A supernova explosion can be caused in several different ways, but the most common is when the core of a star collapses. This happened due to the immense force that gravity is imposing on the mass of the star causing the star to be focused on a single point and exploding out faster than the speed of light. Stars can go supernova at any moment and our own planet, Earth, can feel the side effects of such an explosion.

If our sun decided to go supernova at any moment it would be like a 1,000 nuclear bombs hitting the earth every second. Supernova explosions can be looked at like waves. We think of explosions as an instantaneous outburst in energy, but a supernova is like a volcano exploded and a tsunami following up right after that. These explosions can last for thousands of years, with the explosion pushing nearby gas at the speed of light creating a trail of destruction until the materials of the supernova cools down and is directed back into the universe. There are several different ways our planet could come in contact with a supernova. The real damage occurs once a supernova is within 300 light years away from Earth. 

The most dangerous of these distances is four light years away and closer. Though, it is extremely unlikely for a supernova to explode this close to us, if it were to happen, the earth would be completely toast. Being able  to cast two shadows for a couple hours would be fun, but soon after the surface of the earth would be as hot as a sauna, completely scorching the earth, killing off all major life on earth. The ozone layer would be completely toast on top of this, letting in all of the toxic, radioactive waves to shower the Earth. This would kill everything outside of the deep-sea dwellers and insects that live in the soil. Life on Earth would have to restart entirely.

Supernovas are just one of  several things that make space a scary place, but they are not something to fear. Space is so vast that the chances of a supernova happening that close is highly unlikely. The best part about it, is that supernovas have even helped us with protecting us from other possible supernovas from happening close to us. It is believed that a supernova exploded near earth, causing the extinction of the Devonian period. This supernova pushed all the gasses away from earth, creating a cloud around our solar system that is now a hot pot for star creation.