After all, the nearest star is just 93 million miles (150 million kilometers) away: the Sun. Its daily presence and predictable motions through the sky may make it seem like a boring, steady companion. But up close, it's an incendiary tempest of roiling plasma, erupting with brilliant solar flares and mottled by darker sunspots - not to mention it's the only star known (so far) to host a planetary system that includes an inhabited world.