A nova is a powerful astronomical event that occurs in binary star systems, where one star is a white dwarf. When the white dwarf pulls in gas from its companion star, the accumulated material can ignite in a thermonuclear explosion on its surface. This explosion causes the star to suddenly brighten, sometimes becoming thousands of times more luminous than before. Novae are different from supernovae, which are more massive explosions marking the death of a star. The brightness of a nova can last for several weeks to months before gradually fading. Observing novae helps astronomers understand stellar evolution and the dynamics of binary systems.