Outside the solar disk cool emissions can be recorded. They are inserted into the surrounding hot corona and their properties are still not well known. Emissions from neutral hydrogen can be registred using the well known H-alpha line. With a coronagraph it is possible to record this line through an interference filter broad enough to avoid Doppler effects. In these observations we used a 0.3 nm width filter associated to a 15 cm aperture coronagraph equipped with a 16 bits 1K-CCD camera. The filter is wide enough to excude all usual Doppler shift effects produced during a prominence eruption.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html