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The Sun's photosphere is a plasma, an ionized gas made up of charged particles. The Sun also has a magnetic field. The field is tethered deep within the Sun, but field lines loop out into space. Occasionally eruptions of gas from the surface travel along the field lines. Excitation of the gas creates emission at visible wavelengths and even x-rays and also creates spectacular prominences. These transient features leaping out from the Sun's photosphere can be huge, several times the Earth's dimension, and they can come and go in timescales of only an hour. The largest blasts from active sunspot sites are called solar flares.
