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Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. [1]
Reconstruction of solar activity over 11,400 years. Sunspot numbers over the past 11,400 years have been reconstructed using carbon-14 and beryllium-10 isotope ratios. [10] The level of solar activity beginning in the 1940s is exceptional – the last period of similar magnitude occurred around 9,000 years ago (during the warm Boreal period).
The Wolf number sunspot index counts the average number of sunspots and groups of sunspots during specific intervals. The 11-year solar cycles are numbered sequentially, starting with the observations made in the 1750s. [29] George Ellery Hale first linked magnetic fields and sunspots in 1908. [30]
The 11-year activity cycle of the Sun is tied to the number of sunspots, which in turn are linked to the intensity of space weather, including solar flare activity from the star.
The Sun has reached a period of peak activity in an 11-year cycle known as the Solar Maximum, ... The past two years marked the active phase of the solar cycle with a higher number of sunspots.
Solar maximum is the regular period of greatest solar activity during the Sun's 11-year solar cycle. During solar maximum, large numbers of sunspots appear, and the solar irradiance output grows by about 0.07%. [2] On average, the solar cycle takes about 11 years to go from one solar maximum to the next, with duration observed varying from 9 to ...
The sun emits the largest solar flare of this 11-year cycle, as imaged by NASA's Solar Dynamics Observatory on October 3. NASA/SDO NASA says the sun is in the highly active "maximum phase" of its ...
The periodicity is not constant but varies roughly in the range 9.5 to 11 years. [4] The international sunspot number series extends back to 1700 with annual values while daily values exist only since 1818. Since 1 July 2015 a revised and updated international sunspot number series has been made available. [5]