Map of the Stars is a quest item in Diablo III. It is only available during The Darkening of Tristram in January.
It can only be obtained by salvaging Wirt's Leg. Reading its description is a clue to access the Abandoned Farmstead. After solving the riddle, the map will vanish.
Secret Map
You probably weren't supposed to find this old map. It appears to have a hoof print stamped on it and the numbers 2, 1, 3.