The tl;dr: Extra 14C Beryllium in tree rings laid down at that time had to come from somewhere, and the best explanation at present is a gamma ray burst resulting from two neutron stars melding. This might have been visible; some say that a visible signature would have been in the sky for a while, but maybe not. The gamma ray burst itself would be one of those colorless odorless tasteless radioactive events that might cause some havoc on the cellular level but not in any way to be noticed as it happened. But later, maybe, there would be effects. For instance if any spiders were radiated and then they bit someone that person would have spider like qualities such as being able to shoot spider web out of his wrist. Or, somebody might start to turn very large and green whenever he was angry, but otherwise resemble Bill Bixby.
The thing is, you can never be sure what a major gamma ray burst from two neutron stars melding at a distance between 3K and 13K light years would do. It hardly every happens. So, in order to give due consideration to all possibilities, I’ve made a short list of things that happened around that time, and I invite you to add your ideas below in the comments section.
UPDATE: The “red crucifix” mentioned in the Anglo Saxon Chronicles was rules out because it happened the year after the burst would have been, but a closer examination of the Anglo Saxon Chronicles by Amy Gazin-Schwartz, a friend of mine and expert on the period and the literature, says it may have been possible. The event is listed under 775 but there is some ambiguity on the exact timing of the red crucifix. (You may be able to see that discussion here depending on permissions and access.)
Also, one Internet version of the Anglo Saxon Chronicles says “A.D. 744. This year Daniel resigned the see of Winchester; to which Hunferth was promoted. The stars went swiftly shooting; and Wilferth the younger, who had been thirty winters Bishop of York, died on the third day before the calends of May.” …. stars swiftly shooting? What the heck is that?
That is about the time Beowulf was written. Pippen the Short rose to power just a few years after the gamma ray burst. This is thee Mayan Classic Age, roughly.
This is about the beginning of the Medieval warm period, or the middle of it, or the start of the second part of it, or the beginning of an early version of the “little ice age” depending on where in the world you are and what particular paleoclimate squiggle you are looking at.
In North America, Native Americans were building an inordinate number of really cool effigy mounds at about this time.
I don’t know much about Japanese History, but the isotopic signature is very strong in that region of the world. I’m not sure what that means, but according to The Internet, here is what was going on in Japan:
749: A woman, Shomu’s daughter Koken, becomes empress (also known as “empress Shotoku”) and commissions one million (relief printed) copies of the Buddhist “dharani”
752: Japan’s emperor Shomu founds the temple Todaiji in Nara (largest wooden building in the world) with a colossal Buddha inside
I believe this was around the time other were building giant Buddhas as well. I wonder if any of them were green. Or angry. Or both!?!?!?!!
What do you think? Doesn’t look like much.