Apparently Sirius, hands down the brightest star in the sky, was blood red in antiquity but blazes blue-white today, just 1500 years later. The evidence is compelling. The problem is, no known astrophysical process can account for the change. Read all about it here, and go here for more discussion.
By the way, I love it when stuff like this comes along. It doesn’t mean that science is wrong or that science doesn’t work. It means that there is plenty of stuff that we haven’t figured out, and some of it is, like, huge. As someone who loves figuring stuff out, I take a lot of comfort from that. I want some of that pie for myself. But in this area, at least, I can also get some satisfaction just from looking at other people’s plates.
How wonderful that we have met with a paradox. Now we have some hope of making progress. ~Niels Bohr