That may have been Comet Kohoutek in 1973 which was a bright 'Christmas Comet' visible to the naked eye between December 20, 1972 and January, 1973. It might also have been Comet Bennett in 1970. My bet is that it was Bennet because I saw both of these, and unless I knew where to look, I would never have seen Kohoutek which was then billed as potentially the brightest comet of all time.
Visit Gary Kronk's Comet Pages for more details.