What happened in 774 AD?

Answer 1

The one thing everyone can agree on is that something strange happened in the year 774, and that whatever it was sent a burst of high-energy particles into the Earth's atmosphere. Exactly what that event was, however, has remained the subject of contention. And, it's back in the news today, with a new study pointing the finger at a rare event called a short gamma-ray burst.

The reason for the part that people agree on is an unusually large spike in the amount of radioactive carbon found in tree rings that have been dated back to 774. That apparently is correlated with the timing of a surge in a specific isotope of beryllium, detected in ice cores of Antarctica. Both of these isotopes are the product of collisions that take place in our atmosphere, produced by energetic particles striking some of the gasses normally resident there.

Answer 2

In 774 AD, Charlemagne, King of the Franks, conquered the Lombard Kingdom in Italy, expanding his empire. Additionally, there were reports of a red aurora seen across the night sky in Europe, which is believed to have been a massive solar storm event.