Superflare
Since superflares can occur on stars apparently equivalent in every way to the Sun, it is natural to ask if they can occur on the Sun itself. An estimate based on the original Kepler photometric studies suggested a frequency on solar-type stars (early G-type and rotation period more than 10 days) of once every 800 years for an energy of 10 erg and every 5000 years at 10 erg. One-minute sampling provided statistics for less energetic flares and gave a frequency of one flare of energy 10 erg every 5–600 years for a star rotating as slowly as the Sun; this would be rated as X100 on the solar flare scale. This is based on a straightforward comparison of the number of stars studied with the number of flares observed. An extrapolation of the empirical statistics for solar flares to an energy of 10 erg suggests a frequency of one in 10,000 years.
Superflare
Superflare stars show a quasi-periodic brightness variation, which is interpreted as evidence of starspots carried around by solar rotation. This allows an estimate of the rotation period of the star; values range from less than one day up to tens of days (the value for the Sun is 25 days). On the Sun, radiometer monitoring from satellites shows that large sunspots can reduce the brightness by up to 0.2%. In superflare stars the most common brightness variations are 1-2%, though they can be as great as 7-8%, suggesting that the area of the starspots can be very much larger than anything found on the Sun. In some cases the brightness variations can be modelled by only one or two large starspots, though not all cases are so simple. The starspots could be groups of smaller spots or single giant spots.