The word nova means "new star." Ancient civilizations interpreted these events as the creation of a new star. Novae (plural of nova) are actually explosions that occur on stars near the end of their lives.

In a binary system, a system in which two stars closely orbit each other, one star may influence the other. If the binary system consists of a white dwarf and a main-sequence star, gas may be pulled from the main-sequence star to the white dwarf. This is like dumping lighter fluid onto hot coals; the surface of the white dwarf explodes. Depending on how energetic the explosion is, the novae will fade away in a few days to a few weeks.

In the images below, you can see a nova appearing and fading.

For more information about novae, check out these sites: