The novae, or "new" stars

    A fascinating class of intrinsic variables are the exploding stars known as novae, or new stars. They were given that name because to the older astronomers they ap­peared to be newly created. We realize now, however, that a nova is not "new"; it is a pre-existing star upon which an ex­plosion has taken place.
    A faint star, perhaps too faint to be seen by any except the most powerful telescopes, begins to be more brilliant. Within the space of a few days it becomes thou-sands of times brighter than it was before. After some days of maximum brilliance, the luminosity begins to fade. Ultimately, the star is about as faint as it was before. This would seem to indícate that the outburst is far more superficial than it would appear to be. The explosion of novae occurs without warning. On the average, they increase about 60,000 times in bright­ness, corresponding to thirteen magnitudes. Always the growth of brilliance in a nova is extremely rapid and its fading is gradual.
    A nova is designated by the word "Nova," followed by the genitive (possessive form) of the constellation in which it occurs and the year in which the outburst took place. For example, when we refer to Nova Persei 1901, we have in mind the nova that appeared in the constellation Perseus in the year 1901.