Earth's sun is a predictable star, and that's a good thing: if the sun fluctuated in its brightness significantly from year-to-year, the solar system would be a much less hospitable place for life. But while most stars in the universe are as regular as our sun, a small percentage aren't — and when a star suddenly dims or brightens, it usually signifies something odd is happening with it, or even that it could be on the verge of exploding.
So when astronomers noticed in 2019 that Betelgeuse had dimmed, some speculated that the massive star was going to expand into a supernova so large it would be visible from Earth even during the daytime hours. Given that Betelgeuse is the tenth-brightest star in the night sky, citizens of Earth paid attention. Novas or supernovas that are visible with the naked eye are rare, and when they do happen, they tend to be generation-defining events: the last time a nearby star went supernova, in 1604, it was so bright that it was visible during the daytime.
