Freda Van Natten, ago 11, of Howes Cave, N.Y., for her question:
Which is the biggest star in the sky?
The biggest stars are the red supergiants. One of the biggest is Antares, the big star at the heart of the summer constellation Scorpius, the Scorpion. This star is 390 times the diameter of our sun. If Antares were: to replace our sun, it would engulf Mercury, Earth and Venus and its outer rim would reach almost to the orbit of Mars.
Some stars vary in size, they swell up and shrink. One of these is the red supergiant Betelgeuse in the winter constellation of Orion, the Hunter. At its smallest, Big Bet is about 360 times the diameter of the sun, somewhat smaller than Antares. At other times, Betelgeuse swells up to 530 times the diameter of the sun.
If Betalguese were to replace our sun, there would be times when it swallow the inner planets, including Mars and its outer region would then come close enough to melt, the ice of Jupiter. There may be larger faraway stars not yet measured. But at its biggest, Betelguese is the biggest star we are likely to see in our sky.