The distance of a supernova candidate from Earth can vary greatly, but on average, they are located thousands of light-years away. The closest supernova ever recorded was SN 1987A, which was about 168,000 light-years away from Earth.
While a supernova is a powerful and destructive event, it is unlikely to directly harm Earth. The closest supernova to Earth in recorded history occurred in 1006 AD and did not cause any noticeable effects on our planet. However, if a supernova were to occur within 50 light-years of Earth, it could potentially have damaging effects on our ozone layer.
Scientists constantly monitor the night sky for potential supernova candidates and have systems in place to alert us if one is detected. In the event of a nearby supernova, the best course of action would be to seek shelter in a sturdy building to protect from any possible radiation or debris.
Currently, there is no way to accurately predict when and where a supernova will occur. However, scientists are able to identify potential supernova candidates by studying the life cycle of massive stars and monitoring the night sky for any changes or anomalies.
The farther away a supernova candidate is from Earth, the less likely it is to pose a danger to our planet. The energy and radiation from a supernova dissipate over distance, so the farther away it is, the less impact it will have on Earth. However, a supernova within a few hundred light-years could potentially have a more significant impact on our planet.