Astronomy Picture of the Day

Explanation: No supernova has ever been predicted. These dramatic stellar explosions that destroy stars and disperse elements that compose people and planets are not so well understood that astronomers can accurately predict when a star will explode - yet. Perhaps Sher 25 will be the first. Sher 25, designated by the arrow, is a blue supergiant star located just outside the star cluster and emission nebula NGC 3603. Sher 25 lies in the centre of an hourglass shaped nebula much like the one that surrounds the last bright supernova visible from Earth: SN1987a. Now the hourglass shaped rings around SN1987a were emitted before that blue supergiant exploded. Maybe Sher 25 has expelled these bipolar rings in a step that closely precedes a supernova. If so, Sher 25 may be within a few thousand years of its spectacular finale.