The roughly 11-year cycle of variation of the number of sunspots visible on the sun.

(or solar cycle): an irregular cycle, averaging about 11 years in length, during which the number of sunspots (and of their associated outbursts) rises and then drops again. Like the sunspots, the cycle is probably magnetic in nature, and the polar magnetic field of the Sun also reverses each solar cycle.

The semiregular 11-year period with which the frequency of sunspots fluctuates.

Periodic variation in the number of sunspots which is related to changes in overall solar activity. The period of the cycle is 10 - 11 years. At the beginning of the cycle there are few, if any, sunspots, but numbers increase as time goes by, then decrease once maximum has passed. This cycle seems to be caused by the interaction between the 'dynamo' which generates the Sun's magnetic field and the Sun's rotation.

A cycle of variation in the total number and area of spots on the sun's surface, from a maximum to a minimum with an average period of 11 years. Since magnetic fields on the sun reverse with each such cycle, the period of a complete cycle of spottedness-plus-magnetic-condition is 22 years.

The recurring, eleven-year rise and fall in the number of sunspots.

The cyclic appearance of large numbers of sunspots (black spots thought to be magnetic storms on the Sun's surface) every 9 to 11.5 years.

a cycle averaging 11 years in which the number of sunspots increases and decreases.

A cycle with an average length of 11.1 years, but varying between about 7 and 17 years.

The regular increase and decrease in the number of sunspots over the course of roughly 11 years; see also "solar cycle."

cycle with an approximate length of 11 years, but varying between about 7 and 17 years, in the number and area of sunspots, as given by the relative sunspot number. This number rises from a minimum of 0â€“10 to a maximum of 50â€“140 in about four years time, and then declines more slowly. An approximate 11-year cycle has been found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics. The u index of geomagnetic intensity variation shows one of the strongest known correlations to solar activity. See also solar cycle.

The change in strength of the Sun's magnetic field, which determines the number of sunspots and the amount of particles emitted in the solar wind. The period of the cycle is about 11 years.