Luke 23:44 states “And it was about the sixth hour (noon), and there was darkness over all the earth until the ninth hour (3 oclock).
If that was an eclipse, it is a mightly long eclipse, seeing as the longest an eclipse can last is only 7.5 minutes. But, if it was at Passover (which the text says it was) it could not have been an eclipse because Passover occurs in the middle of a lunar month, which means the moon would be full, at the opposite side of the earth from the sun.
Fortunately, two historians witnessed the event and noted it:
Thallus, a historian alive at the time, noted the event and described it in his now lost writings – his reference was preserved, however, by Julius Africanus, who wrote in AD 221 the following:
“Thallus, in his third book of histories, explains away this darkness as an eclipse of the sun – unreasonably as it seems to me. For the Hebrews celebrate the Passover on the 14th day according to the moon, and the passion of our Saviour falls on the day before the passover; but an eclipse of the sun takes place only when the moon comes under the sun. And it cannot happen at any other time but in the interval between the first day of the new moon and the last of the old, that is, at their junction: how then should an eclipse occur when the moon is almost diametrically opposite the sun?”
Phlegon of Tralles, a first century Greek historian wrote Olympiades not long after the death of Jesus, in which he writes:
“In the 4th year of the 202nd Olympiad,there was a great eclipse of the Sun, greater than had ever been known before, for at the 6th hour the day was changed into night and the stars were seen in the heavens. An earthquake occurred in Bythinia and overthrew a great part of the city of Nicæa.”
The 202nd Olympiad, according to calculations, ran from July AD 29 to June AD 33. If the event occurred during the fourth year of the Olympiad, that would mean Passover, or Spring, AD 33.
Christian Think Tank discussion of Thallus and Julius Africanus