 The pattern of 105 @.@ 5 , 8 , 121 @.@ 5 and 8 years is not the only pattern that is possible within the 243 @-@ year cycle , because of the slight <unk> between the times when the Earth and Venus arrive at the point of conjunction . Prior to 1518 , the pattern of transits was 8 , 113 @.@ 5 and 121 @.@ 5 years , and the eight inter @-@ transit gaps before the AD <unk> transit were 121 @.@ 5 years apart . The current pattern will continue until <unk> , when it will be replaced by a pattern of 105 @.@ 5 , 129 @.@ 5 and 8 years . Thus , the 243 @-@ year cycle is relatively stable , but the number of transits and their timing within the cycle will vary over time . Since the 243 : 395 Earth : Venus <unk> is only approximate , there are different sequences of transits occurring 243 years apart , each extending for several thousand years , which are eventually replaced by other sequences . For instance , there is a series which ended in <unk> BC , and the series which includes 2117 only started in AD 1631 . 
