The biggest thing on the sun today is not a sunspot--and it's not even close. A dark magnetic filament 20 times wider than a typical sunspot is meandering across the sun's southern hemisphere. It's so big, astrophotographer Pete Lawrence of Selsey, UK, had to stitch together several pictures to display the entire structure:

Magnetic Filament on Sun
© Pete Lawrence
The filament is filled with relatively dense plasma held above the stellar surface by magnetic forces. Because this plasma is cooler than the sun below, it appears dark. In fact, it is not. If you could hold the filament out against the black of space, it would glow more brightly than a full Moon.

The 400,000-km scale of the filament--long enough to stretch from Earth to the Moon!--makes it an easy target for safely-filtered backyard optics. If you have a solar telescope, take a look.

More Images:

From Stephen Ramsden of Immaculate Heart of Mary Catholic School, Atlanta, GA; from Jean-Pierre Brahic of Uzès ( France); from Michael Boschat of Halifax,Nova Scotia,Canada; from James Kevin Ty of Manila , Philippines; from the Solar Dynamics Observatory in Earth orbit; from Didier Favre of Brétigny-sur-Orge, France; from Ron Cottrell of Oro Valley, Arizona.