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The Wolf number (also known as the relative sunspot number or Zürich number) is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the Sun. Historically, it was only possible to detect sunspots on the far side of the Sun indirectly using helioseismology.
Sunspot number is correlated with the intensity of solar radiation over ... This is a difference in total solar irradiance at Earth over the sunspot cycle of close ...
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.
Solar activity has been on a declining trend since the 1960s, as indicated by solar cycles 19–24, in which the maximum number of sunspots were 201, 111, 165, 159, 121 and 82, respectively. [14] In the three decades following 1978, the combination of solar and volcanic activity is estimated to have had a slight cooling influence. [ 15 ]
Sunspot activity has been measured using the Wolf number for about 300 years. This index (also known as the Zürich number) uses both the number of sunspots and the number of sunspot groups to compensate for measurement variations. A 2003 study found that sunspots had been more frequent since the 1940s than in the previous 1150 years. [30]
Solar maximum is typically associated with an increase in the number of sunspots visible on the sun’s surface. These dark regions, some of which can reach the size of Earth or larger, are driven ...
CMEs often form around sunspots, although scientists aren’t entirely sure why. Sunspot formation is cyclical, and the current solar cycle has reached the highest number of sunspots since 2001 ...
A sunspot this large is easy enough to see from Earth; all that is needed is a solar filter or pair of eclipse glasses to protect your eyes from the sun's dangerous rays. Sunspot AR3664 compared ...