In 1770, it passed extremely close by the earth down to 0.0146 A.U. on
July 1, and reached to -2 mag. The light curve during three and a half
months between June and October yields the absolute magnitude of H10 =
The condition in 1776 was worst, not observable at all.
Kazuo Kinoshita's calculation revealed that it passed extremely close
by Jupiter down to 0.0016 A.U., then the perihelion distance increased
extremely from 0.7 A.U. up to 5.2 A.U.
It was observed with a heliocentric distance up to 1.2 A.U. in 1770.
So the brightness at the distance of 5.2 A.U. is completely
uncertain. It is about 18 mag in calculation, but it may be fainter
than 20 mag.
Kazuo Kinoshita's calculation reveals that it must have returned
around 1984, but it was not observed. It is natural to be missed at
that time because the comet must have been fainter than 18 mag.
It may be recovered in the next return around 2184.