heat lightning: bright flashes of light near the horizon without thunder (especially on hot evenings); usually attributed to distant lightning that is reflected by clouds
lightning: the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more
harp: a chordophone that has a triangular frame consisting of a sounding board and a pillar and a curved neck; the strings stretched between the neck and the soundbox are plucked with the fingers