INTEGRATED 24

Type I Supernova, the kind of supernova that you read about in the reading passage, is not the only kind of supernova. The other kind of supernova is called, as you might expect, a Type II supernova.

A Type II supernova occurs when a large star, a single star and not a double star, is in the process of dying. A Type II supernova occurs only in a star that is truly massive, a star that is at least ten times as massive as our Sun.

A supernova occurs in this type of massive star only when it is very old. The core of such a massive star in its very late stages of life becomes progressively hotter and hotter until the core collapses and a whole series of thermonuclear reactions occur, causing a supernova.

Probably the most famous and brightest historical Type II supernova occurred in 1054, near the beginning of the last millennium. It was recorded in China, and Chinese records indicate that it was visible to the naked eye even during daylight for twenty-three days and was visible to the naked eye at night for 653 days, or almost two years. The Chinese also recorded two other supernovae, in 1006 and in 1181, though these were not as bright as the 1054 supernova. From then, it was not until 1987 that another Type II supernova was visible to the naked eye. In 1987, a Type II supernova occurred in a galaxy close to the Milky Way, our galaxy. This was the only supernova that was strong enough and close enough to Earth to be seen from Earth without a telescope in over 400 years, since the two Type I supernovae were observed in 1572 and 1604. The 1987 supernova was the only Type II supernova to be visible to the naked eye in close to a thousand years.