The Chinese comet observation in AD 773 January

The strong C-14 increase in the year AD 774/5 detected in one German and two Japanese trees was recently suggested to have been caused by an impact of a comet onto Earth and a deposition of large amounts of C-14 into the atmosphere (Liu et al. 2014). The authors supported their claim using a report of a historic Chinese observation of a comet ostensibly colliding with Earth's atmosphere in AD 773 January. We show here that the Chinese text presented by those authors is not an original historic text, but that it is comprised of several different sources. Moreover, the translation presented in Liu et al. is misleading and inaccurate. We give the exact Chinese wordings and our English translations. According to the original sources, the Chinese observed a comet in mid January 773, but they report neither a collision nor a large coma, just a long tail. Also, there is no report in any of the source texts about dust rain in the daytime as claimed by Liu et al. (2014), but simply a normal dust storm. Ho (1962) reports sightings of this comet in China on AD 773 Jan 15 and/or 17 and in Japan on AD 773 Jan 20 (Ho 1962). At the relevant historic time, the Chinese held that comets were produced within the Earth's atmosphere, so that it would have been impossible for them to report a collision of a comet with Earth's atmosphere. The translation and conclusions made by Liu et al. (2014) are not supported by the historical record. Therefore, postulating a sudden increase in C-14 in corals off the Chinese coast precisely in mid January 773 (Liu et al. 2014) is not justified given just the Th-230 dating for AD 783 +/- 14. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim