  The anomalous concentration of radiocarbon in 774/775 attracted intense
discussion on its origin, including the possible extreme solar event(s)
exceeding any events in observational history. Anticipating such extreme solar
events, auroral records were also surveyed in historical documents and those
including the red celestial sign after sunset in the Anglo-Saxon Chronicle
(ASC) were subjected to consideration. Usoskin et al. (2013: U13) interpreted
this record as an aurora and suggested enhanced solar activity around 774/775.
Conversely, Neuhauser and Neuhauser (2015a, 2015b: N15a and N15b) interpreted
"after sunset" as during sunset or twilight; they considered this sign as a
halo display and suggested a solar minimum around 774. However, so far these
records have not been discussed in comparison with eyewitness auroral records
during the known extreme space-weather events, although they were discussed in
relationship with potential extreme events in 774/775. Therefore, we
reconstruct the observational details based on the original records in the ASC
and philological references, compare them with eyewitness auroral observations
during known extreme space-weather events, and consider contemporary solar
activity. We clarify the observation was indeed "after sunset", reject the
solar halo hypothesis, define the observational time span between 25 Mar. 775
and 25 Dec. 777, and note the parallel halo drawing in 806 in the ASC shown in
N15b was not based on the original observation in England. We show examples of
eyewitness auroral observations during twilight in known space-weather events,
and this celestial sign does not contradict the observational evidence.
Accordingly, we consider this event happened after the onset of the event in
774/775, but shows relatively enhanced solar activity, with other historical
auroral records in the mid-770s, as also confirmed by the Be data from ice
cores.
