 Transits of Venus are among the <unk> of predictable astronomical phenomena . They occur in a pattern that generally repeats every 243 years , with pairs of transits eight years apart separated by long gaps of 121 @.@ 5 years and 105 @.@ 5 years . The <unk> is a reflection of the fact that the orbital periods of Earth and Venus are close to 8 : 13 and 243 : 395 <unk> . 
