Red giants release most of their energy as infrared radiation, undetectable to human eyes. Betelgeuse is an M2 star (of luminosity class Iab), whereas Antares is M1.5. This would seem to suggest that Betelgeuse has a cooler surface. But experts say that there is probably not a strong correlation between surface temperature and spectral subtype among different M-type stars. The energy released by Betelgeuse is estimated to be only about 13 percent visible light. Depending on what percentage of Antares's output of electromagnetic radiation is visible, could it be that Betelgeuse produces more total radiation than Antares? The claim has long been made that if we were able to record all wavelengths of light with our eyes, Betelgeuse would appear brighter than any other star in the night sky—perhaps as bright as Venus now does.
But how bright will Betelgeuse get in visible light in our sky if it goes supernova?
Betelgeuse should go supernova sometime between now and a few million years hence. If it goes off early in this period, it should be close enough to us to burn brighter than the Full Moon in our sky. But perhaps we shouldn't hope for this show in our lifetime. For it also may damage and disturb Earth's biosphere at least slightly with a powerful dose of hard radiation.
Betelgeuse is the classic "red giant" star—a stage in stellar life that perhaps every star we see with the naked eye in our sky is either going through or will go through someday. Our Sun will probably never swell to more than about the diameter of the Earth's orbit and probably not for something like 5 billion years (though recent studies suggest that the Earth could become unlivable from the earlier phase of a swelling red Sun as "soon" as about 1 billion years from now). Our Sun is not massive enough to ever go supernova. But Betelgeuse is thought to have started its life with maybe as much as thirteen to seventeen times more mass than the Sun. The behemoth is unlikely to ever lose enough of its mass to stellar wind for it to avoid eventually going supernova.
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