Solar flare. Computer artwork of a flare emerging from the Sun. A solar flare is an intense eruption of radiation and hot plasma (ionised gas) from the surface of the Sun. It can be many times the size of the Earth. It may result from a starquake, caused by shifts in the very strong magnetic fields of a star. If solar flare material impacts the Earth, or Earth's magnetosphere, it could disrupt radio communications and satellite operations. Solar flares also threaten astronauts working outside the protection of the Earth's atmosphere.