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Reference.org
Frame of reference
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<p>In <a href="/facts/Physics/a7aH2y08">physics</a> and <a href="/facts/Astronomy/0ArJVM1p">astronomy</a>, a frame of reference (or reference frame) is an abstract <a href="/facts/Coordinate_system/Mtd0q4SP">coordinate system</a>, whose <a href="/facts/Origin_(mathematics)/Lm26tRCB">origin</a>, <a href="/facts/Orientation_(geometry)/Tj24mTJ8">orientation</a>, and <a href="/facts/Scale_(geometry)/pFm6fvpu">scale</a> have been specified in <a href="/facts/Physical_space/tq6LUM3C">physical space</a>. It is based on a set of reference points, defined as <a href="/facts/Point_(geometry)/6YPAvX2a">geometric points</a> whose <a href="/facts/Position_(geometry)/Tpk5d9f2">position</a> is identified both mathematically (with numerical coordinate values) and physically (signaled by conventional markers). An important special case is that of <i><a href="/facts/Inertial_reference_frame/1U6TrdG3">inertial reference frames</a></i>, a stationary or uniformly moving frame. </p><p>For <i>n</i> dimensions, <i>n</i> + 1 reference points are sufficient to fully define a reference frame. Using <a href="/facts/Cartesian_coordinate_system/lkTqvMmB">rectangular Cartesian coordinates</a>, 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 <i>n</i> coordinate <a href="/facts/Cartesian_coordinate_system/lkTqvMmB">axes</a>. </p><p>In <a href="/facts/Theory_of_relativity/qGHj3eTC">Einsteinian relativity</a>, reference frames are used to specify the relationship between a moving <a href="/facts/Observer_(special_relativity)/t3yB2Bt9">observer</a> 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 <a href="/facts/Origin_(mathematics)/Lm26tRCB">origin</a>. A relativistic reference frame includes (or implies) the <a href="/facts/Coordinate_time/KcXozga6">coordinate time</a>, which does not equate across different reference frames <a href="/facts/Relative_motion/bVyzQ02h">moving relatively</a> to each other. The situation thus differs from <a href="/facts/Galilean_invariance/fFhMN2yv">Galilean relativity</a>, in which all possible coordinate times are essentially equivalent. </p>