Filament on the disk ... prominence at the limb...

 Chromospheric filaments, dark elongated features observed on solar disk in spectral lines such as H-alpha hydrogen line, become bright prominences, when viewed off the solar limb. Here an example of a filament turning prominence as observed by GONG station at Learmonth, Australia. Upper panel shows full disk images taken with H-alpha over several days. Low panels are a magnified view of a corresponding portion of solar disk.