The word kalachakra means cycles of time, and the Kalachakra system presents three such cycles – external, internal and alternative. The external and internal cycles deal with time as we normally know it, while the alternative cycles are practices for gaining liberation from these two.
The structures of the external and internal cycles are analogous, similar to the parallel between macrocosm and microcosm discussed in Western philosophy. This means that the same laws that govern a universe also pertain to atoms, the body and our experience of life.
The practices of the alternative cycles also follow this structure so as to allow us to engage with and surmount these forces in an efficient manner. Such mimicking is, in fact, one of the distinguishing features of the anuttarayoga tantra method.
Time, in Buddhism, is defined as a measurement of change. For example, a month is the measurement of change involved either externally in the moon circling the earth or internally in a woman going from one menstruation to the next. Such changes are cyclical in that the pattern repeats, although the events of each cycle are not completely identical. Externally, the universe passes through cosmic, astronomical, astrological and historical cycles (Click here for more information). – (Source:Kalachakra2017.net)