At a distance of 640 light years from Earth, recent announcements that Orion's second brightest star was about to go supernova would mean that the red giant would have had to have exploded in the middle ages.

According to Dr. Brad Carter, Senior Lecturer of Physics at Southern Queensland University:

"This old star is running out of fuel in its center. This fuel keeps Betelgeuse shining and supported. When this fuel runs out the star will literally collapse in upon itself and it will do so very quickly."

"It goes bang, it explodes, it lights up -- we’ll have incredible brightness for a brief period of time for a couple of weeks and then over the coming months it begins to fade and then eventually it will be very hard to see at all."

However, astronomers have since moved to allay concerns over when Betelgeuse may explode and to what effect after various exaggerated reports were picked up by media.

Firstly, it is pointed out that a supernova would have to be at a distance of no farther than 25 light years in order to affect the Earth. Secondly, there is no accurate way to predict when it may explode and thirdly, contrary to some claims, it would not appear anywhere near the brightness of the Sun. As Phil Plait from Discovery News explains: 

"At that distance, it’ll get bright, about as bright as the full Moon..It’ll hurt your eyes to look at it, but that’s about it..It won’t even get 1/100,000th that bright [as the Sun]."

All told, University of Illinois astronomer Jim Kaler summed things up quite nicely when asked what would be the effect of Betelgeuse exploding, when he replied:

"Well, it will make a God-awful mess of the constellation Orion."