Well 5 BC. This article/paper examines the astronomical/astrological data, observations and context surrounding the star of Bethlehem. The author, interestingly a Metallurgist/Material Scientist, does a pretty good job of identifying the star as a very bright comet that appeared in 5 BC. According to Chinese records, appearing between April and May of that year.
It's a long read, and kept my attention. Usually, I skim over, but the detail provided makes it worth while reading in detail.
http://www.asa3.org/ASA/topics/Astro...Humphreys.html