A nova is a powerful astronomical event that occurs in binary star systems, where two stars orbit each other. When one of the stars is a white dwarf, it can pull gas from its companion star. This gas accumulates on the surface of the white dwarf until a critical pressure and temperature are reached, leading to a sudden and dramatic increase in brightness. During a nova explosion, the star can brighten significantly, sometimes becoming thousands of times more luminous than before. This brightening can last for several days to weeks before the star gradually returns to its original state. Novae are different from supernovae, which are more energetic explosions marking the death of a star.