LT spectra confirm nature of naked-eye Nova
A nova is a sudden brightening of a star, and they are thought to occur on the surface of white dwarf stars within a binary star system - i.e. a system with two stars. When the two stars are close to each other, the gravity of the white dwarf can pull material (mostly hydrogen) from the companion star. As the material starts to build up on the white dwarf, it's pressure and temperature starts to rise to a point where it ignites a runaway nuclear fusion reaction. This releases an enormous amount of energy that blows the remaining gases away and produces an extremely bright outburst of light. Typically, the brightness of the system will increase by a factor of 50,000 - 100,000 and decay slowly over the course of the next 25 - 80 days.