Solar cycle

This article is about the sunspot cycle. For the 28-year cycle of the calendar, see Solar cycle (calendar).

Line graph showing historical sunspot number count, Maunder and Dalton minima, and the Modern Maximum
400 year sunspot history, including the Maunder Minimum
"The prediction for solar cycle 24 gave a smoothed sunspot number maximum of about 69 in the late Summer of 2013. The smoothed sunspot number reached 68.9 in August 2013 so the official maximum was at least that high. The smoothed sunspot number rose again towards this second peak over the last five months of 2016 and surpassed the level of the first peak (66.9 in February 2012). Many cycles are double peaked but this is the first in which the second peak in sunspot number was larger than the first. This was over five years into cycle 24. The predicted and observed size made this the smallest sunspot cycle since cycle 14 which had a maximum of 64.2 in February of 1906."[1]

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 Sun's surface. Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and size of sunspots, solar flares, and coronal loops all exhibit a synchronized fluctuation from a period of minimum activity to a period of a maximum activity back to a period of minimum activity.

The magnetic field of the Sun flips during each solar cycle, with the flip occurring when the solar cycle is near its maximum. After two solar cycles, the Sun's magnetic field returns to its original state, completing what is known as a Hale cycle.

This cycle has been observed for centuries by changes in the Sun's appearance and by terrestrial phenomena such as aurora but was not clearly identified until 1843. Solar activity, driven by both the solar cycle and transient aperiodic processes, governs the environment of interplanetary space by creating space weather and impacting space- and ground-based technologies as well as the Earth's atmosphere and also possibly climate fluctuations on scales of centuries and longer.

Understanding and predicting the solar cycle remains one of the grand challenges in astrophysics with major ramifications for space science and the understanding of magnetohydrodynamic phenomena elsewhere in the universe.

The current scientific consensus on climate change is that solar variations only play a marginal role in driving global climate change,[2] since the measured magnitude of recent solar variation is much smaller than the forcing due to greenhouse gases.[3]

Evolution of magnetism on the Sun
  1. ^ "NASA/Marshall Solar Physics". nasa.gov. Retrieved 2015-11-17. Public Domain This article incorporates text from this source, which is in the public domain.[dead link]
  2. ^ Cite error: The named reference haigh was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference grida fig6-6 was invoked but never defined (see the help page).