I am wanting to know if the triple conjunction of Jupiter with Regulus in: Sep 10, 3 BC Feb 7, 3 BC & May 8, 2 BC with Jupiter later having a conjunction with Venus in Jun 17, 2 BC has happened since, and if so, how often does this triple conjunction happens?
With any given star, Jupiter has 3 or 4 triple conjunctions per century, with either 12 or 71 years in between. These occur with Regulus in 1873, 1885, 1956, 1968, 2039, 2051, 2063, 2134, and 2146.
Jupiter takes 11.9 years to orbit the Sun, advancing at a fairly steady ~30° per year. From Earth, Jupiter appears to move ~40° forward and ~10° backward in a 13-month cycle. The retrograde loop happens when Earth and Jupiter are on the same side of the Sun.
We see a triple conjunction with a star when the retrograde loop encompasses it. Around the February 2051 opposition, Jupiter has conjunctions with Regulus in October, February, and June:
If Jupiter passes a star while Earth is on the other side of the Sun, we see only a single conjunction, as in August 2003:
Jupiter-Venus conjunctions occur at intervals of 10 or 14.5 months. The Jupiter-Venus conjunctions of October 1884 and July 2146 occur reasonably close to a Jupiter-Regulus conjunction in a triplet listed above and far enough from the Sun to observe easily.