The solar cycle is 22 years long because the magnetic polarity of the sun flips at the beginning of a new activity cycle, but it takes months to years for the polarity to flip completely. Some sunspot groups even in June and July of this year still had the magnetic polarity of solar activity cycle 23, It's only been the two months, or less, that the magnetic polarity of sunspot groups have solar activity cycle 24's magnetic polarity. Arbitrary, if the first sunspot of group in activity cycle 23 was positive. the magnetic polarity of the first sunspot of sunspot group in activity cycle will be negative. After the second half of solar activity cycle 24 starts, the magnetic polarity of the first sunspot of a sunspot group will again be positive. It takes 22 years for complete magnetic polarity cycle, but solar activity will have two minimum within that 22 year cycle and one maximum.