Good question - I had to check my Concise Oxford dictionary to get the distinction right. You are correct, they are both adjectives, but in most cases you are going to use historical. Historic is used when you refer to some particularly noteworthy event in the past. Such as, 'it was an historic moment when men first landed on the moon', or when the Berlin wall came down, or some such. Other than that, for referring to something or someone belonging to the past, you will want to use historical.

historic: considered important - a historic building historical: connected with the past - the historical background of the events connected with the study of history: historical documents