"Clearly visible" means it can be seen with the naked eye at night and is large enough to be easily located without any special tools.
Be aware that this market is about whether a supernova CAN BE SEEN from Earth before 2100 (by a conscious self-aware entity), not about a supernova occurring within visible range. For example, space debris, future mega-structures, or climate conditions that make it very difficult or impossible to see a supernova even if it happens will not cause this market to resolve to YES.
This is a very long-term market, especially if you bet NO. Unless future technology extends life expectancy, chances are you won't see the outcome. Take that into account. Bet for your grandchildren?
There is a very slim chance that the Betelgeuse star has already gone supernova and we might get to see it this century. Other stars that we are not aware of could have gone supernova and become visible this century, but it is less likely that this market will resolve to YES as they may be too far away to be visible with the naked eye from Earth.
Resolves YES:
A supernova (star origin) is easily visible from Earth with the naked eye.
It must be reported by news and scientists as an actual supernova.
At least one conscious self-aware entity sees the supernova from Earth.
Resolves NO:
It is the year 2100 and the YES criteria have not been met.
Earth is destroyed or no longer has a conscious self-aware species (whether it is humans, AI, or otherwise) living there able to observe the phenomenon.
OP Trading: Given the objective nature of this market’s resolution, I reserve the right to place bets. However, I will do so only after at least 5 trades or trade orders from different traders have been made, to avoid any unfair advantage.