Novas belong to the category of variable stars. Because of its sudden appearance, it was once considered as a newborn star, so it was named "new star".
Nova and supernova are a category of variable stars and an important link in the evolution of celestial bodies. It is the glorious funeral of old stars and the promoter of new stars. The explosion of supernovae may trigger the birth of countless stars in nearby nebulae. On the other hand, the ashes of nova and supernova explosions are also important materials for the formation of other celestial bodies. For example, many material elements on our planet today come from stars that have long since disappeared. Nova is a kind of cataclysmic variable star, which is a phenomenon of violent nuclear explosion caused by hydrogen accumulated on the surface of white dwarfs. This kind of star is usually very dark and difficult to find. When it broke out, it suddenly brightened and was considered a new star, hence its name. Novas is divided into fast nova (NA), medium nova (NAB), slow nova (NB) and extremely slow nova (NC) according to the speed of luminosity decline. During the explosion, the brightness will increase by tens of thousands, hundreds of thousands or even millions of times, lasting for several weeks or years. However, it should not be confused with Ia supernovae or explosions of other stars, including the glowing red nova first discovered by California Institute of Technology in May 2007.