To get the Xbox Live Achievement of "Star Gazer", you must form a star cluster. This is very easy. Look for a partially formed star cluster (two pieces) and just drop the last star piece in whenever one gets close enough to the cluster. Also, the pieces in a star cluster do not need to be the same color; they just need to be star pieces. Forming a star cluster also gives you a lot of points and usually gives you a large combo. Note: Do not destroy anything beneath a partially formed star cluster, or the star cluster will break apart.