Historical refers to the past and is a word with the neutral meaning. Historic means ‘important, significant or famous, the one worth remembering’ and as such involves judgement. It is definitely true that a lot of ‘historic events’ or ‘historic moments’ happened in the past and they could also be referred to as ‘historical’. However, usually when we talk about them this is the other aspect (the one of the event’s significance) that is more important. Both adjectives do, however, have the same adverb form: historically.