses|Frame of reference (disambiguation)}}
{{Classical mechanics |Fundamentals}}

In [[physics]] and [[astronomy]], a '''frame of reference''' (or '''reference frame''') is an abstract [[coordinate system]], whose [[origin (mathematics)|origin]], [[orientation (geometry)|orientation]], and [[scale (geometry)|scale]] have been specified in [[physical space]]. It is based on a set of '''reference points''', defined as [[point (geometry)|geometric points]] whose [[position (geometry)|position]] is identified both mathematically (with numerical coordinate values) and physically (signaled by conventional markers).<ref name="Kovalevsky Mueller 1989 pp. 1–12">{{cite book | last1=Kovalevsky | first1=J. | last2=Mueller |author-link=Jean Kovalevsky |first2=Ivan I. |author-link2=Ivan I. Mueller |title=Reference Frames | chapter=Introduction | series=Astrophysics and Space Science Library | publisher=Springer Netherlands | publication-place=Dordrecht | year=1989 | volume=154 | issn=0067-0057 | doi=10.1007/978-94-009-0933-5_1 | pages=1–12| isbn=978-94-010-6909-0 }}</ref>
An important special case is that of ''[[inertial reference frame]]s'', a stationary or uniformly moving frame.

For ''n'' dimensions, {{nowrap|''n'' + 1}} reference points are sufficient to fully define a reference frame. Using [[Cartesian coordinate system|rectangular Cartesian coordinates]], a reference frame may be defined with a reference point at the origin and a reference point at one unit distance along each of the ''n'' coordinate [[Cartesian coordinate system|axes]].{{Citation needed|date=December 2020}}

In [[Theory of relativity|Einsteinian relativity]], reference frames are used to specify the relationship between a moving [[Observer (special relativity)|observer]] and the phenomenon under observation. In this context, the term often becomes '''observational frame of reference''' (or '''observational reference frame'''), which implies that the observer is at rest in the frame, although not necessarily located at its [[origin (mathematics)|origin]]. A relativistic reference frame includes (or implies) the [[coordinate time]], which does not equate across different reference frames [[relative motion|moving relatively]] to each other. The situation thus differs from [[Galilean invariance|Galilean relativity]], in which all possible coordinate times are essentially equivalent.{{Citation needed|date=December 2020}}