Could anything ever be brighter than the sun in our sky? Is there anything that could explode or exist that would appear brighter than the sun in our sky? There was that meteor in Russia in 2013 where it appears brighter than the sun. However, is there a possibility that something much further away from the sun could appear brighter than it for a short period of time? For example, could a star we can already see in our sky go supernova and appear brighter than the sun? I have been thinking about this for a while but don't have the skills to carry out any calculations.
If so, what is the furthest possible thing that we could see brighter than the sun. Another galaxy?
 A: There is a useful rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they're bigger than that.
Disproving the rule, a quick search suggests that our most probable next nearby supernova would be about as bright as the full Moon.
However,

It turned out to be fortunate that [gamma ray bursts] were so far away. “If there was a gamma-ray burst in our galaxy with a jet pointed at us, the best thing you could hope for is a quick extinction,” said Zhu. “You would hope that the radiation smashes through the ozone and immediately fries everything to death. Because the worst scenario is if it’s farther away, it could cause some of the nitrogen and oxygen in the atmosphere to turn into nitrous dioxide. The atmosphere would turn brown. It would be a slow death.”

A: An atomic bomb or a hydrogen bomb blast will be many, many times brighter than the sun if you are standing close enough to it when it goes off. Note that the sun's rays are insufficient to burn you to a cinder in an instant, but the radiation from one of those bombs can readily do this to you.
