A sequence of changes that happens over and over again is cyclical. The extent of variation during a cycle can disrupt the system. Things change with time in different ways, such as in size, weight, color, and movement. Some small changes can be detected by taking measurements. Often the best way to tell which kinds of change are happening is to make a table or graph of measurements.
Different cycles range from thousands of years down to less than a billionth of a second.
Ulysses discovers that high speed solar wind streams seen during solar minimum in 1994 over the south pole, are absent during solar maximum conditions in 2000. Ulysses, Voyager, and IMP-8 discover that solar wind pressure changes during the solar activity cycle occur at all solar lattitudes. Yohkoh satellite observes a global change in the Sun's magnetic field during a sunspot cycle.