The Star Festival is an event that occurs in the Mushroom Kingdom every hundred years and appears in Super Mario Galaxy as a game chapter. It is celebrated by the special comet that travels through the Mushroom Kingdom also every hundred years.
Super Mario Galaxy
In Super Mario Galaxy, the Toads gathered in the Castle Gardens to celebrate and get ready for the Star Festival. In this game strangely, there were comets in the shape of Star Bits that fell to the ground. The Toads were outside and were enjoying collecting the Star Bits and there was even a Star Bit shaped like a Grand Star that the Toads gave to Princess Peach and Peach even found a Luma that fell from the sky. Later, Peach invited Mario to the party and gave him a Luma as a gift. Later, Bowser crashed the party and stole Princess Peach's Castle along with Peach herself and shot cannons out of the airship and attacked the Mushroom Kingdom.