  The so-called solar cycle is generally characterized by the quasi-periodic
oscillatory evolution of the photospheric spots number. This quasi-periodic
pattern has always been an intriguing question. Several physical models were
proposed to explain this evolution and many mathematical data analysis were
employed to determine the principal frequencies noticeable in the measured
data. Both approaches try to predict the future evolution of the solar activity
and to understand the physical phenomena producing these cycles. Here we
present the analysis of the sunspots number evolution using the time-delay
approach. Our results show than the solar cycle can also be characterized by
this behavior implying the influence of the past evolution over the present
one, suggesting an histeresis mechanism, linked probably with magnetic
activity.
