Betelgeuse is a red supergiant star in the constellation Orion. It is about 724 lightyears away from Earth, and it has a mass of about 11 times that of the Sun. Despite that, it is about 700 times larger. If it were at the center of our solar system, it would engulf the four inner planets and Jupiter.

It's so big because it is currently reaching the end of its life. Massive stars have dramatically shorter lifespans than stars like the Sun because the rate of nuclear fusion in their cores is accelerated due to the massive gravitational pressures. This accelerated rate of fusion is producing huge outward pressures, puffing the star up to many, many times its original size. Once Betelgeuse runs out of fusible elements, that pressure will suddenly disappear and gravity will cause the star to implode, releasing ridiculous amounts of energy in a supernova.

Betelgeuse only formed about ten million years ago and is already on death's door. Astronomers don't know enough about stellar evolution to predict exactly when Betelgeuse will go supernova. But from what they do know, they're saying it could go off anytime between right now and the next 100,000 years. Since it is 724 lightyears away, we won't know until 724 years after the fact. So if we're lucky, we'll get to see the supernova if it already exploded about that long ago!

The last time a supernova was visible to the naked eye was in 1604. Today it's called Kepler's Supernova, named for Johannes Kepler, one of the astronomers who observed it at the time. The supernova was about 20,000 lightyears away and was bright enough to be visible during the day for three weeks.

Recently, astrophysicists have determined that saying the word Betelgeuse three times may cause it to explode sooner than it would have otherwise.

https://astronomy.com/news/2020/02/when-betelgeuse-goes-supernova-what-will-it-look-like-from-earth