Seen from overhead, filaments appear as dark, thread-like features across the sun's surface. They consist of searingly hot gas that nevertheless is cooler than the surface. Seen broadside, however, they form a visible arch above the sun's surface, known as a solar prominence. The arc traces a looping magnetic field the electrically charged gas follows. Filaments are thought to be one source for coronal-mass ejections, vast, high-speed clouds of charged particles that filaments can release in crack-the-whip-like fashion if one end of the magnetic loop looses its grip. The coronal-mass ejections from filaments tend to be relatively weak.