Where do you go to catch Cresselia in Pokemon platinum?

You go to canlave after obtaining the national pokedex and go into the sailers house and talk to the women. then go outside and talk to the sailer and he will sey some stuff and then ask you to get the lunar wing at fullmoon island. if you say yes you will go get cresselia. she will run away so you will need a marking map app for your poketch.