The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the solar surface. Sunspots have been observed since the early 17th century and the sunspot time series is the longest continuously observed (recorded) time …

The solar mass (M ☉) is a standard unit of mass in astronomy, equal to approximately 2 × 10 30 kg.It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes.It is approximately equal to the mass of the Sun.This equates to about two nonillion (short scale) or two quintillion () kilograms: . M ☉ = (1.988 47 ± 0.000 07) × 10 30 kg