Regarding your previous answer about the Betel…

Regarding your previous answer about the Betelgeuse. In the gif you've posed the star seems to expand really quickly within seconds. Is that how it would really happen. Or would it take longer, days, weeks, etc? And for how long would the supernova be visible after the explosion?

A star (> 10 solar masses) will burn more and more heavy elements during its life to remain stable in the face of the force of gravity, until the production of iron begins, from there begins the end of a star. Iron, however, needs to absorb energy to merge into heavier elements. The formation of iron in the nucleus effectively completes the fusion processes and, without energy to support it against gravity, the star begins to collapse on itself. The star has less than 1 second remaining life. So the star explosion itself happens very fast.

But to be honest, I’m not sure what it would be like to see this explosion seen from Earth, I think the brightness of the supernova would increase with the passing of days (or not).

The time that would be visible in the sky would depend on the explosion, the distance, and other factors. A bright enough supernova could last for several months until it disappears slowly.

For example,

SN 1054 is a supernova that was first observed on 4 July 1054, and remained visible for around two years. 

SN 1006 supernova was a supernova that is probably the brightest stellar event observed in recorded history, reaching an estimated visual magnitude at -7.5, and exceeding approximately sixteen times the brightness of Venus. links: x, x, x, x, x