Comets are non-sentient and have no will for good or evil. There is probably no such thing as "luck".
The real question is how God balances His foreknowledge and creative hand against the free will of each human being in such a manner that disasters work to God's will and to the good of his children even as they bring temporary grief to his own and damnation to those who have rebelled. God, in His wisdom and power, is indeed awesome in the truest sense of the word.