A nova (latin: novus) means new. It means a new star. Actually it was already present but not visible to the naked eye, but when it exploded thousands of light years away and became thousands of time brighter, it become visible to the naked eye, even during the day. A dozen novas occur in the Milky way (Galaxy of our Earth) each year. The star explosively emits some of its mass as gas which is the reason for its brightness. This may be accompanied by radiation of dangerous...

 

electromagnetic waves. It then gradually cools down to become a white dwarf.

A supernova is the explosion of a much larger star, is much more destructive than a nova and a much rarer event. The Chinese recorded a supernova over 2000 years ago when it was visible during daylight for a period of 23 days. A supernova has to be within a distance of 30 light years of the earth for it to destroy the life in earth by its radiation. There is no other star except the sun within that range. To become a supernova within the next few million years, the sun itself will have to become supernova to destroy the Earth, which our scientists say the sun will never will.

A supernova could irradiate the earth with deadly cosmic radiation. Some scientists believe that the dinosaurs were wiped out due to such a phenomenon. A supernova is a giant explosion involving a star that is a dozen or more times as massive as the sun. These stellar explosions generate energy particles known as cosmic rays that can cause mutations in terrestrial organisms. They may cause leukaemia (cancer of blood forming tissue) in children and make their hair grey and fall off, like the hair in old people.