Bradley la Brake, age 10, of Portland, Me., for his question:
What is a nova?
We do not need a telescope to spot a brilliant nova in the sky, and the word nova was coined before the telescope was invented. It means a new star, though we now know that it may be very old. It may appear new because we failed to notice it before it became a nova.
Aquilla, the eag1e, is a summer constellation between Sagittarius and the great square of Pegasus. Its only bright star is Altair, shining from the eag1e's shoulder. On the night of june 7, 1918, a new star appeared in Aquilla. Hour by hour it grew in brilliance and three nights later it outshone every other star in the sky. But its glory was short lived, for night by night it faded and later in September it became too dim to be seen without a telescope.
Telescope plates as a star too dim to be seen by human eyes. The nova outburst was a dramatic explosion during which its outer shells of blazing gases was hurled billions of miles into space. Astronomers kept detailed records and they estimate that the seething gases shot outward at from 600 to 1,000 miles a seoond. The dazzling light from these gases made the nova the brightest star in the sky.
Long after the explosion telescopes revealed a dim halo of expanding gases. Meantime the star shrank below the visible level and after six years it was back to its original size. The plural form of the word nova is novae and some novae are more showy and live longer than this one. But the show always is caused by exploding star material.
It is estimated that 20 to 30 stars in our galaxy become novae every year. At this rate, all our stars would become novae in 100,000 years but this is not likely. Certain stars seem more prone to explosions than others. Five years before the aquilla outburst, a nova appeared in the nearby constellation sagitta, the arrow. In 1946, 33 years later, this same star repeated its performance, step by step. Other stars have been observed to become novae three and even four times.
We are not sure what causes these explosions, but astronomers suspect that the inner core of certain stars are unbalanced. The balance is mot likely readjusted during the nova outburst. It may occur once in the lifetime of a star. But certain stars seem to need to burst off their outer shells again and again.
A nova is a brilliant display and at its peak it may outshine Sirius, the brightest star ever seen from the earth. But a nova is outshone by a supernova. This dazzling event is very rare and the trailing gases from the super explosion may be visible hundreds of years after the event. Astronomers suspect that in a supernova, all or most of the star's blazing material explodes into space.