The Meteor Star is a defensive structure that prevents fleets from travelling in a particular direction. Although the path of the fleet will not change, it will have to encounter the Meteor Star before proceeding to its target. The Meteor Star is an excellent way to protect your Defensive Structures as your opposing fleets will have to destroy your Meteor Stars. It can allow 1-2 more rounds of firepower untouched from your Defensive Structures if placed properly. Meteor Stars are easy to destroy, but as the Meteor Star is leveled up, it becomes more of a BLOCK in the way for opposing fleets while your cannons and AA Guns do their magic.
Data as of 05/17/14
Note: Build times and construction costs may vary depending on your Energy Control and Rapid Defense Buildup research.