The 10th brightest star, Betelgeuse, marking Orion’s shoulder, started dimming dramatically in 2019. Less than 10 million years old, the red star has evolved rapidly and was expected to end its evolution with a supernova explosion, most likely within 100,000 years. However, scientists refute this claim.
Observations by NASA's Hubble telescope show that the dimming was caused by super hot plasma ejected by the star's surface into space. Researchers could see its effect in the southeast part of the star and measured it moving about 200,000 miles per hour passing from the star's surface into its outer atmosphere. This material continued to travel beyond Betelgeuse's visible surface, reaching millions of miles from the seething star. At that distance, the material cooled down enough to form dust, thus blocking the starlight from Beteleguese's surface and making it look dim.
The star is relatively nearby, about 725 light-years away, which means the dimming would have happened around the year 1300. But its light is just reaching Earth now.
Although if and when Betelgeuse explodes, it will shine as bright as half-moon for more than 3 months. It will be visible in the daytime for roughly a year and in the nighttime for several years, as the supernova dims.