Betelgeuse is so big that if it replaced the Sun it would swallow the planets out to Jupiter

The Sun is enormous — over a million Earths would fit inside it. But the Sun is a perfectly ordinary star, and some are so vast they make it look like a marble. Betelgeuse, the orange-red shoulder of the constellation Orion, is a red supergiant with a radius roughly 700 times that of the Sun.

That number is hard to feel until you place it in our own solar system. If Betelgeuse swapped in for the Sun, its glowing surface wouldn’t stop at Mercury, or Earth, or even Mars. According to NASA, the star would stretch past Jupiter’s orbit — a single object swallowing the planets out to the largest world in the solar system, asteroid belt and all.

Mercury, Venus, Earth, Mars: all of us, deep inside one star.

Betelgeuse is so distended because it is dying. Having burned through the hydrogen in its core, it has bloated outward, its outer layers spread thin and cool. Despite that vast size it holds only around 15 times the Sun’s mass, making it astonishingly tenuous — closer to a hot vacuum than to anything solid.

Its exact diameter is genuinely hard to pin down: the star pulsates and its hazy edge shifts, so estimates wander by hundreds of solar radii. Either way, it is colossal — and astronomers expect it to end in a brilliant supernova.