Developed and published in 1905 by Albert Einstein, it deals with the measurement of physical quantities by observers who are in uniform motion with respect to each other

A theory postulated by Albert Einstein in 1905 that rejects the Newtonian notion of absolute space and time, based on the observation that the speed of light is independent of the motion of an observer. According to the theory, no matter what the speed of an observer, the speed of light will always measure 3 x 10^8 m/s, often abbreviated c. From this foundation, Einstein constructed a revolutionary model of gravity and was able to predict such surprising phenomena as black holes, gravity waves, time dilation, and the equivalence of mass and energy: E=Mc^2. Astronomers and astrophysicists regularly make use of the theoretical tools of special relativity to interpret and analyze light. For instance, astronomers rely on Doppler shift measurements to calculate the motions of stars and galaxies. The most distant galaxies show Doppler shifts which might imply that that they are moving faster than the speed of light. But using the proper formula from Special Relativity, instead of the simpler Newtonian equation, we find that the galaxies are speeding away from us at 90%, or 95%, or 99% the speed of light. See also General Theory of Relativity

A description of the relationships and interactions between moving objects. The 'special' theory only applies to the special case of objects moving at constant speeds in straight lines. It does not deal with accelerated motions.