You will find that this is probably the easiest star in this course, as long as you know how to Wall Jump effectively. From the beginning, take the left path and head to the Black Hole area. Make your way to the slope with the boulders and go all the way to the top, but make sure you stop there. Going into look mode, take a glance upwards and you will see an alcove on either side of the door. When facing the door, the star will be in the alcove on the right, but it doesn’t matter which one you jump to first. You will need to perform a Wall Jump to get up there, though, which should be easy enough.