This website uses astronomical reconstruction of the Judean night sky to fix some dates from the Gospel account. These are as follows:
1) Virgin Conception: September -2 CE, when Jupiter conjoined Regulus in Leo, and twice again in the next 9 months
2) Virgin Birth: June -1 CE, when Jupiter conjoined Venus (See this French site for details)
3) Adoration of the Magi: December 25, -1 CE, when Jupiter went into retrograde again
4) Crucifixion: April 3, 33 (they don't mention whether this is a Julian or Gregorian date, but for this part of the 1st century the 2 calendars coincide anyway). This is based on the confluence of three factors:
1) The moon went into eclipse at 3pm Jerusalem local time, and rose blood-red a few hours later in partial fulfillment of Joel's prophecy.
2) Passover fell on a Friday that year.
3) Pilate was on Tiberias Caesar's "naughty boy list" that year.
April 3, 33. A date Astronomically Fixed. But I guess we have to toss it out, because--confound it--it's the same date Ussher came up with in 1632.