orion betelguese nova
© WikipediaOrion on the Celestial Equator, with Betelgeuse highlighted
Since about October 2019, Betelgeuse (the bright reddish star at Orion's shoulder in the brightest constellation in the sky that is about 600 - 700 ly distant from us) has begun a sharp dimming that has now gone beyond what has been seen in modern observations. As of the end of January, it was down about 2.5 in apparent magnitude.

Here is its "portrait" — it is one of the few stars we have seen as a disk:
betelgeuse
A view of Betelgeuse from the ALMA observatory
Betelgeuse, captured by ALMA. Notice it is lop sided and seems to be roiled by large convection cells. In size, it is almost as large across as the orbit of Jupiter. As it is a red giant, it is thought to be end of life, and is due for supernova within the next 100,000 years.

As, normally we only see a supernova after it has happened, we do not know what precursors look like.

Some concerns have been expressed, that we may suffer x-ray bursts should that happen, but those tend to be aligned with the polar axis and such is thought to be unlikely. If it does go supernova, it will blaze up to high brightness, reaching that of the full moon approximately, then will fade away leaving behind a neutron star (or possibly a black hole, it seems to be borderline).

Here is a recent video:


This is a reminder that we are observing, we do not know to certainty.