Wii Mario Galaxy

[{Dakota}]

I've collected 90 of the 120 stars in Mario Galaxy but there's something I'm not understanding;

I unlocked the red star in "The Gate" that lets me fly to get the purple coins, but I haven't come across any purple star comets yet. The only time I have seen the red star outside "The Gate" is in the Luma's home beside "The Workshop", no purple stars appear when I hop into it and the flying ability doesn't follow me into any of the galaxies.

Am I missing something?