"And it came about during this year that a most dread portent took place. For the sun gave forth its light without brightness, like the moon, during this whole year, and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear nor such as it is accustomed to shed" - Procopius (Wars, 4.14.5)
The surprising result of the new work is just how small a comet is needed to cause such dramatic effects. The scientists calculate that a comet not much more than half a kilometre across could cause a global nuclear winter effect. This is significantly smaller than was previously thought.
Dr. Ward-Thompson said: "One of the exciting aspects of this work is that we have re-classified the size of comet that represents a global threat. This work shows that even a comet of only half a kilometre in size could have global consequences. Previously nothing less than a kilometre across was counted as a global threat. If such an event happened again today, then once again a large fraction of the earth's population could face starvation."
The comet impact caused crop failures and wide-spread starvation among the sixth century population. The timing coincides with the Justinian Plague, widely believed to be the first appearance of the Black Death in Europe. It is possible that the plague was so rampant and took hold so quickly because the population was already weakened by starvation.
1, 2 seconds top to bottom. Quick drop, rainbow trail, bright flash. Exceptionally bright black trail in the sky after 3 minutes. White colour, impressive.18 January 2014 - Tim North, Shields, UK 20:18 approx
2 seconds duration. Facing east, track Northwest to Southeast over sea, to right of Moon. Barium green, small amount white. Slightly brighter than the moon. No fragmentation, just one discontinuity. Have CCTV video available.18 January 2014 - James Cambuslang, Lanarkshire, UK 20:00 UTC approx
2 seconds duration. Seen to the east of my location, falling to Earth in southerly direction. Green trail, twice as bright as Sirius.
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30 Dec 2013: Mysterious loud boom rattles, rolls most of Texas City