I beg to differ. Sirius positively must be an Aries. He's bull-headed (or - sheep-headed?), short-tempered, determined, and a firey hotpotch of impetuosity. He's brash enough to make as many enemies as friends, and would rather be the trail-blazer than the follower. (Or the guy who stands on the sidelines and makes sarcastic remarks while everyone else is doing all the work.) Not to mention the fact that he's vindictive and just a little heartless. Of course, being loaded up with responsibility brings out his caring, protective, loyal side. I almost feel sorry for the Dursleys, dealing with a godfather like Sirius.
I don't think he has a cold, calculating side. I should think he "plays it by ear" most of the time. Remember, knowing that Pettigrew was alive all but sent him over the deep end. He barely planned his movements at all. He almost got himself killed by his own godson, for crying out loud! Why didn't he just explain what he wanted, instead of playing word games? (Yeah yeah, dramatic necessity strikes again.)
Remus is an Aquarius all over. Definitely.
Mmm. I should go look up the Celtic signs. But for now ... I'M GONNA GO OUTSIDE AND ENJOY THE SNOW! YEEHAW!