Hα image of the prominence at the west limb, 52° north, from June 6, 2022, (GONG archive); North direction is upward; the long lines mark the direction of refraction at two slit positions beside the prominence used for the determination of parasitic light; the short lines mark slit positions reconstructed from the observed Hγ intensity variation and their extension of 12″ corresponds to 8.7 Mm.