Why can solar prominences appear dark against the Sun but bright against the sky?

Solar prominences are clouds of plasma supported by magnetic fields above the Sun's surface. Their appearance depends on the contrast between the prominence and the background against which it is viewed.1

Prominences absorb radiation from the solar layers below them and re-emit it in all directions through a process known as pure scattering. When a prominence is positioned in front of the Sun's bright disk, the light that would have reached an observer is removed from the upward beam, causing the prominence to appear as a dark feature, historically referred to as a filament.12

Conversely, when a prominence is viewed against the sky at the Sun's limb, it appears bright because the sky behind it is significantly darker than the prominence itself. In this orientation, the scattered light from the prominence is easily visible against the dark backdrop of space.1