A list of historical comets observed at plural sites: the beginning of astronomy in Japan and Korea

Comets generally stay long in the sky and can be seen from many places on the surface of the Earth. We are interested in historical comets which were observed at plural sites. We have shown in a previous work (Tanikawa & Sôma, 2008) that in the seventh century, five comets were observed independently in China and Japan. From this fact and other data, we deduced that Japanese observational astronomy started in the seventh century. We know that, other than China and Japan, Korea and Vietnam had observational astronomy before the 9th century. We look for historical comets observed at plural sites by surveying the existing literature of respective countries. Examining the independence of the records, we provide a list of comets observed independently at plural sites. This strengthens the reliability of the records of comets. The list can be used for other purposes.