Solar cycle 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 surfa ...

s are nearly periodic 11-year changes in the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

's activity that are based on the number of

sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...

s present on the Sun's surface. The first solar cycle conventionally is said to start in 1755 when

Rudolf Wolf Johann Rudolf Wolf (7 July 1816 – 6 December 1893) was a Swiss astronomer and mathematician best known for his research on sunspots. Wolf was born in Fällanden, near Zurich. He studied at the universities of Zurich, Vienna, and Berlin. Encke ...

began extensive reporting of sunspot activity. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. Sunspot counts exist since 1610 but the cycle numbering is not well defined during the Maunder minimum. It was proposed that one cycle might have been lost in the late 18th century, but this remains not fully confirmed. Solar cycles can be reconstructed indirectly, using the

radiocarbon Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

14C proxy, for the last millennium. The smoothing is done using the traditional SIDC smoothing algorithm. Using this algorithm, if the month in question is notated month 0, a weighted average is formed of months −6 to 6, where months −5 to 5 are given weightings of 1, and months −6 and 6 are given weightings of 0.5. Other smoothing formulas exist, and they usually give slightly different values for the amplitude and timings of the solar cycles. An example is the Meeus smoothing formula, with related solar cycles characteristics available in this STCE news item. The start of solar cycle 25 was declared by SIDC on September 15 2020 as being in December 2019. This makes cycle 24 the only "11-year solar cycle" to have lasted precisely 11 years.

Details of cycles 1 to 25

Unofficial cycles starting with a maximum

The following table is instead divided into (unofficial) cycles starting and ending with a maximum, to give a better feel for the number of spotless days associated with each minimum:

Comparison of cycles 24 and 25 by 13-month Running Averages

Following is a comparison of the growth of cycle 25 versus cycle 24, using the 13-month sunspot averages, beginning with the months of the respective minimums.
Numbers in brackets for cycle 25 indicate the minimum possible value for that month, assuming there are no more sunspots between now (Jan 13 2023) and six months after the end of the month in question.
The table shows averages for each hemisphere and the average for the entire Sun.

Comparison of Cycles 24 and 25 by Daily Spots

The following table gives the number of days so far in cycle 25 (to Jan 13 2023), and up to the same point in cycle 24 (to Jan 13 2012), which have passed various thresholds for the numbers of sunspots. As at Jan 13 2023, solar cycle 25 is averaging 11% more spots per day than solar cycle 24 at the same point in the cycle (Jan 13 2012).

References

External links

Solar Influences Data Analysis Center (SIDC)Graphics of historic solar cycles at the SIDC pageSORCE Total Solar Irradiance (TSI) Data
{{DEFAULTSORT:List Of Solar Cycles Periodic phenomena *