Maybe twice in a lifetime. The last one was in 2004. From Wikipedia, "Transits of Venus are among the rarest of predictable astronomical phenomena. They occur

Maybe twice in a lifetime. The last one was in 2004. From Wikipedia, "Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years."