The Sun is starting to wake up from a long and quiet slumber. Dark sunspots are breaking out on its surface, and big eruptions of gas and energy are streaming through the solar system. And as the Sun rouses itself even more, we'll see powerful explosions known as solar flares.

Even the biggest solar flares are small compared to one that rocked a star in Bootes almost two decades ago.

Beta Bootis is a stellar giant -- about 20 times wider than the Sun -- an indication that it's nearing the end of its life.

Giants don't often produce big flares because they don't spin very fast. Flares and sunspots are produced by a star's magnetic field, which is generated by different layers of gas rotating at different speeds. The faster a star spins, the more powerful its magnetic field.

In 1993, though, an orbiting telescope detected a huge blast of X-rays from Beta Bootis. The source was a flare that was more powerful than even the biggest flares on the Sun. If any planets orbit the star, they received a massive dose of X-rays. And if they have atmospheres, they would have seen brilliant aurorae -- the shimmering curtains of light in the night sky.

Astronomers haven't detected any repeat outbursts from Beta Bootis. But its flare-up suggests that giant stars may not be quite so quiet after all.

Bootes is high in the sky at nightfall. It looks like a faint kite, with brilliant Arcturus at the tail. Beta Bootis is at the top of the kite, far to the left of Arcturus.