SPECIAL RELATIVITY THEORY

The special theory of relativity was proposed in 1905 by Albert Einstein in his article "On the Electrodynamics of Moving Bodies." Some three centuries earlier, Galileo's principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest; a person on the deck of a ship may be at rest in his opinion, but someone observing from the shore would say that he was moving. Einstein's theory combines Galilean relativity with the postulate that all observers will always measure the speed of light to be the same no matter what their state of uniform linear motion is.
This theory has a variety of surprising consequences that seem to violate common sense, but which have been verified experimentally. Special relativity overthrows Newtonian notions of absolute space and time by stating that distance and time depend on the observer, and that time and space are perceived differently, depending on the observer. It yields the equivalence of matter and energy, as expressed in the famous equation E=mc2, where c is the speed of light. Special relativity agrees with Newtonian mechanics in their common realm of applicability, in experiments in which all velocities are small compared to the speed of light.
The theory was called "special" because it applies the principle of relativity only to inertial frames. Einstein developed general relativity to apply the principle generally, that is, to any frame, and that theory includes the effects of gravity. Special relativity doesn't account for gravity, but it can deal with accelerations.
Although special relativity makes relative some quantities, such as time, that we would have imagined to be absolute based on everyday experience, it also makes absolute some others that we would have thought were relative. In particular, it states that the speed of light is the same for all observers, even if they are in motion relative to one another. Special relativity reveals that c is not just the velocity of a certain phenomenon -- light -- but rather a fundamental feature of the way space and time are tied together. In particular, special relativity states that it is impossible for any material object to travel as fast as light.

ABOUT THE SUPERNOVA

A supernova is a stellar explosion that produces an extremely bright object made of plasma that declines to invisibility over weeks or months. There are several different types of supernovae and two possible routes to their formation. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core and collapse inward under the force of its own gravity to form a neutron star or black hole, or a white dwarf star may accumulate material from a companion star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, completely disrupting it (note that this should not be confused with a surface thermonuclear explosion on a white dwarf called a nova). In either case, the resulting supernova explosion expels much or all of the stellar material with great force.
The explosion drives a blast wave into the surrounding space, forming a supernova remnant. One famous example of this process is the remnant of SN 1604, shown to the right.
"Nova" (pl. novae) is Latin for "new", referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super" distinguishes this from an ordinary nova, which also involves a star increasing in brightness, though to a lesser extent and through a different mechanism. However, it is misleading to consider a supernova as a new star, because it really represents the death of a star (or at least its radical transformation into something else).