  Solar activity has been recorded as auroras or sunspots in various historical
sources. These records are of much importance for investigating both long-term
solar activities and extremely intense solar flares. In previous studies, they
were recorded as "vapor," "cloud," or "light," especially in oriental
historical sources; however, the terminology was not discussed adequately and
is still quite vague. In this paper, we suggest the possibility of "unusual
rainbow" and "white rainbow" as candidates of historical auroras in oriental
historical sources and examine if it is probable. This discovery will help us
to make more comprehensive historical auroral catalogues and require us to add
these terms to auroral candidates in oriental historical sources.
