Hi there

you haven't specified which sort of passport you are travelling on ( I would assume American but 9 years in the travel industry taught me never to assume anything about passports and visas ) and that is very important because all nationalities other than Australians and New Zealanders require a visa to enter Australia ( for many nations this is available as an ETA - commonly referred to as an "Electronic Visa ) however not everybody requires a visa to transit Australia .

Rules change constantly and it is best to check with either an Australian Embassy/Consulate or a trusted travel agent


edited to add : Where are my manners ? I forgot to say "Have a great trip ! "