The Frequency of Such Explosions.

Until recently, bright Novae were believed to be very rare, but five have already appeared since the beginning of the twentieth century. The last three were Nova Cygni 1920, Nova Pictoris 1925, and Nova Herculis 1934.

It has been estimated that, if the whole heavens could be photographed each night, at least twenty Novae would be discovered in our Galaxy every year, whilst many more might be found in the nearer Spiral Nebulae. It is very significant that in the great Nebula in Andromeda, which appears to be a younger and more condensed galaxy, Novae are about twice as numerous as in ours, but in that in the Triangle, in which the stars are widely scattered in long spiral arms, Novae are comparatively rare.