Blue Sky, the United and JetBlue partnership just announced, will give frequent fliers more ways to earn and use miles. Here's what you need to know.

Two major U.S. airlines are joining forces in a blockbuster partnership. United Airlines will team up with JetBlue in a new alliance they are calling "Blue Sky," the carriers announced Thursday. The alliance will include a full-blown loyalty partnership that will allow United MileagePlus and JetBlue TrueBlue members the ability to earn and redeem miles on either carrier.

A new Blue Sky agreement, as the two airlines are calling it, will allow United to fly out of New York’s JFK Airport once again and will provide reciprocal earning and points redemption benefits, among other things.