This darkness was not recorded by the two greatest contemporary scientists of the time, Seneca and Pliny the Elder. These writers attempted to record all known contemporary geological and astronomical phenomenon, which makes their omission of this event a serious deterrent to regarding it as historical. It is also not mentioned by Josephus, who certainly should have noted it.
This objection is sometimes tendered, and I really wonder if those who make it have actually read the works of Seneca and Pliny in question - rather than simply, say, repeating Edward Gibbon's remarks on the subject!
Pliny's work is entitled Natural History [Plin.NH], and it is a multi-volume work covering a wide variety of subjects - geography, meteorology, mineralogy, zoology, and botany. Volume 2 of this work is concerned with cosmology and astronomy, and is the place we might expect Pliny to have recorded this event - if he indeed did intend to record all such events. However, there is absolutely no indication that this was Pliny's intent - he offers examples, he makes descriptions, but nowhere is there any indication that his work is intended to be an exhaustive catalog of all possible relevant data.
More to the point, it is doubtful that Pliny would have recorded this event in any case, unless he had been there himself. The darkness at the crucifixion, as we see from Thallus, defied natural explanation, and had the character of a miracle; and this is precisely the sort of event that Pliny would pass over in disdain - for he was a skeptic and a rationalist of the highest order. Consider these words from Pliny's pen [ibid., 179, 183]:
I deem it a mark of human weakness to seek to discover the shape and form of God.
That that supreme being, whatever it be, pays heed to man's affairs is a ridiculous notion.
Given the above, what would this writer have made of reports of a miraculous and unexplained darkness? My guess is, he would turn up his nose and relegate the matter to the wastebasket. He would consider such reports unworthy of his attention and not worth recording.
What, then, of Seneca and his work, Naturales Questiones [Sen.NQ]? There is even less cause to suppose mention of the darkness here. Seneca's work is mostly theoretical surveys of natural phenomena - by no means an attempt at an exhaustive catalog of events - and Seneca is far more concerned with drawing morals from what he records that with listing events, of which he does very little.
As for Josephus, while that may seem a tougher one, it isn't -- we need to keep in mind a major constraint Josephus was under at the time. Josephus was writing for the favor of his patron Vespasian, whom he had credited with fulfillment of Messianic prophecy. Josephus was quite safe mentioning that Jesus did miracles, but to ascribe to Jesus some sign that would have signified special status with God -- like the darkness -- would have been at cross-purposes with what his patron would have been happy with.
Bottom line: For this objection to have any force, it must be shown why these writers should have included a reference to the darkness - but for Seneca and Pliny, there is simply no evidence that they should have, or would have been interested in recording it, and Josephus would have been inclined if anything to not report it.
Pliny -- Not Too Bright?
In response to my point about Pliny being a rationalist and skeptic, someone produced this this quote from Pliny's Natural History:
'It is also reported that once several suns were seen at midday at the Bosphorus, and that these lasted from dawn till sunset. In former times three suns have often been seen at once, for example in the consulships of Spurius Postumius and Quintus Mucius of Quintus Marcius and Marcus Porcius, of Marcus Antonius and Publius Dolabellal and of Marcus Lepidus and Lucius Plancus; and our generation saw this during the principate of his late Majesty Claudius, in his consulship, when Cornelius Orfitus was his colleague. It is not stated that more than three suns at a time have ever been seen hitherto.'
and Pliny continues 'Also three moons have appeared at once, for instance in the consulship of Gnaeus Domitius and Gaius Fannius.'
The apparent point here being, that our critic thought that this was a "miracle" that Pliny felt was worth reporting. But that's just the problem. Apparently, Pliny did not think of this as a miracle, but as a natural event -- and that is precisely what it is.
Here is an example of that very phenomenon -- it's called a "sun dog." (It happens with the moon sometimes, too.) It's a phenomenon that many witnesses describe as looking like three suns, just as Pliny did. For example, see here:
May I use this opportunity to correct another popular misconception about Die Winterreise. In the penultimate song, its protagonist sees "three suns" in the sky. This is frequently taken as an indication that he is not in his right mind, but in fact, the phenomenon of "mock suns" or "sun dogs"-pillars of light on either side of the sun-really exists. It is discussed by Kenneth Heuer in his book, Rainbows, Halos and Other Wonders. It may also be worth mentioning that Schubert died of typhus fever, not of tuberculosis.
And here's another from a link now dead, formerly at http://www.simhq.com/simhq3/hardware/interviews/matrox/parhelia/:
Good question, figured a few people would be scratching their heads at that one. A Parhelia is an atmospheric effect which occurs when sunlight is diffracted by ice crystals in the lower atmosphere. The result is the illusion of two smaller suns on either side, or Sun dogs as they are also referred to. We have a flash demo that shows the animated effect. As the Parhelia-512 delivers top-notch quality, performance and features (three suns), supports three displays and is the world's first 512-bit GPU, what could be more appropriate than the Parhelia-512?
Another, from the now defunct http://www.hum.gu.se/arkiv/ONN/1998onn/II/msg00160.html:
One more, from the now-defunct http://www.frozentoes.com/expedition/reports/report5.htm:
It was late in the afternoon. We set off again. The sun was low in the arctic north west, straddled by a pair of beautiful sun dogs, an atmospheric phenomena where the sunlight is refracted by upper atmospheric ice crystals and on either side of the sun an apparition of the sun appears. It can look as if there are three suns hanging low in the sky.
Flummoxed by these quotes, my critic tried a new tack:
Pliny writes 'Historical record also exists of thunderbolts being either caused by or vouchsafed in answer to certain rites and prayers. There is an old story of the latter in Tuscany, when the portent which they called Olta came to the city of Bolsena, when its territory had been devastated; it was sent in answer to the prayer of its king Porsina.'
But we need to quote some more relevant words from that passage in Pliny....
On this matter the opinion of mankind varies, in correspondence with our individual dispositions. It takes a bold man to believe that Nature obeys the behests of ritual, and equally it takes a dull man to deny that ritual has beneficent powers, when knowledge has made such progress even in the interpretation of thunderbolts that it can prophecy that others will come on a fixed day, and whether they will destroy a previous one or other previous ones that are concealed: this progress has been made by public and private experiments in both fields. In consequence although such indications are certain in some cases but doubtful in others, and approved to some persons but in the view of others to be condemned, in accordance with Nature's will and pleasure, we for our part are not going to leave out the rest of the things worth recording in this department.
It seems that Pliny doesn't attribute this to deities or divine intervention, does he? "Nature obeys" -- not Jove, even if he was the subject of the prayer? Ritual has beneficient powers -- not "the gods can do this"? Pliny may have been gullible at times, and his scientific interpretations are ofren quite fanciful from our later perspective -- but he was sure no proponent of the concept of divine intervention.
So in sum:
Pliny often recorded things which defied rational explanation, but he never recorded things atrributed to divine intervention, as such; he recorded things that we know, in "hindsight", defied rational explanation -- even as he himself, not having enough data, may not have thought they did. In other words, we know that a rain of bricks, and that dog-headed people, "defy rational explanation"; but Pliny would hardly have been in a position to say so himself, lacking as he did the data that tells us what is irrational! To be a Skeptic or rationalist in Pliny's time was a much broader equation.
None of Pliny's reports of things like heavenly armies; rains of milk, blood, iron, wool or bricks; of unspoiled carrion; of fire in the sky -- are examples from Pliny of "a supreme being" paying heed to man's affairs, as the darkness was credited to be.