Nature recently posted an article about a MASSIVE radiation burst that occurred around 774-775 CE but was never observed. How could this be? Who knows?, No one. There were astronomers scanning the heavens at that time. Among them some of the most advanced were in China, yet no notice was taken of this massive radiation burst.
I got to thinking that also at the time of this event (I am hesitant to say solar, since no one really knows its origin.) the Mayan mysteriously vanished. Well, vanished might be overstating the case since the Mayan are still with us. What vanished was a very sophisticated civilization. This is called the Classic Mayan Collapse and it began around 795 CE and lasted into the 9th Century. Many theories account for the Classic Mayan Collapse, but the one given the most creduality is the drought theory. Who knows? No one. Oh, and if you want more unique theories about the New World in general and MesoAmerica in particular read Charles Mann's book, 1491.
The massive radiation burst may have occurred in southern skies and I speculate that it may have impacted the Classic Mayan Collapse, casting my lot with the drought theory crowd.
Summing up the only thing scientist know for certain is that a massive radiation burst event happened between 774 and 775 CE. It was never observed at the time. We have found a galaxy whose light took 800 million years to get to earth, but we can't find the remnants of the massive radiation burst from the 8th Century. We know of the Classic Mayan Collapse but not why?
Nature: "Mysterious radiation burst recorded in tree rings", by Richard A. Lovett, 06-03-2012
Climate History: Drought and the Collapse of the Maya Civilsation
National Geographic: "The Maya: Glory and Ruin", by Guy Gugliotta, 08-2007
NOAA: "The Sun and Sunspots: Can an increase or decrease in sunspot activity affect the earth's climate?", 10-07-2012
asu news [science & tech]: "ASU astronomers discover faintest distant galaxy", by Nikki Cassis, 06-01-2012